Life Lexicon

Release 30oas, 2019 January 21
Single-page HTML Viewer Version

INTRODUCTION

This is a lexicon of terms relating to John Horton Conway's Game of Life. An ASCII version and a multipage HTML version are also available.

This lexicon was originally compiled between 1997 and 2006 by Stephen A. Silver, and was updated in 2016-17 by Dave Greene; subsequently addended by Otis Arron Schmakel. See below for additional credits.

The latest versions of this lexicon (both HTML and ASCII) should be available from the Life Lexicon Home Page.

CREDITS

The largest single source for the early versions of this lexicon was a glossary compiled by Alan Hensel "with indispensable help from John Conway, Dean Hickerson, David Bell, Bill Gosper, Bob Wainwright, Noam Elkies, Nathan Thompson, Harold McIntosh, and Dan Hoey".

Other sources include the works listed in the bibliography at the end of this lexicon, as well as pattern collections by Alan Hensel and David Bell (and especially Dean Hickerson's file stamp.l in the latter collection), and the web sites of Mark Niemiec, Paul Callahan, Achim Flammenkamp, Robert Wainwright and Heinrich Koenig. Recent releases also use a lot of information from Dean Hickerson's header to his 1995 stamp file.

Most of the information on recent results is from the discoverers themselves.

The following people all provided useful comments on earlier releases of this lexicon: David Bell, Nicolay Beluchenko, Johan Bontes, Daniel Collazo, Scot Ellison, Nick Gotts, Ivan Fomichev, Dave Greene, Alan Hensel, Dean Hickerson, Dieter Leithner, Mark Niemiec, Gabriel Nivasch, Andrzej Okrasinski, Arie Paap, Peter Rott, Chris Rowett, Tony Smith, Ken Takusagawa, the user with the handle 'thunk' on the conwaylife.com forums, Andrew Trevorrow, and Malcolm Tyrrell.

The format, errors, use of British English and anything else you might want to complain about are by Stephen Silver -- except that for post-Version 25 definitions, everything besides the British English may well be Dave Greene's fault instead.

COPYING

This lexicon is copyright (C) Stephen Silver, 1997-2017. It may be freely copied, modified and distributed under the terms of the Creative Commons Attribution-ShareAlike 3.0 Unported licence (CC BY-SA 3.0), as long as due credit is given. This includes not just credit to those who have contributed in some way to the present version (see above), but also credit to those who have made any modifications.

LEXICOGRAPHIC ORDER

I have adopted the following convention: all characters (including spaces) other than letters and digits are ignored for the purposes of ordering the entries in this lexicon. (Many terms are used by some people as a single word, with or without a hyphen, and by others as two words. My convention means that I do not have to list these in two separate places. Indeed, I list them only once, choosing whichever form seems most common or sensible.) Digits lexicographically precede letters.

FORMAT

The main thing to note about the format of the HTML version is that all keywords are preceded by a colon. For example, entering :foo in the dialogue box of your browser's Find command will take you straight to the definition of the first word beginning with "foo" (or at least it would if there were any). This is the recommended way of finding a particular definition when there is no link to click on.

The diagrams in this lexicon are in a very standard format. You should be able to simply copy a pattern, paste it into a new file and run it in your favourite Life program. If you use Golly then you can just paste the pattern directly into the Life program. Diagrams are generally restricted to size 64×64 or less.

Most definitions that have a diagram have also some data in brackets after the keyword. Oscillators are maked as pn (where n is a positive integer), meaning that the period is n (p1 indicates a still life). Wicks are marked in the same way but with the word "wick" added. For spaceships the speed (as a fraction of c, the speed of light), the direction and the period are given. Fuses are marked with speed and period and have the word "fuse" added. Wicks and fuses are infinite in extent and so have necessarily been truncated, with the ends stabilized wherever practical.

SCOPE

This lexicon covers only Conway's Life, and provides no information about other cellular automata. David Bell has written articles on two other interesting cellular automata: HighLife (which is similar to Life, but has a tiny replicator) and Day & Night (which is very different, but exhibits many of the same phenomena). These articles can be found on his website.

ERRORS AND OMISSIONS

If you find any errors (including typos) or serious omissions, then please email b3s23life@gmail.com with the details. As of August 2017 this email address is monitored by Dave Greene.

NAMES

When deciding whether to use full or abbreviated forms of forenames I have tried, wherever possible, to follow the usage of the person concerned.

QUOTE

Every other author may aspire to praise; the lexicographer can only hope to escape reproach.    Samuel Johnson, 1775

DEDICATION

This lexicon is dedicated to the memory of Dieter Leithner, who died on 26 February 1999.

RE-DEDICATION

This lexicon version is all about Viro, also known as glider.

:0GtoP (a.k.a. IMP) Found by Otis Arron Schmakel in December 2004. Viro (a.k.a. glider) interacts with three blocks and a traffic light to produce a great S, a block, a blinker, and a Cambridge Pulsar ( initials O. S. ).

.......................O..
.......................O.O
.......................OO.
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O.....O...................
O.....O...................
O.....O...................
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:0hd Demonoid See Demonoid.

:101 (p5) Found by Achim Flammenkamp in August 1994. The name was suggested by Bill Gosper, noting that the phase shown below displays the period in binary.

	....OO......OO....
	...O.O......O.O...
	...O..........O...
	OO.O..........O.OO
	OO.O.O..OO..O.O.OO
	...O.O.O..O.O.O...
	...O.O.O..O.O.O...
	OO.O.O..OO..O.O.OO
	OO.O..........O.OO
	...O..........O...
	...O.O......O.O...
	....OO......OO....

:10hd Demonoid See Demonoid.

:11IGN Ignition Phase of a constructed Period Eleven Oscillator.

.......................................................O.....................
.........O.............................................O.O...................
..........O............................................OO....................
........OOO..................................................................
..........................................O..................................
.........................................O...................................
.........................................OOO..............O..................
...............O.........................................O...................
................O........................................OOO............O....
..............OOO.......................................................O.O..
........................................................................OO...
.......................................O.O.....O.............................
..............O.............O..........OO....OO..............................
...............O.............O..........O.....OO.............O...............
.............OOO...........OOO...............................O.O..O..........
.............................................................OO...O.O........
........O.........................................................OO.........
......O.O....................................................................
.O.....OO....................................................................
..O..........................................................................
OOO.......................................O..................................
...........................................OO................................
..........................................OO.................................
.............................................................................
...............................................O.O...........................
................................................OO...........................
........................OO......................O............................
.........................OO..................................O...............
...........O.O..........O....................................O.O.............
............OO..................O...OO.....O.................OO..............
............O..................O.O..OO....O.O................................
.....................O........O.O..........O.O...............................
......O..............OO......O.O....OOOO....O.O..............................
....O.O.............O.O.......O.....O..O.....O...............................
.....OO....O.................................................................
............OO...............................................................
...........OO...................OO........OO.OO..............................
................................O..........O.OO..............................
.............................OO.O..........O.................................
.............................OO.OO........OO...................OO............
..............................................................OO.............
................................................................O....OO......
..............................O.....O..O.....O.......O.O.............O.O.....
.............................O.O....OOOO....O.O......OO..............O.......
..............................O.O..........O.O........O......................
...............................O.O....OO..O.O..................O.............
.............OO.................O.....OO...O..................OO.............
............O.O....................................O..........O.O............
..............O..................................OO..........................
...........................O......................OO.........................
..........................OO.................................................
..........................O.O................................................
.............................................................................
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...............................OO............................................
.................................O.......................................OOO.
.........................................................................O...
...................................................................OO.....O..
...................................................................O.O.......
........OO.........................................................O.........
.......O.O...OO..............................................................
.........O..O.O...............................OOO...........OOO..............
..............O.............OO.....O..........O.............O................
.............................OO....OO..........O.............O...............
............................O.....O.O........................................
..OO.........................................................................
.O.O.......................................................OOO...............
...O............OOO........................................O.................
..................O.........................................O................
.................O..............OOO..........................................
..................................O..........................................
.................................O...........................................
.................................................................OOO.........
...................OO............................................O...........
..................O.O.............................................O..........
....................O........................................................

:119P4H1V0 (c/4 orthogonally, p4) A spaceship discovered by Dean Hickerson in December 1989, the first spaceship of its kind to be found. Hickerson then found a small tagalong for this spaceship which could be attached to one side or both. These three variants of 119P4H1V0 were the only known c/4 orthogonal spaceships until July 1992 when Hartmut Holzwart discovered a larger spaceship, 163P4H1V0.

	.................................O.
	................O...............O.O
	......O.O......O.....OO........O...
	......O....O....O.OOOOOO....OO.....
	......O.OOOOOOOO..........O..O.OOO.
	.........O.....O.......OOOO....OOO.
	....OO.................OOO.O.......
	.O..OO.......OO........OO..........
	.O..O..............................
	O..................................
	.O..O..............................
	.O..OO.......OO........OO..........
	....OO.................OOO.O.......
	.........O.....O.......OOOO....OOO.
	......O.OOOOOOOO..........O..O.OOO.
	......O....O....O.OOOOOO....OO.....
	......O.O......O.....OO........O...
	................O...............O.O
	.................................O.

:1-2-3 (p3) Found by Dave Buckingham, August 1972. This is one of only three essentially different p3 oscillators with only three cells in the rotor. The others are stillater and cuphook.

	..OO......
	O..O......
	OO.O.OO...
	.O.O..O...
	.O....O.OO
	..OOO.O.OO
	.....O....
	....O.....
	....OO....

:1-2-3-4 (p4) See also Achim's p4.

	.....O.....
	....O.O....
	...O.O.O...
	...O...O...
	OO.O.O.O.OO
	O.O.....O.O
	...OOOOO...
	...........
	.....O.....
	....O.O....
	.....O.....

:12G Twelve Glider Explosion. Three Virii come together to breed Thirteen; one early escapee is eaten by the Eater; Twelve Virii Explode from the remaining pattern. Four proceed to OAS GtoP, another one succumbs to the Eater, and the rest escape.

...............OO.........................................................................................OO...............
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..OO...................................................................................................................OO..
..OO...................................................................................................................OO..
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..OOO.....OO...................................................................................................OO.....OOO..
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O.....O.............................................................................................................O.....O
O.....O.....................................................................................O.O.....................O.....O
O.....O.....................................................................................OO......................O.....O
.............................................................................................O.............................
..OOO.................................................................................................................OOO..
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..OOO.................................................................................................................OOO..
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O.....O.............................................................................................................O.....O
O.....O.............................................................................................................O.....O
O.....O........................................................................................OOO..................O.....O
...............................................................................................O...........................
..OOO.....OO..................OO................................................................O..............OO.....OOO..
..........OO.................O.O...............................................................................OO..........
...............................O...........................................................................................
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..OO...........................................................................................OO.OO...................OO..
..OO............................................................................................O.OO...................OO..
................................................................................................O..........................
..............................................................................................O.O..........................
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...............OO.........................................................................................OO...............

:135-degree MWSS-to-G The following converter, discovered by Matthias Merzenich in July 2013. It accepts an MWSS as input, and produces an output glider traveling at a 135-degree angle relative to the input direction.

	......OO......
	......O.O.OO.O
	........O.O.OO
	........OO....
	..............
	..............
	.OOOOO.....OO.
	O....O.....OO.
	.....O........
	O...O.........
	..O...........

:14-ner = fourteener

:17c/45 spaceship A spaceship travelling at seventeen forty-fifths of the speed of light. This was the first known macro-spaceship speed. See Caterpillar for details.

:180-degree kickback The only other two-glider collision besides the standard kickback that produces a clean 180-degree output glider. It is occasionally useful in glider synthesis, but is rarely used in signal circuitry or in self-supporting patterns like the Caterpillar or Centipede, because 90-degree collisions are generally much easier to arrange.

	.O.
	O..
	OOO
	...
	...
	.OO
	O.O
	..O

:1G seed See seed.

:(23,5)c/79 The rate of travel of the Herschel climber reaction used in the self-supporting waterbear knightship.

:(23,5)c/79 Herschel climber The following glider-supported reaction used in the waterbear, which can be repeated every 79 ticks, moving the Herschel 23 cells to the right and 5 cells upward, and releasing two gliders to the northwest and southwest. As the diagram shows, it is possible to substitute a loaf or other still lifes for some or all of the support gliders. This fact is used to advantage at the front end of the waterbear.

	...............O.O...............O..
	...............OO...............O.O.
	................O...............O..O
	.................................OO.
	....................................
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	....................................
	....................................
	....................................
	....................................
	....................................
	O...................................
	O.O.................................
	OOO.................................
	..O.................................

:24-cell quadratic growth A 39786×143 quadratic growth pattern found by Michael Simkin in October 2014, two days after 25-cell quadratic growth and a week before switch-engine ping-pong.

:25-cell quadratic growth A 25-cell quadratic growth pattern found by Michael Simkin on October 2014, with a bounding box of 21372×172. It was the smallest-population quadratic growth pattern for two days, until the discovery of 24-cell quadratic growth. It superseded 26-cell quadratic growth, which had held the record for eight years.

:25P3H1V0.1 (c/3 orthogonally, p3) A spaceship discovered by David Bell, with a minimum of 25 cells -- the lowest number of cells known for any c/3 spaceship. See also edge-repair spaceship for a very similar c/3 spaceship with a minimumm population of 26.

	..........O.....
	........OOO.OOO.
	.......OO......O
	..O...O..O...OO.
	.OOOO...........
	O...O...........
	.O.O..O.........
	.....O..........

:25P3H1V0.2 (c/3 orthogonally, p3) A spaceship discovered by Dean Hickerson in August 1989. It was the first c/3 spaceship to be discovered. In terms of its 25 cells, it is tied with 25P3H1V0.1 as the smallest c/3 spaceship. Unlike 25P3H1V0.1, it has a population of 25 in all of its phases, as well as a smaller bounding box.

	.......OO.O.....
	....OO.O.OO.OOO.
	.OOOO..OO......O
	O....O...O...OO.
	.OO.............
Martin Grant discovered a glider synthesis for 25P3H1V0.2 on 6 January 2015.

:26-cell quadratic growth A quadratic growth pattern found by Nick Gotts in March 2006, using ideas found in metacatacryst and Gotts dots. It held the record for the smallest-population quadratic growth pattern for eight years, until it was surpassed by 25-cell quadratic growth.

:295P5H1V1 (c/5 diagonally, p5) The first spaceship of its type to be discovered, found by Jason Summers on 22 November 2000.

	.............OO.....................................
	.....OO....OO.O.O...................................
	....OOO....OOOO.....................................
	...OO......OO.....O.................................
	..OO..OO...O..O..O..................................
	.OO.....O.......O..OO...............................
	.OO.O...OOOO........................................
	....O...OO..OO.O....................................
	.....OOO....O.O.....................................
	......OO...OO..O....................................
	......O.....O.......................................
	.OOOO.O..O..O...O...................................
	.OOO...OOOOO..OOOOOOO.O.............................
	O.O....O..........O..OO.............................
	OOO.O...O...O.....OOO...............................
	.......O.O..O.......OO..............................
	.O...O.....OO........OO..O.O........................
	....O.......O........OOO.O.OOO......................
	...O........OOO......O....O.........................
	.....O......O.O.....O.O.............................
	.....O......O.OO...O....O...........................
	.............O.OOOO...O.....O..O....................
	............OO..OO.O.O...O.OOO......................
	.................O......O..OOO...OOO................
	....................O..O......OO....................
	................OO....O..O..........OO..............
	..................O.............O...O...............
	................OO....OO........O...................
	.................O...OOO........O.O.O.O.............
	.................O....OO........O.....OO............
	........................O........O..OOO.............
	.....................O..O........O........O.........
	..........................OOOO........OO...O........
	.......................O......OO......OO...O........
	.......................O....O............O..........
	.......................O...............O............
	.........................OO.O.O.......O..O..........
	.........................O....O.........OOO.........
	............................OOO.OO..O...O...O.OO....
	.............................O..OO.O.....O...O..O...
	.....................................OO..O...O......
	..................................O.OO.OO.O..OO...O.
	...............................O.....O...O.......O.O
	................................OO............OO...O
	......................................O.......OO....
	.......................................OOO...OO..O..
	......................................O..O.OOO......
	......................................O....OO.......
	.......................................O............
	..........................................O..O......
	.........................................O..........
	..........................................OO........

:2c/3 Two thirds of the speed of light -- the speed of signals in a 2c/3 wire, or of some against the grain negative spaceship signals in the zebra stripes agar.

:2c/3 wire A wire discovered by Dean Hickerson in March 1997, using his dr search program. It supports signals that travel through the wire diagonally at two thirds of the speed of light.

	......O..O.......................................
	....OOOOOO.......................................
	...O.............................................
	...O..OOOOOO.....................................
	OO.O.O.O....O....................................
	OO.O.O.OOOOOO....................................
	....OO.O.......O.................................
	.......O..OOOOOO.................................
	.......O.O.......................................
	......OO.O..OOOOOO...............................
	.........O.O......O..............................
	.........O.O..OOOOO..............................
	..........OO.O.......O...........................
	.............O..OOOOOO...........................
	.............O.O.................................
	............OO.O..OOOOOO.........................
	...............O.O......O........................
	...............O.O..OOOOO........................
	................OO.O.......O.....................
	...................O..OOOOOO.....................
	...................O.O...........................
	..................OO.O..OOOOOO...................
	.....................O.O......O..................
	.....................O.O..OOOOO..................
	......................OO.O.......O...............
	.........................O..OOOOOO...............
	.........................O.O.....................
	........................OO.O..OOOOOO.............
	...........................O.O......O............
	...........................O.O..OOOOO............
	............................OO.O.......O.........
	...............................O..OOOOOO.........
	...............................O.O...............
	..............................OO.O..OOOOOO.......
	.................................O.O......O......
	.................................O.O..OOOOO......
	..................................OO.O.......O...
	.....................................O..OOOOOO...
	.....................................O.O.........
	....................................OO.O..OOOOOO.
	.......................................O.O......O
	.......................................O.O..OOO.O
	........................................OO.O...O.
	...........................................O..O..
	...........................................O.O...
	..........................................OO.O.O.
	..............................................OO.

Considerable effort has been spent on finding a signal elbow for a 2c/3 signal, since this would by one way to prove Life to be omniperiodic. There is a known 2c/3 wire elbow that is usable in some situations, but it has the drawback that it produces two output signals for each input signal, and so unfortunately can not be used to complete a loop.

In 2017 Martin Grant observed that the 2c/3 signal can be split successfully into two half-signals that can be separated from each other by an arbitrary number of ticks.

:2c/5 spaceship A spaceship travelling at two fifths of the speed of light. The only such spaceships that are currently known travel orthogonally. Examples include 30P5H2V0, 44P5H2V0, 60P5H2V0, and 70P5H2V0. At the time of this writing (August 2017) only 30P5H2V0 and 60P5H2V0 have known glider synthesis recipes.

:2c/7 spaceship A spaceship travelling at two sevenths of the speed of light. The only such spaceships that are currently known travel orthogonally. The first to be found was the weekender, found by David Eppstein in January 2000. See also weekender distaff.

:2 eaters = two eaters

:30P5H2V0 (2c/5 orthogonally, p5) A spaceship discovered by Paul Tooke on 7 December 2000. With just 30 cells, it is currently the smallest known 2c/5 spaceship. A glider synthesis for 30P5H2V0 was found by Martin Grant in January 2015, based on a predecessor by Tanner Jacobi.

	....O........
	...OOO.......
	..OO.OO......
	.............
	.O.O.O.O..O..
	OO...O...OOO.
	OO...O......O
	..........O.O
	........O.O..
	.........O..O
	............O

:31c/240 The rate of travel of the 31c/240 Herschel-pair climber reaction, and Caterpillar-type spaceships based on that reaction. Each Herschel travels 31 cells orthogonally every 240 ticks.

:31c/240 Herschel-pair climber The mechanism defining the rate of travel of the Centipede and shield bug spaceships. Compare pi climber. It consists of a pair of Herschels climbing two parallel chains of blocks. Certain spacings between the block chains allow gliders from each Herschel to delete the extra ash objects produced by the other Herschel. Two more gliders escape, one to each side, leaving only an exact copy of the original block chains, but shifted forward by 9 cells:

	OO.........................................................OO
	OO.........................................................OO
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	.......................................................OOO...
	.......................................................O..O..
	.......................................................O..O..
	......................................................OOOO...
	.......OOO............................................OO.....
	........O............................................O.......
	......OOO.............................................O......
	......................................................O......

:3c/7 spaceship A spaceship travelling at three sevenths of the speed of light. The only such spaceships that are currently known travel orthogonally. The first to be found was the spaghetti monster, found by Tim Coe in June 2016.

:44P5H2V0 (2c/5 orthogonally, p5) A spaceship discovered by Dean Hickerson on 23 July 1991, the first 2c/5 spaceship to be found. Small tagalongs were found by Robert Wainwright and David Bell that allowed the creation of arbitrarily large 2c/5 spaceships. These were the only known 2c/5 spaceships until the discovery of 70P5H2V0 in December 1992.

	....O.....O....
	...OOO...OOO...
	..O..O...O..O..
	.OOO.......OOO.
	..O.O.....O.O..
	....OO...OO....
	O....O...O....O
	.....O...O.....
	OO...O...O...OO
	..O..O...O..O..
	....O.....O....

:45-degree LWSS-to-G = 45-degree MWSS-to-G.

:45-degree MWSS-to-G The following small converter, which accepts an MWSS or LWSS as input and produces an output glider traveling at a 45-degree angle relative to the input direction.

	.........O.OO....O.....
	.........OO.O...O.O....
	................O.O....
	.......OOOOO...OO.OOO..
	......O..O..O........O.
	......OO...OO..OO.OOO..
	...............OO.O....
	......................O
	....................OOO
	...................O...
	...................OO..
	.OOOOO.................
	O....O.................
	.....O.................
	O...O..................
	..O.............OO.....
	...............O..O....
	................OO.....
	........OO.............
	.......O.O.............
	.......O...............
	......OO...............
	...................OO..
	...................O...
	....................OOO
	......................O

:4-8-12 diamond The following pure glider generator.

	....OOOO....
	............
	..OOOOOOOO..
	............
	OOOOOOOOOOOO
	............
	..OOOOOOOO..
	............
	....OOOO....

:4 boats (p2)

	...O....
	..O.O...
	.O.OO...
	O.O..OO.
	.OO..O.O
	...OO.O.
	...O.O..
	....O...

:4F = Fast Forward Force Field. This term is no longer in common use.

:56P6H1V0 (c/6 orthogonally, p6) A 56-cell spaceship discovered by Hartmut Holzwart in 2009, the smallest known c/6 orthogonal spaceship as of this writing (August 2017).

	.....OOO..........OOO.....
	OOO.O.......OO.......O.OOO
	....O...O..O..O..O...O....
	....O.....O....O.....O....
	..........OO..OO..........
	.......O...O..O...O.......
	.......O.O......O.O.......
	........OOOOOOOOOO........
	..........O....O..........
	........O........O........
	.......O..........O.......
	........O........O........

:58P5H1V1 (c/5 diagonally, p5) A spaceship discovered by Matthias Merzenich on 5 September 2010. In terms of its minimum population of 58 cells it is the smallest known c/5 diagonal spaceship. It provides sparks at its trailing edge which can perturb gliders, and this property was used to create the first c/5 diagonal puffers. These sparks also allow the attachment of tagalongs which was used to create the first c/5 diagonal wickstretcher in January 2011.

	....................OO.
	....................OO.
	...................O..O
	................OO.O..O
	......................O
	..............OO...O..O
	..............OO.....O.
	...............O.OOOOO.
	................O......
	.......................
	.......................
	.............OOO.......
	.............O.........
	...........OO..........
	.....OO....O...........
	.....OOO...O...........
	...O....O..............
	...O...O...............
	.......O...............
	..OO.O.O...............
	OO.....O...............
	OO....OO...............
	..OOOO.................

:5c/9 wire A wire discovered by Dean Hickerson in April 1997, using his dr search program. It supports signals that travel through the wire diagonally at five ninths of the speed of light.

	....O.OO............................................
	....OO..O...........................................
	.......O..O.........................................
	..OOOOO.OO.O..O.....................................
	.O..O...O..OOOO.....................................
	.O.OO.O.O.O......O..................................
	OO.O.OOOO.O..OOOOO..................................
	...O......O.O.....OO................................
	OO.O.OOOO.O..O.OO.O.O...............................
	O..O.O..O.OO.O.O.O..O...............................
	..OO..O..O...O.O....O.OO............................
	....OO....OOOO.OO..OO..O............................
	....O...O.O......O...O..............................
	.....OOOO.O.OOOOO.OOO...O...........................
	.........O.O....O.O..OOOO...........................
	.......O...O..O...O.O......O........................
	.......OO..O.O.OOOO.O..OOOOO........................
	..........OO.O......O.O.....OO......................
	.............O.OOOO.O..O.OO.O.O.....................
	.............O.O..O.OO.O.O.O..O.....................
	............OO..O..O...O.O....O.OO..................
	..............OO....OOOO.OO..OO..O..................
	..............O...O.O......O...O....................
	...............OOOO.O.OOOOO.OOO...O.................
	...................O.O....O.O..OOOO.................
	.................O...O..O...O.O......O..............
	.................OO..O.O.OOOO.O..OOOOO..............
	....................OO.O......O.O.....OO............
	.......................O.OOOO.O..O.OO.O.O...........
	.......................O.O..O.OO.O.O.O..O...........
	......................OO..O..O...O.O....O.OO........
	........................OO....OOOO.OO..OO..O........
	........................O...O.O......O...O..........
	.........................OOOO.O.OOOOO.OOO...O.......
	.............................O.O....O.O..OOOO.......
	...........................O...O..O...O.O......O....
	...........................OO..O.O.OOOO.O..OOOOO....
	..............................OO.O......O.O.....OO..
	.................................O.OOOO.O..O.OO.O..O
	.................................O.O..O.OO.O.O.O..OO
	................................OO..O..O...O.O......
	..................................OO....OOOO.OO.....
	..................................O...O.O......O....
	...................................OOOO.O.OOOOO.O...
	.......................................O.O....O.O...
	.....................................O...O..O...OO..
	.....................................OO..O.O.OOO..O.
	........................................OO.O.....O..
	............................................O.OOO...
	.............................................OO.....

:60P5H2V0 (2c/5 orthogonally, p5) A 60-cell spaceship discovered by Tim Coe in May 1996. It was the first non-c/2 orthogonal spaceship to be successfully constructed via glider synthesis.

	.....O.......O.....
	...OO.OO...OO.OO...
	......OO...OO......
	........O.O........
	.O....O.O.O.O....O.
	OOO.....O.O.....OOO
	O.....O.O.O.O.....O
	..O..O..O.O..O..O..
	..OO...OO.OO...OO..
	O.......O.O.......O
	O......OO.OO......O

:67P5H1V1 (c/5 diagonally, p5) A spaceship discovered by Nicolay Beluchenko in July 2006. It was the smallest known c/5 diagonal spaceship until the discovery of 58P5H1V1 in September 2010.

	.....OOO..............
	....O...OO............
	...OO...O.............
	..O.....O.............
	.O.OO....OO...........
	OO..O......O..........
	...OO..O..............
	...OO.OO..............
	....O.................
	.....OOOOO............
	......O..OOO..OO......
	.........O.OO..O.OO...
	.........O...O.O..O...
	..........OOOOO.....O.
	.........O..O..O.....O
	.....................O
	................OOO...
	................O.....
	...............O......
	................OO....

:70P5H2V0 (2c/5 orthogonally, p5) A spaceship discovered by Hartmut Holzwart on 5 December 1992.

	..O............O..
	.O.O..........O.O.
	OO.OO........OO.OO
	OO..............OO
	..O............O..
	..OOOO......OOOO..
	..O..OO....OO..O..
	...OO..O..O..OO...
	....OO.OOOO.OO....
	.....O.O..O.O.....
	......O....O......
	..................
	.....O......O.....
	...OO.OO..OO.OO...
	....O........O....
	....OO......OO....

:7x9 eater A high-clearance eater5 variant that can suppress passing gliders in tight spaces, such as on the inside corner of an R64 Herschel conduit. Like the eater5 and sidesnagger, the 7×9 eater is able to eat gliders coming from two directions, though this ability is not commonly used.

	.O..........
	..O.........
	OOO.........
	............
	......O.....
	.....O......
	.....OOO....
	............
	............
	......O...OO
	.....O.O...O
	.....OO...O.
	.........O..
	.....OOOOO.O
	.....O....OO
	......OOO...
	........O.OO
	.........O.O

:83P7H1V1 = lobster

:86P5H1V1 (c/5 diagonally, p5) A spaceship discovered by Jason Summers on January 8, 2005. It was the smallest known c/5 diagonal spaceship until the discovery of 67P5H1V1 in July 2006.

	.........OOO...........
	........O..............
	.......O...............
	...........OO..........
	........OO.O...........
	..............OOO......
	...........O..OO..OO...
	..O........OO.O...OO...
	.O..O......O..OO.......
	O...O..................
	O...........O..O.......
	O..OO.OOO...O...OO.OO..
	...O...O..OO..O..O.....
	.................OO..O.
	.....OOOO...O.....O...O
	.....OO.O.O..........O.
	.....O.....O......OO...
	...........OOO.........
	......OO.....OO.O......
	......OO...O....O......
	...........O...........
	.............O.O.......
	..............O........

:90-degree kickback See kickback.

:9hd Separated by 9 half diagonals. Specifically used to describe the distance between the two construction lanes in the linear propagator.

:Achim's p144 (p144) This was found (minus the blocks shown below) on a cylinder of width 22 by Achim Flammenkamp in July 1994. Dean Hickerson reduced it to a finite form using figure-8s the same day. The neater finite form shown here - replacing the figure-8s with blocks - was found by David Bell in August 1994. See factory for a use of this oscillator.

	OO........................OO
	OO........................OO
	..................OO........
	.................O..O.......
	..................OO........
	..............O.............
	.............O.O............
	............O...O...........
	............O..O............
	............................
	............O..O............
	...........O...O............
	............O.O.............
	.............O..............
	........OO..................
	.......O..O.................
	........OO..................
	OO........................OO
	OO........................OO

:Achim's p16 (p16) Found by Achim Flammenkamp, July 1994.

	.......OO....
	.......O.O...
	..O....O.OO..
	.OO.....O....
	O..O.........
	OOO..........
	.............
	..........OOO
	.........O..O
	....O.....OO.
	..OO.O....O..
	...O.O.......
	....OO.......

:Achim's p4 (p4) Dave Buckingham found this in a less compact form (using two halves of sombreros) in 1976. The form shown here was found by Achim Flammenkamp in 1988. The rotor is two copies of the rotor of 1-2-3-4, so the oscillator is sometimes called the "dual 1-2-3-4".

	..OO...OO..
	.O..O.O..O.
	.O.OO.OO.O.
	OO.......OO
	..O.O.O.O..
	OO.......OO
	.O.OO.OO.O.
	.O..O.O..O.
	..OO...OO..

:Achim's p5 = pseudo-barberpole

:Achim's p8 (p8) Found by Achim Flammenkamp, July 1994.

	.OO......
	O........
	.O...O...
	.O...OO..
	...O.O...
	..OO...O.
	...O...O.
	........O
	......OO.

:acorn (stabilizes at time 5206) A methuselah found by Charles Corderman.

	.O.....
	...O...
	OO..OOO

:A for all (p6) Found by Dean Hickerson in March 1993.

	....OO....
	...O..O...
	...OOOO...
	.O.O..O.O.
	O........O
	O........O
	.O.O..O.O.
	...OOOO...
	...O..O...
	....OO....

:against the grain A term used for negative spaceships traveling in zebra stripes agar, perpendicular to the stripes, and also for against-the-grain grey ships.

Below is a sample signal, found by Hartmut Holzwart in April 2006, that travels against the grain at 2c/3. This "negative spaceship" travels upward and will quickly reach the edge of the finite patch of stabilized agar shown here.

	...O..O..O..O..O..O..O..O..O..O..O...
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.....................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.....................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.....................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...................................O
	.OOOOOOOOOOOOOOOOO..OOOOOOOOOOOOOOOO.
	.....................................
	.OOOOOOOOOOOOOOO......OOOOOOOOOOOOOO.
	O...............O....O..............O
	.OOOOOOOOOOOOOOOO....OOOOOOOOOOOOOOO.
	.....................................
	.OOOOOOOOOOOOO...OOOO...OOOOOOOOOOOO.
	O.................OO................O
	.OOOOOOOOOOOO............OOOOOOOOOOO.
	.............O..........O............
	.OOOOOOOOOOOOOO........OOOOOOOOOOOOO.
	O..............O......O.............O
	.OOOOOOOOOOOOOOO......OOOOOOOOOOOOOO.
	..........OO....O....O....OO.........
	.OOOOOOO......OOOO..OOOO......OOOOOO.
	O.......O...OO...O..O...OO...O......O
	.OOOOOOO.........O..O.........OOOOOO.
	.........O.....O......O.....O........
	.OOOOOOOOO......O....O......OOOOOOOO.
	O.........O....OO.OO.OO....O........O
	.OOOOOOOOOOO....O....O....OOOOOOOOOO.
	............OO....OO....OO...........
	.OOOOOOO..OOO.O..O..O..O.OOO..OOOOOO.
	O..............OOO..OOO.............O
	.OOOOO......OOO.O....O.OOO......OOOO.
	......O....O..............O....O.....
	.OOOOOO........O......O........OOOOO.
	O......O...OO..O..OO..O..OO...O.....O
	.OOOOOOOO.....O.OO..OO.O.....OOOOOOO.
	.........O..O.OO......OO.O..O........
	.OOOOOOOOO...OO........OO...OOOOOOOO.
	O..........O..............O.........O
	.OOOOOOOOOOOOOOOO....OOOOOOOOOOOOOOO.
	.................OOOO................
	.OOOOOOOOOOOOOOOOO..OOOOOOOOOOOOOOOO.
	O...................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	...O..O..O..O..O..O..O..O..O..O..O...

Holzwart proved in 2006 that 2c/3 is the maximum speed at which signals can move non-destructively against the grain through zebra stripes agar.

:against-the-grain grey ship A grey ship in which the region of density 1/2 consists of lines of ON cells lying perpendicular to the direction in which the spaceship moves. See also with-the-grain grey ship.

:agar Any pattern covering the whole plane that is periodic in both space and time. The simplest (nonempty) agar is the stable one extended by the known spacefillers. For some more examples see chicken wire, houndstooth agar, onion rings, squaredance and Venetian blinds. Tiling the plane with the pattern O......O produces another interesting example: a p6 agar which has a phase of density 3/4, which is the highest yet obtained for any phase of an oscillating pattern.

:aircraft carrier (p1) This is the smallest still life that has more than one island.

	OO..
	O..O
	..OO

:airforce (p7) Found by Dave Buckingham in 1972. The rotor consists of two copies of that used in the burloaferimeter.

	.......O......
	......O.O.....
	.......O......
	..............
	.....OOOOO....
	....O.....O.OO
	...O.OO...O.OO
	...O.O..O.O...
	OO.O...OO.O...
	OO.O.....O....
	....OOOOO.....
	..............
	......O.......
	.....O.O......
	......O.......

:AK47 reaction The following reaction (found by Rich Schroeppel and Dave Buckingham) in which a honey farm predecessor, catalysed by an eater and a block, reappears at another location 47 generations later, having produced a glider and a traffic light. This is the basis of a very small (but pseudo) p94 glider gun found by Paul Callahan in July 1994, and was in 1990 the basis for the Dean Hickerson's construction of the first true p94 gun. (This latter gun was enormous, and has now been superseded by comparatively small Herschel loop guns.)

	.....O....
	....O.O...
	...O...O..
	...O...O..
	...O...O..
	....O.O...
	.....O....
	..........
	..OO......
	...O......
	OOO.....OO
	O.......OO

:AK94 gun The smallest known gun using the AK47 reaction, found by Mike Playle in May 2013 using his Bellman program.

	.......O.......O.......OO.............
	.......OOO.....OOO.....OO.............
	..........O.......O...................
	.........OO......OO................OO.
	..............................OO..O..O
	..............................O.O..OO.
	.................................OO...
	.....O............................O...
	.....OOO..........................O.OO
	........O......................OO.O..O
	.......OO......................OO.OO..
	......................................
	......................................
	.................O....................
	..OO.OO.........O.O..........OO.......
	O..O.OO........O...O.........O........
	OO.O...........O...O..........OOO.....
	...O...........O...O............O.....
	...OO...........O.O...................
	.OO..O.O.........O....................
	O..O..OO..............................
	.OO................OO.................
	...................O..................
	.............OO.....OOO...............
	.............OO.......O...............

:Al Jolson = Jolson

:almosymmetric (p2) Found in 1971.

	....O....
	OO..O.O..
	O.O......
	.......OO
	.O.......
	O......O.
	OO.O.O...
	.....O...

:ambidextrous A type of Herschel transceiver where the receiver can be used in either of two mirror-image orientations. See also chirality.

:anteater A pattern that consumes ants. Matthias Merzenich discovered a c/5 anteater on 15 April 2011. See wavestretcher for details.

:antlers = moose antlers

:ants (p5 wick) The standard form is shown below. It is also possible for any ant to be displaced by one or two cells relative to either or both of its neighbouring ants. Dean Hickerson found fenceposts for both ends of this wick in October 1992 and February 1993. See electric fence, and also wickstretcher.

	OO...OO...OO...OO...OO...OO...OO...OO...OO..
	..OO...OO...OO...OO...OO...OO...OO...OO...OO
	..OO...OO...OO...OO...OO...OO...OO...OO...OO
	OO...OO...OO...OO...OO...OO...OO...OO...OO..

:antstretcher Any wickstretcher that stretches ants. Nicolay Beluchenko and Hartmut Holzwart constructed the following small extensible antstretcher in January 2006:

	......................................................OO.......
	.....................................................OO........
	...............................................OO.....O........
	..............................................OO.....OO........
	................................................O....O.O..OO...
	..................................................OO...OO.OOOO.
	..................................................OO..........O
	..............................................................O
	........................................................O......
	..........................................................OO...
	...............................................................
	..........................................................OOO..
	.........................................................OO..O.
	...............................OO..........................O...
	..............................OO...............................
	...............................O.O...................OOO..O....
	..........................O....OOO...................O..OOO....
	.........................OOOOO.OOO..O.OO................OO.....
	.........................O..OO......O...OO.OO.........OO.OO....
	...................................O....OO...OO.OO.......OO....
	...........................OO..OO.OO..OO.....OO...OO.O.O.......
	...................................O.......OO.....OO...........
	.....................OOO...O.....OO.............OO....O........
	.....................O.....O..O.OO...................O.........
	......................O...OO.O.................................
	.........................OO...O.O..............................
	.............OOO..........O....................................
	.............O.....OOO..OO.....................................
	..............O..OO.OOO.OO.....................................
	................O..........O...................................
	.................O.O.OO....O...................................
	...................OO.O........................................
	.................OO...O.O......................................
	................OO.............................................
	..................O............................................
	...............OO..............................................
	..............OOO..............................................
	.............OO.O..............................................
	............OOOO.O.............................................
	.................OOO...........................................
	..................OO...........................................
	..........OOO.OO...............................................
	.........O...OOO...............................................
	............OOO................................................
	........O.O.O..................................................
	.......OOOO....................................................
	.......O.......................................................
	........OO.....................................................
	.........O..O..................................................
	OO.............................................................
	O.O...OOO......................................................
	O...O....O.....................................................
	...OO..........................................................
	...O.....O.....................................................

:anvil The following induction coil.

	.OOOO.
	O....O
	.OOO.O
	...O.OO

:apgluxe See apgsearch

:apgmera See apgsearch.

:apgnano See apgsearch.

:apgsearch One of several versions of a client-side Ash Pattern Generator soup search script by Adam P. Goucher, for use with Conway's Life and a wide variety of other rules. Development of the original Golly-based Python script started in August 2014. After the addition in 2016 of apgnano (native C++) and apgmera (self-modifying, 256-bit SIMD compatibility), development continues in 2017 with apgluxe (Larger Than Life and Generations rules, more soup shapes). Several customized variants of the Python script have also been created by other programmers, to perform types of searches not supported by Goucher's original apgsearch 1.×.

All of these versions of the search utility work with a "haul" that usually consists of many thousands or millions of random soup patterns. Each soup is run to stability and a detailed object census results is reported to Catagolue. For any rare objects discovered in the ash, the source soup can be easily retrieved from the Catagolue server.

:APPS (c/5 orthogonally, p30) An asymmetric PPS. The same as the SPPS, but with the two halves 15 generations out of phase with one another. Found by Alan Hensel in May 1998.

:ark A pair of mutually stabilizing switch engines. The archetype is Noah's ark. The diagram below shows an ark found by Nick Gotts that takes until generation 736692 to stabilize, and can therefore be considered as a methuselah.

	...........................O....
	............................O...
	.............................O..
	............................O...
	...........................O....
	.............................OOO
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	................................
	OO..............................
	..O.............................
	..O.............................
	...OOOO.........................

:arm A long extension hanging off from the main body of a spaceship or puffer perpendicular to the direction of travel. For a alternate meaning see construction arm.

A lot of known spaceships have multiple arms. This is an artefact of the search methods used to find such spaceships, rather than an indication of what a "typical" spaceship might look like.

:armless A method of generating slow salvos across a wide range of lanes without using a construction arm with a movable elbow. Instead, streams of gliders on two fixed opposing lanes collide with each other to produce clean 90-degree output gliders. Slowing down one of the streams by 8N ticks will move the output lanes of the gliders toward the source of that stream by N full diagonals. This construction method was used to create the supporting slow salvos in the half-baked knightships, and also in the Parallel HBK gun.

:ash The stable or oscillating objects left behind when a chaotic reaction stabilizes, or "burns out". Experiments show that for random soups with moderate initial densities (say 0.25 to 0.5) the resulting ash has a density of about 0.0287. (This is, of course, based on what happens in finite fields. In infinite fields the situation may conceivably be different in the long run because of the effect of certain initially very rare objects such as replicators.)

:aVerage (p5) Found by Dave Buckingham, 1973. The average number of live rotor cells is five (V), which is also the period.

	...OO........
	....OOO......
	..O....O.....
	.O.OOOO.O....
	.O.O....O..O.
	OO.OOO..O.O.O
	.O.O....O..O.
	.O.OOOO.O....
	..O....O.....
	....OOO......
	...OO........

:B = B-heptomino

:B29 (c/4 diagonally, p4) The following spaceship, found by Hartmut Holzwart in April 2004.

	.......OOO.......
	.......O.........
	OOO......O.......
	O......O.O.......
	.O....OO.OOOO....
	...OOOO.OOOOO.OO.
	....OO.......OO.O

:B-52 bomber The following p104 double-barrelled glider gun. It uses a B-heptomino and emits one glider every 52 generations. It was found by Noam Elkies in March 1996, except that Elkies used blockers instead of molds, the improvement being found by David Bell later the same month.

	.OO....................................
	.OO.................O..................
	...................O.O............O.O..
	....................O............O.....
	OO.......OO.......................O..O.
	OO.O.....OO.......................O.O.O
	...O.......................O.......O..O
	...O.......................OO.......OO.
	O..O.................OO.....O..........
	.OO..................O.................
	.....................OOO...............
	....................................OO.
	....................................OO.
	.OO....................................
	O..O...................................
	O.O.O................O.O....OO.....OO..
	.O..O.................OO....OO.....OO.O
	.....O............O...O...............O
	..O.O............O.O..................O
	..................O................O..O
	....................................OO.

:B60 A Herschel conduit discovered by Michael Simkin in 2015 using his search program, CatForce. It is one of two known Blockic elementary conduits. After 60 ticks, it produces a Herschel rotated 180 degrees at (×,y) relative to the input. It can most easily be connected to another B60 conduit, producing a closed loop, the Simkin glider gun.

	O...........OO.....OO
	OOO.........OO.....OO
	..O..................
	..O............OO....
	...............OO....
	.....................
	.....................
	.....................
	.....................
	......O..............
	......O.O............
	......OOO............
	........O............

:babbling brook Any oscillator whose rotor consists of a string of cells each of which is adjacent to exactly two other rotor cells, except for the endpoints which are adjacent to only one other rotor cell. Compare muttering moat. Examples include the beacon, the great on-off, the light bulb and the spark coil. The following less trivial example (by Dean Hickerson, August 1997) is the only one known with more than four cells in its rotor. It is p4 and has a 6-cell rotor.

	.......O........
	.....OOO....OO..
	....O...OO..O...
	.O..O.OO..O.O...
	O.O.O....OO..OO.
	.OO..OO....O.O.O
	...O.O..OO.O..O.
	...O..OO...O....
	..OO....OOO.....
	........O.......

:backrake Another term for a backwards rake. A p8 example by Jason Summers is shown below. See total aperiodic for a p12 example.

	.....OOO...........OOO.....
	....O...O.........O...O....
	...OO....O.......O....OO...
	..O.O.OO.OO.....OO.OO.O.O..
	.OO.O....O.OO.OO.O....O.OO.
	O....O...O..O.O..O...O....O
	............O.O............
	OO.......OO.O.O.OO.......OO
	............O.O............
	......OOO.........OOO......
	......O...O.........O......
	......O.O....OOO...........
	............O..O....OO.....
	...............O...........
	...........O...O...........
	...........O...O...........
	...............O...........
	............O.O............

:backward glider A glider which moves at least partly in the opposite direction to the puffer(s) or spaceship(s) under consideration.

:bait An object in a converter, usually a small still life, that is temporarily destroyed by an incoming signal, but in such a way that a usable output signal is produced. In general such a converter produces multiple output signals (or a signal splitter is added) and one branch of the output is routed to a factory mechanism that rebuilds the bait object so that the converter can be re-used.

:baker (c p4 fuse) A fuse by Keith McClelland.

	..............OO
	.............O.O
	............O...
	...........O....
	..........O.....
	.........O......
	........O.......
	.......O........
	......O.........
	.....O..........
	....O...........
	...O............
	OOO.............
	.O..............

:baker's dozen (p12) A loaf hassled by two blocks and two caterers. The original form (using p4 and p6 oscillators to do the hassling) was found by Robert Wainwright in August 1989.

	OO.........OO..........
	OOOO.O.....OO..........
	O.O..OOO...............
	...........O...........
	....OO....O.O..........
	....O.....O..O....O....
	...........OO....OO....
	.......................
	...............OOO..O.O
	..........OO.....O.OOOO
	..........OO.........OO

:bakery (p1) A common formation of two bi-loaves.

	....OO....
	...O..O...
	...O.O....
	.OO.O...O.
	O..O...O.O
	O.O...O..O
	.O...O.OO.
	....O.O...
	...O..O...
	....OO....

:banana spark A three-bit polyplet spark used in glider construction. It can be used to turn a glider 90 degrees:

	..O....
	O.O....
	.OO....
	....OO.
	......O

:barberpole Any p2 oscillator in the infinite sequence bipole, tripole, quadpole, pentapole, hexapole, heptapole ... (It wasn't my idea to suddenly change from Latin to Greek.) This sequence of oscillators was found by the MIT group in 1970. The term is also used (usually in the form "barber pole") to describe other extensible sections of oscillators or spaceships, especially those (usually of period 2) in which all generations look alike except for a translation and/or rotation/reflection.

:barberpole intersection = quad

:barber's pole = barberpole

:barge (p1)

	.O..
	O.O.
	.O.O
	..O.

:basic shuttle = queen bee shuttle

:beacon (p2) The third most common oscillator. Found by Conway, March 1970.

	OO..
	O...
	...O
	..OO

:beacon maker (c p8 fuse)

	..............OO
	.............O.O
	............O...
	...........O....
	..........O.....
	.........O......
	........O.......
	.......O........
	......O.........
	.....O..........
	....O...........
	...O............
	OOO.............
	..O.............
	..O.............

:beehive (p1) The second most common still life.

	.OO.
	O..O
	.OO.

:beehive and dock (p1)

	...OO.
	..O..O
	...OO.
	......
	.OOOO.
	O....O
	OO..OO

:beehive on big table = beehive and dock

:beehive pusher = hivenudger

:beehive wire See lightspeed telegraph.

:beehive with tail (p1)

	.OO...
	O..O..
	.OO.O.
	....O.
	....OO

:Bellman A program for searching catalytic reactions, developed by Mike Playle, which successfully found the Snark.

:belly spark The spark of a MWSS or HWSS other than the tail spark.

:bent keys (p3) Found by Dean Hickerson, August 1989. See also odd keys and short keys.

	.O........O.
	O.O......O.O
	.O.OO..OO.O.
	....O..O....
	....O..O....

:BFx59H One of the earliest and most remarkable converters, discovered by Dave Buckingham in July 1996. In 59 generations it transforms a B-heptomino into a clean Herschel with very good clearance, allowing easy connections to other conduits. It forms the final stage of many of the known composite conduits, including the majority of the original sixteen Herschel conduits. Here a ghost Herschel marks the output location:

	.OO.....................
	..O.....................
	.O......................
	.OO.....................
	........................
	........................
	........................
	........................
	........................
	O...OO...............O..
	OO..OO...............O..
	.OO..................OOO
	.O.....................O
	O.......................

:B-heptomino (stabilizes at time 148) This is a very common pattern. It often arises with the cell at top left shifted one space to the left, which does not affect the subsequent evolution. B-heptominoes acquired particular importance in 1996 due to Dave Buckingham's work on B tracks - see in particular My Experience with B-heptominos in Oscillators.

	O.OO
	OOO.
	.O..

:B-heptomino shuttle = twin bees shuttle

:bi-block (p1) The smallest pseudo still life.

	OO.OO
	OO.OO

:bi-boat = boat-tie

:biclock The following pure glider generator consisting of two clocks.

	..O....
	OO.....
	..OO...
	.O...O.
	...OO..
	.....OO
	....O..

:big beacon = figure-8

:big fish = HWSS

:big glider (c/4 diagonally, p4) This was found by Dean Hickerson in December 1989 and was the first known diagonal spaceship other than the glider.

	...OOO............
	...O..OOO.........
	....O.O...........
	OO.......O........
	O.O....O..O.......
	O........OO.......
	.OO...............
	.O..O.....O.OO....
	.O.........OO.O...
	...O.O......OO..O.
	....OO.O....OO...O
	........O.......O.
	.......OOOO...O.O.
	.......O.OO...OOOO
	........O...OO.O..
	.............OO...
	.........O.OOO....
	..........O..O....

:big S (p1)

	....OO.
	...O..O
	...O.OO
	OO.O...
	O..O...
	.OO....

:big table = dock

:billiard table = billiard table configuration.

:billiard table configuration Any oscillator in which the rotor is enclosed within the stator. Examples include airforce, cauldron, clock II, Hertz oscillator, negentropy, pinwheel, pressure cooker and scrubber.

:bi-loaf This term has been used in at least three different senses. A bi-loaf can be half a bakery:

	.O.....
	O.O....
	O..O...
	.OO.O..
	...O.O.
	...O..O
	....OO.
or it can be the following much less common still life:
	..O....
	.O.O...
	O..O...
	.OO.OO.
	...O..O
	...O.O.
	....O..
or the following pure glider generator:
	..O.
	.O.O
	O..O
	.OO.
	O..O
	O.O.
	.O..

:bipole (p2) The barberpole of length 2.

	OO...
	O.O..
	.....
	..O.O
	...OO

:bi-pond (p1)

	.OO....
	O..O...
	O..O...
	.OO.OO.
	...O..O
	...O..O
	....OO.

:bi-ship = ship-tie

:bit A live cell.

:biting off more than they can chew (p3) Found by Peter Raynham, July 1972.

	O...........
	OOO.........
	...O........
	..OO........
	...OO.......
	....OO......
	...O..O.....
	...O..OO....
	....OO.OOO..
	........O.O.
	..........O.
	..........OO

:Black&White = Immigration

:blasting cap The pi-heptomino (after the shape at generation 1). A term used at MIT and still occasionally encountered.

:blinker (p2) The smallest and most common oscillator. Found by Conway, March 1970.

	OOO

:blinker puffer Any puffer whose output is blinkers. However, the term is particularly used for p8 c/2 puffers. The first such blinker puffer was found by Robert Wainwright in 1984, and was unexpectedly simple:

	...O.....
	.O...O...
	O........
	O....O...
	OOOOO....
	.........
	.........
	.........
	.OO......
	OO.OOO...
	.OOOO....
	..OO.....
	.........
	.....OO..
	...O....O
	..O......
	..O.....O
	..OOOOOO.
Since then many more blinker puffers have been found. The following one was found by David Bell in 1992 when he was trying to extend an x66:
	.............OOO.
	............OOOOO
	...........OO.OOO
	............OO...
	.................
	.................
	.........O.O.....
	..O.....O..O.....
	.OOOOO...O.O.....
	OO...OO.OO.......
	.O.......O.......
	..OO..O..O.......
	..........O......
	..OO..O..O.......
	.O.......O.......
	OO...OO.OO.......
	.OOOOO...O.O.....
	..O.....O..O.....
	.........O.O.....
	.................
	.................
	............OO...
	...........OO.OOO
	............OOOOO
	.............OOO.
The importance of this larger blinker puffer (and others like it), is that the engine which produces the blinker output is only p4. The blinker row produced by the puffer can easily be ignited, and burns cleanly with a speed of 2c/3. When the burning catches up to the engine, it causes a phase change in the puffer. This fact allows p8 blinker puffers to be used to construct rakes of all periods which are large multiples of four.

:blinker pull The following glider/blinker collision, which moves a blinker (-1,3) toward the glider source:

	OOO.
	....
	....
	....
	.OOO
	.O..
	..O.

:blinkers bit pole (p2) Found by Robert Wainwright, June 1977.

	.....OO
	OOO.O.O
	.......
	.O.O..O
	O....O.
	OO...O.

:blinker ship A growing spaceship in which the wick consists of a line of blinkers. An example by Paul Schick based on his Schick engine is shown below. Here the front part is p12 and moves at c/2, while the back part is p26 and moves at 6c/13. Every 156 generations 13 blinkers are created and 12 are destroyed, so the wick becomes one blinker longer.

	..........OOOO.............
	..........O...O............
	..........O................
	.OO........O..O............
	OO.OO......................
	.OOOO...O..................
	..OO...O.OO........O....OOO
	......O...O........O....O.O
	..OO...O.OO........O....OOO
	.OOOO...O..................
	OO.OO......................
	.OO........O..O............
	..........O................
	..........O...O............
	..........OOOO.............

:block (p1) The most common still life.

	OO
	OO

:blockade (p1) A common formation of four blocks. The final form of lumps of muck.

	OO.....................
	OO.....................
	.......................
	.......................
	.OO.................OO.
	.OO.................OO.
	.......................
	.......................
	.....................OO
	.....................OO

:block and dock (p1)

	...OO.
	...OO.
	......
	.OOOO.
	O....O
	OO..OO

:block and glider (stabilizes at time 106)

	OO..
	O.O.
	..OO

:blocker (p8) Found by Robert Wainwright. See also filter.

	......O.O.
	.....O....
	OO..O....O
	OO.O..O.OO
	....OO....

:Blockic Adjective for constellations consisting entirely of blocks. It's possible to arrange blocks in a way that can be triggered by a single glider to produce any glider constructible pattern. See seed.

:block on big table = block and dock

:block on table (p1)

	..OO
	..OO
	....
	OOOO
	O..O

:block pull The following glider/block collision, which moves a block (2,1) toward the glider source:

	OO.
	OO.
	...
	...
	...
	...
	OOO
	O..
	.O.

:block pusher A pattern emitting streams of gliders which can repeatedly push a block further away. This can be used as part of a sliding block memory.

The following pattern, in which three gliders push a block one cell diagonally, is an example of how a block pusher works.

	...................O.O
	...................OO.
	....................O.
	......................
	......................
	......................
	...O..................
	..O...................
	..OOO.................
	......................
	......................
	......................
	......................
	OO...O................
	OO...O.O..............
	.....OO...............

A universal construction elbow recipe library is also likely to contain one or more block-pushing reactions, since blocks are commonly used as elbows.

:blom (stabilizes at time 23314) The following methuselah, found by Dean Hickerson in July 2002.

	O..........O
	.OOOO......O
	..OO.......O
	..........O.
	........O.O.

:blonk A block or a blinker. This term is mainly used in the context of sparse Life and was coined by Rich Schroeppel in September 1992.

:blonker (p6) The following oscillator, found by Nicolay Beluchenko in April 2004.

	O..OO....O..
	OO..O.OO.O..
	....O.O.....
	.....OO.....
	.......O....
	.......O...O
	.........O.O
	..........O.

:boat (p1) The only 5-cell still life.

	OO.
	O.O
	.O.

:boat-bit A binary digit represented by the presence of a boat next to a snake (or other suitable object, such as an aircraft carrier). The bit can be toggled by a glider travelling along a certain path. A correctly timed glider on a crossing path can detect whether the transition was from 1 to 0 (in which case the crossing glider is deleted) or from 0 to 1 (in which case it passes unharmed). Three gliders therefore suffice for a non-destructive read. The mechanisms involved are shown in the diagram below. Here the bit is shown in state 0. It is about to be set to 1 and then switched back to 0 again. The first crossing glider will survive, but the second will be destroyed.

	......O..................
	.......O.................
	.....OOO.................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	.........................
	................O........
	..............O.O........
	..........OO...OO........
	...........OO............
	..........O..........O.OO
	.....................OO.O
	.........................
	.........................
	.........................
	.........................
	.........................
	.O.......................
	.OO......................
	O.O......................

In January 1997 David Bell found a method of reading the bit while setting it to 0. A MWSS is fired at the boat-bit. If it is already 0 (absent) then the MWSS passes unharmed, but if it is 1 (present) then the boat and the MWSS are destroyed and, with the help of an eater1, converted into a glider which travels back along exactly the same path that is used by the gliders that toggle the boat-bit.

	................................................O........
	................................................OOO......
	...................................................O.....
	..................................................OO.....
	.........................................................
	.........................................................
	.........................................................
	.........................................................
	..O......................................................
	O...O..............................................O.....
	.....O..............................OOOOO...........O....
	O....O.............................O....O.........OOO....
	.OOOOO..................................O................
	...................................O...O.................
	.....................................O...................
	.........................................................
	.........................................................
	.......................................................OO
	........................................................O
	.......................................................O.
	.......................................................OO
There are many other equivalent methods based on alternate incoming test signals.

:boat maker (c p4 fuse)

	................OO
	...............O.O
	..............O...
	.............O....
	............O.....
	...........O......
	..........O.......
	.........O........
	........O.........
	.......O..........
	......O...........
	.....O............
	OOOOO.............
	....O.............
	....O.............
	....O.............
	....O.............

:boat on boat = boat-tie

:boat-ship-tie = ship tie boat

:boatstretcher See tubstretcher.

:boat-tie (p1) A 10-cell still life consisting of two boats placed tip-to-tip. The name is a pun on "bow tie".

	.O....
	O.O...
	.OO...
	...OO.
	...O.O
	....O.

:bobsled = switch engine channel.

:boojum reflector (p1) Dave Greene's name for the following 180-degree glider reflector which he found in April 2001, winning $100 bounties offered by Alan Hensel and Dietrich Leithner. The name is taken from Lewis Carroll's _The Hunting of the Snark_, referring to the fact that a small 90-degree stable reflector was really what was wanted. 180-degree reflectors are relatively undesirable and have limited use in larger circuitry constructions.

The boojum reflector was the smallest and fastest known stable reflector until the discovery of the rectifier in 2009, followed by the Snark in 2013.

	....O.O......OO.............................
	.....OO......OO.............................
	.....O......................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	........................................O...
	.......................................O.O..
	.......................................O.O..
	....................OO................OO.OO.
	....................OO......................
	......................................OO.OO.
	..OO..................................OO.O..
	.O.O.......................................O
	.O........................................OO
	OO..........................................
	............................................
	..................................OO........
	..................................OO....OO..
	...........OO...........................O.O.
	..........O.O.............................O.
	..........O...............................OO
	.........OO.......................OO........
	..................................OO........
	............................................
	............................................
	.............................O..............
	............................O.O.............
	.............................O..............

:bookend The following induction coil. It is generation 1 of century.

	..OO
	O..O
	OOO.

:bookends (p1)

	OO...OO
	O.O.O.O
	..O.O..
	.OO.OO.

:boss (p4) Found by Dave Buckingham, 1972.

	.....O.....
	....O.O....
	....O.O....
	...OO.OO...
	..O.....O..
	.O.O.O.O.O.
	.O.O...O.O.
	OO.O...O.OO
	O..O.O.O..O
	..O.....O..
	...OO.OO...
	....O.O....
	....O.O....
	.....O.....

:bottle (p8) Found by Achim Flammenkamp in August 1994. The name is a back-formation from ship in a bottle.

	....OO......OO....
	...O..O....O..O...
	...O.O......O.O...
	.OO..OOO..OOO..OO.
	O......O..O......O
	O.OO..........OO.O
	.O.O..........O.O.
	...OO........OO...
	..................
	..................
	...OO........OO...
	.O.O..........O.O.
	O.OO..........OO.O
	O......O..O......O
	.OO..OOO..OOO..OO.
	...O.O......O.O...
	...O..O....O..O...
	....OO......OO....

:bounding box The smallest rectangular array of cells that contains the whole of a given pattern. For oscillators and guns this usually is meant to include all phases of the pattern, but in the case of guns, the outgoing stream(s) are excluded. The bounding box is one of the standard ways to measure the size of an object; the other standard metric is the population.

:bow tie = boat-tie

:brain (c/3 orthogonally, p3) Found by David Bell, May 1992.

	.OOO.........OOO.
	O.O.OO.....OO.O.O
	O.O.O.......O.O.O
	.O.OO.OO.OO.OO.O.
	.....O.O.O.O.....
	...O.O.O.O.O.O...
	..OO.O.O.O.O.OO..
	..OOO..O.O..OOO..
	..OO..O...O..OO..
	.O....OO.OO....O.
	.O.............O.

:breeder Any pattern whose population grows at a quadratic rate, although it is usual to exclude spacefillers. It is easy to see that this is the fastest possible growth rate.

The term is also sometimes used to mean specifically the breeder created by Bill Gosper's group at MIT, which was the first known pattern exhibiting superlinear growth.

There are four common types of breeder, known as MMM, MMS, MSM and SMM (where M=moving and S=stationary). Typically an MMM breeder is a rake puffer, an MMS breeder is a puffer producing puffers which produce stationary objects (still lifes and/or oscillators), an MSM breeder is a gun puffer and an SMM breeder is a rake gun. There are, however, less obvious variants of these types. Other less common breeder categories (SSS, hybrid MSS/MSM, etc.) can be created with some difficulty, based on universal constructor technology; see Pianola breeder.

The original breeder was of type MSM (a p64 puffer puffing p30 glider guns). The known breeder with the smallest initial population is the metacatacryst.

:bridge A term used in naming certain still lifes (and the stator part of certain oscillators). It indicates that the object consists of two smaller objects joined edge to edge, as in snake bridge snake.

:broken lines A pattern constructed by Dean Hickerson in May 2005 which produces complex broken lines of gliders and blocks.

:broth = soup

:BRx46B A Spartan elementary conduit discovered by Michael Simkin on 25 April 2016, one of the relatively few known conduits that can move a B-heptomino input to a B-heptomino output without an intervening Herschel stage.

	...........OO
	..OO.......OO
	..OO.........
	.............
	.............
	O..........O.
	.O........O.O
	.OO.......O.O
	OO.........O.
	O............

:BTC = billiard table configuration

:B track A track for B-heptominoes. A B-heptomino becomes a Herschel plus a block in twenty generations, so this term was nearly synonymous with Herschel track until the discovery of elementary conduits that convert a B directly to another B, or to some other non-Herschel signal output. See for example BRx46B.

:buckaroo A queen bee shuttle stabilized at one end by an eater in such a way that it can turn a glider, as shown below. This was found by Dave Buckingham in the 1970s. The name is due to Bill Gosper.

	..O.....................
	O.O.....................
	.OO.....................
	...........O............
	.........O.O............
	........O.O.............
	.......O..O...........OO
	........O.O...........OO
	...OO....O.O............
	..O.O......O............
	..O.....................
	.OO.....................

:bullet heptomino Generation 1 of the T-tetromino.

	.O.
	OOO
	OOO

:bumper A periodic colour-preserving glider reflector discovered by Tanner Jacobi on 6 April 2016. See p4 bumper, p5 bumper, p6 bumper, p7 bumper, p8 bumper, p9 bumper, p15 bumper, and p22 bumper.

:bun The following induction coil. By itself this is a common predecessor of the honey farm. See also cis-mirrored R-bee.

	.OO.
	O..O
	.OOO

:bunnies (stabilizes at time 17332) This is a parent of rabbits and was found independently by Robert Wainwright and Andrew Trevorrow.

	O.....O.
	..O...O.
	..O..O.O
	.O.O....

:burloaf = loaf

:burloaferimeter (p7) Found by Dave Buckingham in 1972. See also airforce.

	....OO....
	.....O....
	....O.....
	...O.OOO..
	...O.O..O.
	OO.O...O.O
	OO.O....O.
	....OOOO..
	..........
	....OO....
	....OO....

:bushing That part of the stator of an oscillator which is adjacent to the rotor. Compare casing.

:butterfly The following pattern, or the formation of two beehives that it evolves into after 33 generations. (Compare teardrop, where the beehives are five cells closer together.)

	O...
	OO..
	O.O.
	.OOO

:Bx125 An elementary conduit, one of the original sixteen Herschel conduits, discovered by Paul Callahan in November 1998. After 125 ticks, it produces an inverted Herschel rotated 180 degrees at (-9, -17) relative to the input. Its recovery time is 166 ticks. A ghost Herschel in the pattern below marks the output location:

	...........................O..........
	..O.......................O.O.........
	..O.......................O.O.........
	OOO.........OO...........OO.OOO.......
	O...........OO.................O......
	.........................OO.OOO.......
	.........................OO.O.........
	......................................
	......................................
	......................................
	......................................
	......................................
	......................................
	......................................
	......................................
	....................................OO
	....................................OO
	......................................
	.........O............................
	.........O.O..........................
	.........OOO..........................
	...........O..........................
	......................................
	.......................OO.............
	.......................O..............
	........................OOO...........
	..........................O...........

:Bx222 A composite conduit, one of the original sixteen Herschel conduits, discovered by Paul Callahan in October 1998. It is made up of three elementary conduits, HF95P + PB68B + BFx59H. After 222 ticks, it produces a backward-traveling inverted Herschel at (6, -16) relative to the input. Its recovery time is 271 ticks. A ghost Herschel in the pattern below marks the output location:

	.............O............................
	....OO.....OOO.......OO...................
	.....O....O..........O....................
	.....O.O...O..........O...................
	......O.O...O........OO...................
	.......O...OO.................O......O....
	............................OOO.....O.O...
	...........................O........O.O...
	...........................OO......OO.OOO.
	.........................................O
	..O...............OO...............OO.OOO.
	..O...............OO...............OO.O...
	OOO.......................................
	O.........................................
	..........................................
	..........................................
	........................................OO
	........................................O.
	......................................O.O.
	......................................OO..
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	......O...................................
	......O.O.................................
	......OOO.................................
	........O....................OO...........
	.............................O............
	..................OO..........O...........
	..................OO..OO.....OO...........
	......................O.O.................
	........................O.................
	........................OO................

:by flops (p2) Found by Robert Wainwright.

	...O..
	.O.O..
	.....O
	OOOOO.
	.....O
	.O.O..
	...O..

:c = speed of light

:c/10 spaceship A spaceship travelling at one tenth of the speed of light. The first such spaceship to be discovered was the orthogonally traveling copperhead, found by 'zdr' on 5 March 2016. Simon Ekstrom found the related fireship two weeks later. A Caterloopillar can theoretically be configured to move at c/10, but there are technical difficulties with speeds of the form 4×+2, and as of August 2017 this has not been done in practice.

:c/12 spaceship A spaceship travelling at one twelfth of the speed of light. The only diagonal spaceships that are currently known to move at this speed are the Corderships. An orthogonal Caterloopillar has been configured to move at c/12.

:c/2 spaceship A spaceship travelling at half the speed of light. Such spaceships necessarily move orthogonally. The first to be discovered was the LWSS. For other examples see Coe ship, ecologist, flotilla, hammerhead, hivenudger, HWSS, MWSS, puffer train, puff suppressor, pushalong, Schick engine, sidecar, still life tagalong and x66.

:c/3 spaceship A spaceship travelling at one third of the speed of light. All known c/3 spaceships travel orthogonally, and the first was found in August 1989 by Dean Hickerson. For further examples see brain, dart, edge-repair spaceship, fly, turtle and wasp. A spaceship moving diagonally at an angle of 45 degree cannot travel at a speed of c/3, but it is likely that c/3 knightships exist, though none have yet been found.

:c/4 spaceship A spaceship travelling at one quarter of the speed of light. The first such spaceship to be discovered was, of course, the glider, and this remained the only known example until December 1989, when Dean Hickerson found the first orthogonal example, 119P4H1V0, and also a new diagonal example (the big glider). For other examples see B29, Canada goose, crane, Enterprise, edge-repair spaceship (third pattern), non-monotonic, Orion, quarter, sparky, swan and tagalong. It is known that c/4 is the fastest possible speed for a (45-degree) diagonal spaceship.

:c/5 spaceship A spaceship travelling at one fifth of the speed of light. The first such spaceship to be discovered was the snail, found by Tim Coe in January 1996. The first diagonally moving example, 295P5H1V1, was found by Jason Summers in November 2000. In January 2005, Summers found the smaller diagonal specimen shown below.

	..........OO..........
	.........O..O.........
	........OO............
	.........O.OO.........
	..........O.OOO.......
	..........OO.OOO......
	............O....OO...
	............OOO....OO.
	..O.........O.O.......
	.OOO........O..O......
	O...OO................
	O..O.O.......OO.O..O..
	.O.OO.OOOO...O...OOOO.
	....OO.O...OO.......O.
	....OO.OO..O.........O
	.....O...O........O.OO
	...........O.......O..
	......O.....O......O..
	......O.....O..O......
	.......O...OO...OO....
	.......O....OO.O......
	..............OO......
A Caterloopillar has also been configured to move at c/5.

:c/6 spaceship A spaceship travelling at one sixth of the speed of light. The first such spaceship to be discovered was the dragon, found by Paul Tooke in April 2000. The first diagonally moving example was the seal, found by Nicolay Beluchenko in September 2005. Another orthogonal c/6 spaceship, found by Paul Tooke in March 2006, is shown below.

	..O..............O..................................O.....
	O..O..OOO.......O.OOOO...............OO...........OO.O....
	O..O............OOO.O.O.........O.....O.......O...O.......
	.O.O..O.....................OOO..O.O.OOO.....O.O.O....O...
	..OO......O....O................OOOOOO..O..O...O...O..O...
	.O.O...OO.....O...OO......OO.OO..O..OO..O.O.OO..O.........
	..O.....O.OO..O...OO......OO....O.O.O..O..O.O.O......OO..O
	..O....OOO..O.........OOO.......OOO.O.OO.....O.......OOO.O
	............OOOOOOOOO...O........OO.OOO...OOOO.........O.O
	..........................................................
	............OOOOOOOOO...O........OO.OOO...OOOO.........O.O
	..O....OOO..O.........OOO.......OOO.O.OO.....O.......OOO.O
	..O.....O.OO..O...OO......OO....O.O.O..O..O.O.O......OO..O
	.O.O...OO.....O...OO......OO.OO..O..OO..O.O.OO..O.........
	..OO......O....O................OOOOOO..O..O...O...O..O...
	.O.O..O.....................OOO..O.O.OOO.....O.O.O....O...
	O..O............OOO.O.O.........O.....O.......O...O.......
	O..O..OOO.......O.OOOO...............OO...........OO.O....
	..O..............O..................................O.....
A Caterloopillar can theoretically be configured to move at c/6, but there are technical difficulties with speeds of the form 4×+2, and as of August 2017 this has not been done in practice.

:c/7 spaceship A spaceship travelling at one seventh of the speed of light. The first such spaceship to be discovered was the diagonally traveling lobster, found by Matthias Merzenich in August 2011. The first known orthogonal c/7 spaceship was the loafer, discovered by Josh Ball in February 2013. A Caterloopillar has been configured to move at c/7.

:CA = cellular automaton

:caber tosser Any pattern whose population is asymptotic to c.log(t) for some constant c, and which contains a glider (or other spaceship) bouncing between a slower receding spaceship and a fixed reflector which emits a spaceship (in addition to the reflected one) whenever the bouncing spaceship hits it.

As the receding spaceship gets further away the bouncing spaceship takes longer to complete each cycle, and so the extra spaceships emitted by the reflector are produced at increasingly large intervals. More precisely, if v is the speed of the bouncing spaceship and u the speed of the receding spaceship, then each interval is (v+u)/(v-u) times as long as the previous one. The population at time t is therefore n.log(t)/log((v+u)/(v-u)) + O(1), where n is the population of one of the extra spaceships (assumed constant).

The first caber tosser was built by Dean Hickerson in May 1991.

:Callahan G-to-H A stable glider reflector and glider-to-Herschel converter discovered by Paul Callahan in November 1998. Its recovery time is 575 ticks. The initial stage converts two gliders into a Herschel. A ghost Herschel in the pattern below marks the output location:

	....O.........O...................
	....OOO.....OOO...................
	.O.....O...O......................
	..O...OO...OO.....................
	OOO...............................
	.........O........................
	........O.O.......................
	........O.O.......................
	.........O........................
	...............................O..
	...............................O..
	....................OO.........OOO
	..............OO....OO...........O
	........OO...OO...................
	.......O..O....O..................
	..OO....OO........................
	.O.O..............................
	.O................................
	OO................................
	..........OO......................
	..........O.......................
	...........OOO....................
	.............O....................

The glider from the southeast can be supplied by a Fx77 + L112 + Fx77 Herschel track, or by reflecting the output Herschel's FNG as in the p8 G-to-H. See also Silver reflector, Silver G-to-H.

:Cambridge pulsar CP 48-56-72 = pulsar (The numbers refer to the populations of the three phases. The Life pulsar was indeed discovered at Cambridge, like the first real pulsar a few years earlier.)

        ..OOO...OOO..
        .............
        O....O.O....O
        O....O.O....O
        O....O.O....O
        ..OOO...OOO..
        .............
        ..OOO...OOO..
        O....O.O....O
        O....O.O....O
        O....O.O....O
        .............
        ..OOO...OOO..

:Canada goose (c/4 diagonally, p4) Found by Jason Summers, January 1999. It consists of a glider plus a tagalong.

        OOO..........
	O.........OO.
	.O......OOO.O
	...OO..OO....
	....O........
	........O....
	....OO...O...
	...O.O.OO....
	...O.O..O.OO.
	..O....OO....
	..OO.........
	..OO.........
At the time of its discovery the Canada goose was the smallest known diagonal spaceship other than the glider, but this record has since been beaten, first by the second spaceship shown under Orion, and more recently by quarter.

:candelabra (p3) By Charles Trawick. See also the note under cap.

	....OO....OO....
	.O..O......O..O.
	O.O.O......O.O.O
	.O..O.OOOO.O..O.
	....O.O..O.O....
	.....O....O.....

:candlefrobra (p3) Found by Robert Wainwright in November 1984.

	.....O....
	.O.OO.O.OO
	O.O...O.OO
	.O....O...
	.....OO...
The following diagram shows that a pair of these can act in some ways like killer toads. See also snacker.
	....O...........O....
	OO.O.OO.O...O.OO.O.OO
	OO.O...O.O.O.O...O.OO
	...O....O...O....O...
	...OO...........OO...
	.....................
	.....................
	.........OOO.........
	.........O..O........
	.........O...........
	.........O...O.......
	.........O...O.......
	.........O...........
	..........O.O........

:canoe (p1)

	...OO
	....O
	...O.
	O.O..
	OO...

:cap The following induction coil. It can also be easily be stabilized to form a p3 oscillator - see candelabra for a slight variation on this.

	.OO.
	O..O
	OOOO

:carnival shuttle (p12) Found by Robert Wainwright in September 1984 (using MW emulators at the end, instead of the monograms shown here).

	.................................O...O
	OO...OO..........................OOOOO
	.O.O.O...O..O......OO...O..O.......O..
	.OO.OO..OO...OO....OO..OO...OO....O.O.
	.O.O.O...O..O......OO...O..O.......O..
	OO...OO..........................OOOOO
	.................................O...O

:carrier = aircraft carrier

:casing That part of the stator of an oscillator which is not adjacent to the rotor. Compare bushing.

:catacryst A 58-cell quadratic growth pattern found by Nick Gotts in April 2000. This was formerly the smallest known pattern with superlinear growth, but has since been superseded by the related metacatacryst, and later by Gotts dots, wedge, 26-cell quadratic growth, 25-cell quadratic growth, 24-cell quadratic growth, and switch-engine ping-pong.

The catacryst consists of three arks plus a glider-producing switch engine. It produces a block-laying switch engine every 47616 generations. Each block-laying switch engine has only a finite life, but the length of this life increases linearly with each new switch engine, so that the pattern overall grows quadratically, as an unusual type of MMS breeder.

:Catagolue An online database of objects in Conway's Game of Life and similar cellular automata, set up by Adam P. Goucher in 2015 at http://catagolue.appspot.com. It gathers data from a distributed search of random initial configurations and records the eventual decay products. Within a year of operation it had completed a census of the ash objects from over two trillion asymmetric 16×16 soups. As of August 2017 the number is near ten trillion.

It is often possible to find equivalent glider synthesis recipes for selected parts of long-running active reactions. Results from these random soup searches have made it possible to find efficient construction methods for thousands of increasingly rare still lifes and oscillators, and the occasional puffer or spaceship. In many of these cases a glider synthesis was previously very difficult or unknown.

:catalyst An object that participates in a reaction but emerges from it unharmed. The term is mostly applied to still lifes, but can also be used of oscillators, spaceships, etc. The still lifes and oscillators which form a conduit are examples of catalysts.

:caterer (p3) Found by Dean Hickerson, August 1989. Compare with jam. In terms of its minimum population of 12 this is the smallest p3 oscillator. See also double caterer and triple caterer.

	..O.....
	O...OOOO
	O...O...
	O.......
	...O....
	.OO.....
More generally, any oscillator which serves up a bit in the same manner may be referred to as a caterer.

:Caterloopillar A family of adjustable-speed spaceships constructed by Michael Simkin in 2016, based on idea originally proposed by David Bell. The front and back halves of Caterloopillars each function as universal constructors, with each half constructing the building blocks of the other half, while also reading and moving a construction tape. The overall design is reminiscent of M.C. Escher's lithograph "Drawing Hands". The name "Caterloopillar" is a reference to Douglas Hofstader's Strange Loop concept. Simkin has written an automated script that can construct a Caterloopillar for any rational speed strictly less than c/4 -- with some exceptions, mostly having to do with the size of the resulting spaceship. Lower speeds in general require larger constructions, and for any given computer system it is easy to choose a speed so slow that it is impractical to construct a Caterloopillar for it.. As of August 2017 one significant remaining limitation is that Caterloopillars with periods c/(6+4N) can't be constructed. However, this is only a limitation of the current construction script, not of the underlying Caterloopillar universal toolkit.

:Caterpillar A spaceship that works by laying tracks at its front end. The only example constructed to date is a p270 17c/45 spaceship built by Gabriel Nivasch in December 2004, based on work by himself, Jason Summers and David Bell. This Caterpillar has a population of about 12 million in each generation and was put together by a computer program that Nivasch wrote. At the time it was by far the largest and most complex Life object ever constructed, and it is still one of the largest in terms of population.

The 17c/45 Caterpillar is based on the following reaction between a pi-heptomino and a blinker:

	...............O
	O.............OO
	O............OO.
	O.............OO
	...............O
In this reaction, the pi moves forward 17 cells in the course of 45 generations, while the blinker moves back 6 cells and is rephased. This reaction has been known for many years, but it was only in September 2002 that David Bell suggested that it could be used to build a 17c/45 spaceship, based on a reaction he had found in which pis crawling along two rows of blinkers interact to emit a glider every 45 generations. Similar glider-emitting interactions were later found by Gabriel Nivasch and Jason Summers. The basic idea of the spaceship design is that streams of gliders created in this way can be used to construct fleets of standard spaceships which convey gliders to the front of the blinker tracks, where they can be used to build more blinkers.

A different Caterpillar may be possible based on the following reaction, in which the pattern at top left reappears after 31 generations displaced by (13,1), having produced a new NW-travelling glider. In this case the tracks would be waves of backward-moving gliders.

	.OO.....................
	...O....................
	...O.OO.................
	OOO....O................
	.......O................
	.....OOO................
	........................
	........................
	........................
	........................
	........................
	........................
	.....................OOO
	.....................O..
	......................O.
For other Caterpillar-type constructions see Centipede, waterbear, half-baked knightship, and Caterloopillar.

:CatForce An optimized search program written by Michael Simkin in 2015, using brute-force enumeration of small Spartan objects in a limited area, instead of a depth-first tree search. One major purpose of CatForce is to find glider-constructible completions for signal conduits. An early CatForce discovery was the B60 conduit, which enabled a record-breaking new glider gun.

:Catherine wheel = pinwheel

:cauldron (p8) Found in 1971 independently by Don Woods and Robert Wainwright. Compare with Hertz oscillator.

	.....O.....
	....O.O....
	.....O.....
	...........
	...OOOOO...
	O.O.....O.O
	OO.O...O.OO
	...O...O...
	...O...O...
	....OOO....
	...........
	....OO.O...
	....O.OO...

:cavity = eater plug

:cell The fundamental unit of space in the Life universe. The term is often used to mean a live cell - the sense is usually clear from the context.

:cellular automaton A certain class of mathematical objects of which Life is an example. A cellular automaton consists of a number of things. First there is a positive integer n which is the dimension of the cellular automaton. Then there is a finite set of states S, with at least two members. A state for the whole cellular automaton is obtained by assigning an element of S to each point of the n-dimensional lattice Zn (where Z is the set of all integers). The points of Zn are usually called cells. The cellular automaton also has the concept of a neighbourhood. The neighbourhood N of the origin is some finite (nonempty) subset of Zn. The neighbourhood of any other cell is obtained in the obvious way by translating that of the origin. Finally there is a transition rule, which is a function from SN to S (that is to say, for each possible state of the neighbourhood the transition rule specifies some cell state). The state of the cellular automaton evolves in discrete time, with the state of each cell at time t+1 being determined by the state of its neighbourhood at time t, in accordance with the transition rule.

There are some variations on the above definition. It is common to require that there be a quiescent state, that is, a state such that if the whole universe is in that state at generation 0 then it will remain so in generation 1. (In Life the OFF state is quiescent, but the ON state is not.) Other variations allow spaces other than Zn, neighbourhoods that vary over space and/or time, probabilistic or other non-deterministic transition rules, etc.

It is common for the neighbourhood of a cell to be the 3×...×3 (hyper)cube centred on that cell. (This includes those cases where the neighbourhood might more naturally be thought of as a proper subset of this cube.) This is known as the Moore neighbourhood.

:centinal (p100) Found by Bill Gosper. This combines the mechanisms of the p46 and p54 shuttles (see twin bees shuttle and p54 shuttle).

	OO................................................OO
	.O................................................O.
	.O.O.....................OO.....................O.O.
	..OO........O............OO............OO.......OO..
	...........OO..........................O.O..........
	..........OO.............................O..........
	...........OO..OO......................OOO..........
	....................................................
	....................................................
	....................................................
	...........OO..OO......................OOO..........
	..........OO.............................O..........
	...........OO..........................O.O..........
	..OO........O............OO............OO.......OO..
	.O.O.....................OO.....................O.O.
	.O................................................O.
	OO................................................OO

:Centipede (31c/240 orthogonally, p240) The smallest known 31c/240 spaceship, constructed by Chris Cain in September 2014 as a refinement of the shield bug.

:century (stabilizes at time 103) This is a common pattern which evolves into three blocks and a blinker. In June 1996 Dave Buckingham built a neat p246 glider gun using a century as the engine. See also bookend and diuresis.

	..OO
	OOO.
	.O..

:channel A lane or signal path, usually synchronized with one or more coordinated signals on other paths. See Gemini, Geminoid, construction arm, single-channel.

:chemist (p5)

	.......O.......
	.......OOO.....
	..........O....
	.....OOO..O..OO
	....O.O.O.O.O.O
	....O...O.O.O..
	.OO.O.....O.OO.
	..O.O.O...O....
	O.O.O.O.O.O....
	OO..O..OOO.....
	....O..........
	.....OOO.......
	.......O.......

:C-heptomino Name given by Conway to the following heptomino, a less common variant of the B-heptomino.

	.OOO
	OOO.
	.O..

:Cheshire cat A block predecessor by C. R. Tompkins that unaccountably appeared both in Scientific American and in Winning Ways. See also grin.

	.O..O.
	.OOOO.
	O....O
	O.OO.O
	O....O
	.OOOO.

:chicken wire A type of stable agar of density 1/2. The simplest version is formed from the tile:

	OO..
	..OO
But the "wires" can have length greater than two and need not all be the same. For example:
	OO...OOOO.....
	..OOO....OOOOO

:chirality A term borrowed from chemistry to describe asymmetrical patterns with two distinct mirror-image orientations. One common use is in relation to Herschel transmitters, where the spacing between the two gliders in the tandem glider output can limit the receiver to a single chirality.

:cigar = mango

:circuit Any combination of conduits or converters that moves or processes an active signal. This includes components with multiple states such as period multipliers or switches, which can be used to build guns, logic gates, universal constructors, and other computation or construction circuitry.

:cis-beacon on anvil (p2)

	...OO.
	....O.
	.O....
	.OO...
	......
	.OOOO.
	O....O
	.OOO.O
	...O.OO

:cis-beacon on table (p2)

	..OO
	...O
	O...
	OO..
	....
	OOOO
	O..O

:cis-boat with tail (p1)

	.O...
	O.O..
	OO.O.
	...O.
	...OO

:cis fuse with two tails (p1) See also pulsar quadrant.

	...O..
	.OOO..
	O...OO
	.O..O.
	..O.O.
	...O..

:cis-mirrored R-bee (p1)

	.OO.OO.
	O.O.O.O
	O.O.O.O
	.O...O.

:cis snake = canoe

:clean Opposite of dirty. A reaction which produces a small number of different products which are desired or which are easily deleted is said to be clean. For example, a puffer which produces just one object per period is clean. Clean reactions are useful because they can be used as building blocks in larger constructions.

When a fuse is said to be clean, or to burn cleanly, this usually means that no debris at all is left behind.

:clearance In signal circuitry, the distance from an edge shooter output lane to the last unobstructed lane adjacent to the edge-shooter circuitry. For example, an Fx119 inserter has an unusually high 27hd clearance.

:clock (p2) Found by Simon Norton, May 1970. This is the fifth or sixth most common oscillator, being about as frequent as the pentadecathlon, but much less frequent than the blinker, toad, beacon or pulsar. But it's surprisingly rare considering its small size.

	..O.
	O.O.
	.O.O
	.O..

:clock II (p4) Compare with pinwheel.

	......OO....
	......OO....
	............
	....OOOO....
	OO.O....O...
	OO.O..O.O...
	...O..O.O.OO
	...O.O..O.OO
	....OOOO....
	............
	....OO......
	....OO......

:clock inserter = clock insertion.

:clock insertion A uniquely effective method of adding a glider to the front edge of a salvo, by first constructing a clock, then converting it to a glider using a one-bit spark. Here it rebuilds a sabotaged eater in a deep pocket between other gliders:

	..................................................O........
	..................................................O.O......
	..................................................OO.......
	...............................................O......O....
	..............................................O......O.....
	..............................................OOO....OOO...
	...........................................................
	...........................................O......O........
	...........................................O.O....O.O.....O
	...........................................OO.....OO....OO.
	........................................O.......O........OO
	.......................................O...................
	.......................................OOO...........O.O...
	.....................................................OO....
	......................................................O....
	O..................................................O.......
	.OO..............................................OO........
	OO................................................OO.......
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	.............................O.............................
	....................O......O.O.............................
	..................O.O.......OO.............................
	...................OO......................................
	.........................O.................................
	..........................O....OOO.........................
	........................OOO....O...........................
	................................O..........................
	.....................................OO....................
	............................OO.......O.O...................
	............................O.O......O.....................
	............................O..............................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	.............................................OO............
	.............................................O.O...........
	.............................................O.............

In 2015 Chris Cain used this reaction to demonstrate conclusively that any unidirectional glider salvo, no matter how large or tightly packed, can be constructed by collisions between gliders that are initially separated by any finite distance. As a corollary, because all glider syntheses are made up of two to four unidirectional salvos, any glider-constructible object has a synthesis that starts with every glider at least N cells away from every other glider (for any chosen N).

:cloud of smoke = smoke

:cloverleaf This name was given by Robert Wainwright to his p2 oscillator washing machine. But Achim Flammenkamp also gave this name to Achim's p4.

:cluster Any pattern in which each live cell is connected to every other live cell by a path that does not pass through two consecutive dead cells. This sense is due to Nick Gotts, but the term has also been used in other senses, often imprecise.

:CNWH Conweh, creator of the Life universe.

:Coe ship (c/2 orthogonally, p16) A puffer engine discovered by Tim Coe in October 1995.

	....OOOOOO
	..OO.....O
	OO.O.....O
	....O...O.
	......O...
	......OO..
	.....OOOO.
	.....OO.OO
	.......OO.

In December 2015, the Coe ship was discovered in an asymmetric random soup on Catagolue. This was the first time any non-p4 ship was discovered in a random asymmetric soup experiment, winning Adam Goucher a 50-euro prize offered by Ivan Fomichev.

:Coe's p8 (p8) Found by Tim Coe in August 1997.

	OO..........
	OO..OO......
	.....OO.....
	....O..O....
	.......O..OO
	.....O.O..OO

:colour-changing See colour of a glider. The period-8 reflector shown in reflector is colour-changing, as are its p4/5/6/7 and higher-period versions.

:colourised Life A cellular automaton which is the same as Life except for the use of a number of different ON states ("colours"). All ON states behave the same for the purpose of applying the Life rule, but additional rules are used to specify the colour of the resulting ON cells. Examples are Immigration and QuadLife.

:colour of a glider The colour of a glider is a property of the glider which remains constant while the glider is moving along a straight path, but which can be changed when the glider bounces off a reflector. It is an important consideration when building something using reflectors.

The colour of a glider can be defined as follows. First choose some cell to be the origin. This cell is then considered to be white, and all other cells to be black or white in a checkerboard pattern. (So the cell with coordinates (m,n) is white if m+n is even, and black otherwise.) Then the colour of a glider is the colour of its leading cell when it is in a phase which can be rotated to look like this:

	OOO
	..O
	.O.

A reflector which does not change the colour of gliders obviously cannot be used to move a glider onto a path of different colour than it started on. But a 90-degree reflector which does change the colour of gliders is similarly limited, as the colour of the resulting glider will depend only on the direction of the glider, no matter how many reflectors are used. For maximum flexibility, therefore, both types of reflector are required.

:colour-preserving See colour of a glider. A Snark is a colour-preserving reflector.

:complementary blinker = fore and back

:component A partial glider synthesis that can be used in the same way in multiple glider recipes. A component transforms part of an object under construction in a well-defined way, without affecting the rest of the object. For example, this well-known component can be used to add a hook to any object that includes a protruding table end, converting it to a long bookend:

	.......O...................O...................O
	.....OO..................OO..................OO.
	......OO..................OO..................OO
	................................................
	..O...................O...................O.....
	O.O.................O.O.................O.O.....
	.OO..O...............OO..O...............OO..O..
	.....O.O.................O.O.................O.O
	.....OO..................OO..................OO.
	................................................
	................................................
	....................O...........................
	...O..O............O.O.O..O............OO..O..O.
	...OOOO.............OO.OOOO............O...OOOO.
	......................O.................OOO.....
	.....OO...............O.O.................O.O...
	.....OO................O.O.................OO...
	........................O.......................

:composite = composite conduit.

:composite conduit A signal-processing conduit that can be subdivided into two or more elementary conduits.

:compression = repeat time, recovery time.

:computational universality See universal computer.

:conduit Any arrangement of still lifes and/or oscillators which move an active object to another location, perhaps also transforming it into a different active object at the same time, but without leaving any permanent debris (except perhaps gliders, or other spaceships) and without any of the still lifes or oscillators being permanently damaged. Probably the most important conduit is the following remarkable one (Dave Buckingham, July 1996) in which a B-heptomino is transformed into a Herschel in 59 generations.

	.........OO.O
	O.OO......OOO
	OO.O.......O.
	.............
	.........OO..
	.........OO..
Several hundred elementary conduits are now known, with recent discoveries primarily made via search programs such as CatForce and Bellman.

:conduit 1 = BFx59H.

:confused eaters (p4) Found by Dave Buckingham before 1973.

	O..........
	OOO........
	...O.......
	..O........
	..O..O.....
	.....O.....
	...O.O.....
	...OO..OO..
	.......O.O.
	.........O.
	.........OO

:constellation A general term for a group of two or more separate objects, usually small still lifes and low-period oscillators. Compare pseudo still life.

:construction arm An adjustable mechanism in a universal constructor that allows new objects to be constructed in any chosen location that the arm can reach. A construction arm generally consists of a shoulder containing fixed guns or edge shooters, a movable construction elbow that slides forward and backward along the construction lane(s), and in the case of single-arm universal constructors, a hand target object at the construction site that can be progressively modified by a slow salvo to produce each desired object.

:construction elbow One of the components of a construction arm in a universal constructor. The elbow usually consists of a single Spartan still life or small constellation. It accepts elbow operation recipes, in the form of salvos coming from the construction arm's shoulder.

These recipes may do one of several things: 1) pull the elbow closer to the shoulder, 2) push the elbow farther from the shoulder, 3) emit a glider on a particular output lane (while also optionally pushing or pulling the elbow); 4) create a "hand" target block or other useful object as a target for output gliders, to one side of the construction lane; 5) duplicate the elbow, or 6) destroy the elbow.

Elbows that receive and emit orthogonally-traveling spaceships instead of gliders are technically possible, but no working examples are currently known. The discussion below assumes that gliders are used to communicate between the shoulder, elbow, and hand locations.

If a mechanism can be programmed to generate recipes for at least the first three options listed above, it is generally capable of functioning as a universal constructor. The main requirement is that push and pull elbow operations should be available that are either minimal (1fd) or the distances should be relatively prime.

Depending on the elbow operation library, there may be only one type of elbow, or there may be two or more elbow objects, with recipes that convert between them. The 9hd library had just one elbow type, a block. The original 10hd library had two elbows, blocks in mirror-symmetric locations; this was expanded to a larger list for the 10hd Demonoid. The 0hd Demonoid also has a multi-elbow recipe library. A slow elbow toolkit may make use of an even larger number of glider output recipes, because the target elbow object in that case is not restricted to a single diagonal line.

If only one colour, parity, or phase of glider can be emitted, then the mechanism will be limited to producing monochromatic salvos or monoparity salvos. These are less efficient at most construction tasks, but are still generally accepted to enable universal toolkits. See also half-baked knightship.

:construction envelope The region affected by an active reaction, such as a glider construction of an object. The envelope corresponds to the state-2 blue cells in LifeHistory. See also edgy.

:construction lane Part of a construction arm between the shoulder and the elbow -- in particular, one of the fixed lanes that elbow operation signals travel on. All known universal constructors have used arms with two or more construction lanes, except for the 0hd Demonoid and single-lane construction recipes.

:construction recipe One or more streams of gliders or other signals fed into a universal constructor to create a target object. Compare glider recipe.

:construction universality See universal constructor.

:converter A conduit in which the input object is not of the same type as the output object. This term tends to be preferred when either the input object or the output object is a spaceship.

The following diagram shows a p8 pi-heptomino-to-HWSS converter. This was originally found by Dave Buckingham in a larger form (using a figure-8 instead of the boat). The improvement shown here is by Bill Gosper (August 1996). Dieter Leithner has since found (much larger) oscillators of periods 44, 46 and 60 that can be used instead of the Kok's galaxy.

	.O.O..O........
	.OOO.O.OO......
	O......O.....O.
	.O.....OO...O.O
	.............OO
	OO.....O.......
	.O......O......
	OO.O.OOO.......
	..O..O.O.......
	............OOO
	............O.O
	............O.O

Other elementary conduit converters include BFx59H, 135-degree MWSS-to-G, and 45-degree MWSS-to-G.

:convoy A collection of spaceships all moving in the same direction at the same speed.

:copperhead (c/10 orthogonally, p10) The following small c/10 spaceship, discovered by conwaylife.com forum user 'zdc' on 5 March 2016, using a simple depth-first search program. A glider synthesis was found on the same day.

	.OOOO.
	......
	.O..O.
	O.OO.O
	O....O
	......
	O....O
	OO..OO
	OOOOOO
	.O..O.
	..OO..
	..OO..
Later that same month Simon Ekstrom added a sparky tagalong for the copperhead to produce the fireship. This allowed for the construction of c/10 puffers and rakes.

:Corder- Prefix used for things involving switch engines, after Charles Corderman.

:Corder engine = switch engine

:Cordergun A gun firing Corderships. The first was built by Jason Summers in July 1999, using a glider synthesis by Stephen Silver.

:Cordership Any spaceship based on switch engines. These necessarily move at a speed of c/12 diagonally with a period of 96 (or a multiple thereof). The first was found by Dean Hickerson in April 1991. Corderships are the slowest spaceships so far constructed, although arbitrarily slow spaceships are known to exist (see universal constructor). Hickerson's original Cordership used 13 switch engines. He soon reduced this to 10, and in August 1993 to 7. In July 1998 he reduced it to 6. In January 2004, Paul Tooke found the 3-engine Cordership shown below.

	................................OO.O...........................
	...............................OOO.O......O.O..................
	..............................O....O.O....O....................
	...............................OO......O.O...O.................
	................................O...O..O..OO...................
	...................................O.OO...O....................
	..................................O.O................OO........
	..................................O.O................OO........
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	...............................................................
	.............................................................OO
	....................................................OO.......OO
	.......................................O.........O.OOOO........
	..................................O...OOOOO.....OO.O...OO......
	.................................O.O.......OO....O..OO.OO......
	.................................O.......O.OO.....OOOOOO.......
	..................................O........OO......O...........
	...................................O...OOOO....................
	........................................OOO....................
	........................O.O.........OO.........................
	........................O.O.O......O.O.........................
	.......................O..OO.O....OO...........................
	........................OO...O.O.OO.O..........................
	........................OO...OO.OOOOO..........................
	............................O.OO...OO..........................
	...........................O.O.................................
	..OO.O.........................................................
	.OOO.O......O.O................................................
	O....O.O....O..................................................
	.OO......O.O...O...............................................
	..O...O..O..OO...........O.....................................
	.....O.OO...O...........OOO....................................
	....O.O.................O..O...................................
	....O.O................O....O..................................
	........................O......................................
	...............................................................
	........................O..O...................................
	.........................O.O...................................
	...............................................................
	.....................O.........................................
	....................OOO........................................
	...................OO.OO.......................................
	.........O........OO.O.....O...................................
	....O...OOOOO....OO......OO....................................
	...O.O.......OO..OO.......OO...................................
	...O.......O.OO................................................
	....O........OO................................................
	.....O...OOOO..................................................
	..........OOO..................................................
	...............................................................
	...............................................................
	...............................................................
	...........OO..................................................
	...........OO..................................................

:cousins (p3) This contains two copies of the stillater rotor.

	.....O.OO....
	...OOO.O.O...
	O.O......O...
	OO.OO.OO.O.OO
	...O.O....O.O
	...O.O.OOO...
	....OO.O.....

:cover The following induction coil. See scrubber for an example of its use.

	....O
	..OOO
	.O...
	.O...
	OO...

:covered table = cap

:cow (c p8 fuse)

	OO.......OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO.....
	OO....O.OOO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO...OO
	....OO.O.................................................O.O
	....OO...OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO..
	....OO.O..................................................O.
	OO....O.OOO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO.
	OO.......OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO.....

:CP pulsar = pulsar

:crab = quarter.

:crane (c/4 diagonally, p4) The following spaceship found by Nicolay Beluchenko in September 2005, a minor modification of a tubeater found earlier by Hartmut Holzwart. The wing is of the same form as in the swan and Canada goose.

	.OO.................
	OO..................
	..O.................
	....OO...O..........
	....OO..O.O.........
	.......OO.O.........
	.......OO...........
	.......OO...........
	.................OO.
	.........O....OO.O..
	.........OOO..OO....
	.........OOO..OO....
	..........OO........
	....................
	............O.......
	...........OO.......
	...........O........
	............O.......
	....................
	.............OO.....
	..............O.OO..
	..................O.
	...............OO...
	...............OO...
	.................O..
	..................OO

:cross (p3) Found by Robert Wainwright in October 1989.

	..OOOO..
	..O..O..
	OOO..OOO
	O......O
	O......O
	OOO..OOO
	..O..O..
	..OOOO..
In February 1993, Hartmut Holzwart noticed that this is merely the smallest of an infinite family of p3 oscillators. The next smallest member is shown below.
	..OOOO.OOOO..
	..O..O.O..O..
	OOO..OOO..OOO
	O...........O
	O...........O
	OOO.......OOO
	..O.......O..
	OOO.......OOO
	O...........O
	O...........O
	OOO..OOO..OOO
	..O..O.O..O..
	..OOOO.OOOO..

:crowd (p3) Found by Dave Buckingham in January 1973.

	...........O..
	.........OOO..
	.....OO.O.....
	.....O...O....
	.......OO.O...
	...OOOO...O...
	O.O.....O.O.OO
	OO.O.O.....O.O
	...O...OOOO...
	...O.OO.......
	....O...O.....
	.....O.OO.....
	..OOO.........
	..O...........

:crown The p12 part of the following p12 oscillator, where it is hassled by caterer, a jam and a HW emulator. This oscillator was found by Noam Elkies in January 1995.

	..........O...........
	..........O......O....
	...O....O...O...OO....
	...OO....OOO..........
	.........OOO..OOO..O.O
	.O..OOO.........O.OOOO
	O.O.O...............OO
	O..O..................
	.OO........OO.........
	......OO.O....O.OO....
	......O..........O....
	.......OO......OO.....
	....OOO..OOOOOO..OOO..
	....O..O........O..O..
	.....OO..........OO...

:crucible = cauldron

:crystal A regular growth that is sometimes formed when a stream of gliders, or other spaceships, is fired into some junk.

The most common example is initiated by the following collision of a glider with a block. With a glider stream of even period at least 82, this gives a crystal which forms a pair beehives for every 11 gliders which hit it.

	.O......
	..O...OO
	OOO...OO

:crystal and decay See also crystal.

.....OO.......................................................................
.....OO.......................................................................
..............................................................................
..............................................................................
.....O........................................................................
....OOO.......................................................................
...O...O......................................................................
.....O..................OO....................................................
..O.....O...............O.O...................................................
..O.....O................OOO............O.....................................
...O...O.......OO.........OOO........OOOO.....................................
....OOO........OO........OOO........OOOO......................................
........................O.O.........O..O.........OO...........................
........................OO..........OOOO.........OO...........................
.....................................OOOO.....................................
........................................O.....................................
..............................................................................
..............................................................................
..............................................................................
.......O......................................................................
.....O.O......................................................................
......OO......................................................................
..............................................................................
..............................................................................
..............................................................................
OO...OO.......................................................................
..............................................................................
.O...O........................................................................
..OOO.........................................................................
..OOO.........................................................................
..............................................................................
..............................................................................
...................................O..........................................
.................................OOO..........................................
...OO...........................O.............................................
...OO...........................OO............................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
....................OO........................................................
....................O.........................................................
.....................OOO......................................................
.......................O......................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..................................................................OO......OO..
.................................................................O..O....O..O.
................................................................OOOOOO..OOOOOO
.................................................................O..O....O..O.
..................................................................OO......OO..
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..............................................................................
...........................................................OOO................
...........................................................O.O................
...........................................................OOO................
...........................................................OOO................
...........................................................OOO................
...........................................................OOO................
...........................................................O.O................
...........................................................OOO................

:cuphook (p3) Found by Rich Schroeppel, October 1970. This is one of only three essentially different p3 oscillators with only three cells in the rotor. The others are 1-2-3 and stillater.

	....OO...
	OO.O.O...
	OO.O.....
	...O.....
	...O..O..
	....OO.O.
	.......O.
	.......OO
The above is the original form, but it can be made more compact:
	....OO.
	...O.O.
	...O...
	OO.O...
	OO.O..O
	...O.OO
	...O...
	..OO...

:curl = loop

:dart (c/3 orthogonally, p3) Found by David Bell, May 1992. A 25-glider recipe for the dart was found in December 2014 by Martin Grant and Chris Cain, making it the first glider-constructible c/3 spaceship.

	.......O.......
	......O.O......
	.....O...O.....
	......OOO......
	...............
	....OO...OO....
	..O...O.O...O..
	.OO...O.O...OO.
	O.....O.O.....O
	.O.OO.O.O.OO.O.

:dead spark coil (p1) Compare spark coil.

	OO...OO
	O.O.O.O
	..O.O..
	O.O.O.O
	OO...OO

:debris = ash.

:de Bruijn diagram = de Bruijn graph

:de Bruijn graph As applied to Life, a de Bruijn graph is a graph showing which pieces can be linked to which other pieces to form a valid part of a Life pattern of a particular kind.

For example, if we are interested in still lifes, then we could consider 2×3 rectangular pieces and the de Bruijn graph would show which pairs of these can be overlapped to form 3×3 squares in which the centre cell remains unchanged in the next generation.

David Eppstein's search program gfind is based on de Bruijn graphs.

:Deep Cell A pattern by Jared James Prince, based on David Bell's unit Life cell, in which each unit cell simulates two Life cells, in such a way that a Life universe filled with Deep Cells simulates two independent Life universes running in parallel.

In fact, a Life universe filled with Deep Cells can simulate infinitely many Life universes, as follows. Let P1, P2, P3, ... be a sequence of Life patterns. Set the Deep Cells to run a simulation of P1 in parallel with a simulation of a universe filled with Deep Cells, with these simulated Deep Cells running a simulation of P2 in parallel with another simulation of a universe filled with Deep Cells, with these doubly simulated Deep Cells simulating P3 in parallel with yet another universe of Deep Cells, and so on.

Deep Cell is available from http://psychoticdeath.com/life.htm.

:Demonoid The first self-constructing diagonal spaceship. A 0hd Demonoid was completed by Chris Cain in December 2015, shortly after a much larger 10hd version constructed the previous month in collaboration with Dave Greene. The 0hd spaceship fits in a bounding box about 55,000 cells square, and displaces itself by 65 cells diagonally every 438,852 generations.

The first 0hd Demonoid was fired by a gun. As of this writing (2017) this is the only case where a spaceship gun pattern was completed before the first appearance of the actual spaceship.

:density The density of a pattern is the limit of the proportion of live cells in a (2n+1)×(2n+1) square centred on a particular cell as n tends to infinity, when this limit exists. (Note that it does not make any difference what cell is chosen as the centre cell. Also note that if the pattern is finite then the density is zero.) There are other definitions of density, but this one will do here.

In 1994 Noam Elkies proved that the maximum density of a stable pattern is 1/2, which had been the conjectured value. See the paper listed in the bibliography. Marcus Moore provided a simpler proof in 1995, and in fact proves that a still life with an m × n bounding box has at most (mn+m+n)/2 cells.

But what is the maximum average density of an oscillating pattern? The answer is conjectured to be 1/2 again, but this remains unproved. The best upper bound so far obtained is 8/13 (Hartmut Holzwart, September 1992).

The maximum possible density for a phase of an oscillating pattern is also unknown. An example with a density of 3/4 is known (see agar), but densities arbitrarily close to 1 may perhaps be possible.

:dependent conduit A Herschel conduit in which the input Herschel interacts with catalysts in the first few ticks -- technically at T=-3, before the Herschel is completely formed. Compare independent conduit. The Herschel is prevented from emitting its first natural glider, This is useful in cases where the previous conduit cannot survive a first natural glider emitted from its output Herschel.

This term is somewhat confusing, since it is actually the previous conduit that depends on the dependent conduit to suppress the problematic glider. Dependent conduits such as the F166 and Lx200 do not actually depend on anything. They can be freely connected to any other conduits that fit, as long as the output Herschel evolves from its standard great-grandparent. As of this writing, the Fx158 is the only known case where a conduit?output Herschel has an alternate great-grandparent, which is incompatible with dependent conduits' initial transparent block.

:destructor arm A dedicated construction arm in the Gemini spaceship, used only for removing previously active circuitry once it is no longer needed. More generally, any circuitry in a self-constructing pattern dedicated exclusively to cleanup.

:D-heptomino = Herschel

:diamond = tub

:diamond ring (p3) Found by Dave Buckingham in 1972.

	......O......
	.....O.O.....
	....O.O.O....
	....O...O....
	..OO..O..OO..
	.O....O....O.
	O.O.OO.OO.O.O
	.O....O....O.
	..OO..O..OO..
	....O...O....
	....O.O.O....
	.....O.O.....
	......O......

:diehard Any pattern that vanishes, but only after a long time. The following example vanishes in 130 generations, which is probably the limit for patterns of 7 or fewer cells. Note that there is no limit for higher numbers of cells - e.g., for 8 cells we could have a glider heading towards an arbitrarily distant blinker.

	......O.
	OO......
	.O...OOO

:dinner table (p12) Found by Robert Wainwright in 1972.

	.O...........
	.OOO.......OO
	....O......O.
	...OO....O.O.
	.........OO..
	.............
	.....OOO.....
	.....OOO.....
	..OO.........
	.O.O....OO...
	.O......O....
	OO.......OOO.
	...........O.

:dirty Opposite of clean. A reaction which produces a large amount of complicated junk which is difficult to control or use is said to be dirty. Many basic puffer engines are dirty and need to be tamed by accompanying spaceships in order to produce clean output. Similarly, a dirty conduit is one that does not recover perfectly after the passage of a signal; one or more extra ash objects are left behind (or more rarely a catalyst is damaged) and additional signals must be used to clean up the circuit before it can be re-used.

:diuresis (p90) Found by David Eppstein in October 1998. His original stabilization used pentadecathlons. The stabilization with complicated still lifes shown here (in two slightly different forms) was found by Dean Hickerson the following day. The name is due to Bill Gosper (see kidney).

	.....OO................OO....
	......O................O.....
	......O.O............O.O.....
	.......OO............OO......
	.............................
	....OO..................OO...
	....O.O..........OO....O.O...
	.....O..........O.O.....O....
	..O.............OO.........O.
	..OOOOOO........O.....OOOOOO.
	.......O..............O......
	....OO..................OO...
	....O....................O...
	.....O..................O....
	..OOO..O..............O..OOO.
	..O..OOO........O.....OOO...O
	...O............OO.......OOO.
	....OO..........O.O.....O....
	......O..........OO....O..OO.
	....OO..................OO.O.
	.O..O....................O...
	O.O.O..OO............OO..O...
	.O..O.O.O............O.O.OO..
	....O.O................O..O..
	.....OO................OO....

:dock The following induction coil.

	.OOOO.
	O....O
	OO..OO

:domino The 2-cell polyomino. A number of objects, such as the HWSS and pentadecathlon, produce domino sparks.

:do-see-do The following reaction, found by David Bell in 1996, in which two gliders appear to circle around each other as they are reflected 90 degrees by a twin bees shuttle. Four copies of the reaction can be used to create a p92 glider loop which repeats the do-see-do reaction forever.

	.....................................................O.O
	.....................................................OO.
	......................................................O.
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	........................................................
	................................................OO......
	................................................O.......
	..............................................O.O.......
	..............................................OO........
	..............................O.O.......................
	..............................OO........................
	...............................O........................
	........................................................
	.......................OOO..............................
	OO........OOO........OO.O.OO............................
	OO........O...O.....O.....OO............................
	..........O....O.....OO.O.OO............................
	...........O...O.......OOO..............................
	........................................................
	...........O...O........................................
	..........O....O........................................
	OO........O...O............OO...........................
	OO........OOO..............OO...........................

:double-barrelled Of a gun, emitting two streams of spaceships (or rakes). See B-52 bomber for an example.

:double block reaction A certain reaction that can be used to stabilize the twin bees shuttle (qv). This was discovered by David Bell in October 1996.

The same reaction sometimes works in other situations, as shown in the following diagram where a pair of blocks eats an R-pentomino and a LWSS. (The LWSS version was known at least as early 1994, when Paul Callahan saw it form spontaneously as a result of firing a LWSS stream at some random junk.)

	.OOOO.....OO....
	O...O......OO.OO
	....O......O..OO
	O..O............
	................
	.............OO.
	.............OO.

:double caterer (p3) Found by Dean Hickerson, October 1989. Compare caterer and triple caterer.

	.....OO...O........
	....O..O..OOO......
	....OO.O.....O.....
	......O.OOOO.O.....
	..OOO.O.O...O.OO...
	.O..O..O...O..O.O..
	O.O..O...O.OO....O.
	.O..........OO.OOO.
	..OO.OO.OO...O.....
	...O...O.....O.OOO.
	...O...O......OO..O
	.................OO

:double ewe (p3) Found by Robert Wainwright before September 1971.

	......OO............
	.......O............
	......O.............
	......OO............
	.........OO.........
	......OOO.O.........
	O.OO.O..............
	OO.O.O..............
	.....O...O..........
	....O...OO....OO....
	....OO....OO...O....
	..........O...O.....
	..............O.O.OO
	..............O.OO.O
	.........O.OOO......
	.........OO.........
	............OO......
	.............O......
	............O.......
	............OO......

:double wing = moose antlers. This term is no longer in use.

:dove The following induction coil, found in 2015 to be a possible active reaction for the input or output of a converter.

	.OO..
	O..O.
	.O..O
	..OOO

:down boat with tail = cis-boat with tail

:dr Short identifier for Dean Hickerson's 'drifter' search program, used at various times to find wires, eaters, higher-period billiard table configurations, and related signal-carrying and signal-processing mechanisms. See also drifter.

:dragon (c/6 orthogonally, p6) This spaceship, discovered by Paul Tooke in April 2000, was the first known c/6 spaceship. With 102 cells, it was the smallest known orthogonal c/6 spaceship until Hartmut Holzwart discovered 56P6H1V0 in April 2009.

	.............O..OO......O..OOO
	.....O...OOOO.OOOOOO....O..OOO
	.OOOOO....O....O....OOO.......
	O......OO.O......OO.OOO..O.OOO
	.OOOOO.OOO........OOOO...O.OOO
	.....O..O..............O......
	........OO..........OO.OO.....
	........OO..........OO.OO.....
	.....O..O..............O......
	.OOOOO.OOO........OOOO...O.OOO
	O......OO.O......OO.OOO..O.OOO
	.OOOOO....O....O....OOO.......
	.....O...OOOO.OOOOOO....O..OOO
	.............O..OO......O..OOO

:drain trap = paperclip. This term is no longer in use.

:dried = freeze-dried.

:drifter A perturbation moving within a stable pattern. Dean Hickerson has written a program to search for drifters, with the hope of finding one which could be moved around a track. Because drifters can be very small, they could be packed more tightly than Herschels, and so allow the creation of oscillators of periods not yet attained, and possibly prove that Life is omniperiodic. Hickerson has found a number of components towards this end, but it has proved difficult to change the direction of movement of a drifter, and so far no complete track has been found. However, Hickerson has had success using the same search program to find eaters with novel properties, such as that used in diuresis.

:dual 1-2-3-4 = Achim's p4

:duoplet A diagonal two-bit spark produced by many oscillators and eater reactions. Among other uses, it can reflect gliders 90 degrees. The following pattern shows an eater5 eating gliders and producing duoplets which are then used to reflect a separate glider stream.

	..O....................
	O.O....................
	.OO....................
	.......................
	.......................
	.......O...............
	.....O.O...............
	......OO...............
	.....................O.
	....................O..
	....................OOO
	.......................
	.......................
	................O......
	...............O.......
	...............OOO.....
	.......................
	....................OO.
	................O...OO.
	...............O.O.....
	..............O.O......
	..............O........
	.............OO........

:dying spark See spark. A spark by definition dies out completely after some number of ticks.

:early universe Conway's somewhat confusing term for sparse Life.

:eater Any still life that has the ability to interact with certain patterns without suffering any permanent damage. (If it doesn't suffer even temporary damage then it may be referred to as a rock.) The eater1 is a very common eater, and the term "eater" is often used specifically for this object. Other eaters include eater2, eater3, eater4 and even the humble block. (In fact the block was the first known eater, being found capable of eating beehives from a queen bee.) Another useful eater is shown below, feasting on a glider.

	...O.....
	...O.O...
	...OO....
	.........
	.......OO
	...O...OO
	..O.O....
	.O.O.....
	.O.......
	OO.......

:eater1 (p1) Usually simply called an eater, and also called a fishhook. Its ability to eat various objects was discovered by Bill Gosper in 1971.

	OO..
	O.O.
	..O.
	..OO

:eater2 (p1) This eater was found by Dave Buckingham in the 1970s. Mostly it works like the ordinary eater (see eater1) but with two slight differences that make it useful despite its size: it takes longer to recover from each bite, and it can eat objects appearing at two different positions.

	...O.OO
	.OOO.OO
	O......
	.OOO.OO
	...O.O.
	...O.O.
	....O..
The first property means that, among other things, it can eat a glider in a position that would destroy a fishhook. This novel glider-eating action is occasionally of use in itself, and combined with the symmetry means that an eater2 can eat gliders traveling along four adjacent glider lanes, as shown below.

The following eater2 variant (Stephen Silver, May 1998) can be useful for obtaining smaller bounding boxes. A more compact variant with the same purpose can be seen under gliderless.

	.O.................
	..O................
	OOO................
	...................
	....O..............
	.....O.............
	...OOO.............
	...................
	.......O...........
	........O..........
	......OOO..........
	...................
	..........O........
	...........O.....OO
	.........OOO......O
	.............OO.O..
	.............OO.OO.
	...................
	.............OO.OO.
	..............O.O..
	..............O.O..
	...............O...

:eater3 (p1) This large symmetric eater, found by Dave Buckingham, has a very different eating action from the eater1 and eater2. The loaf can take bites out things, being flipped over in the process. The rest of the object merely flips it back again.

	.........OO.
	....OO..O..O
	.O..O....O.O
	O.O.O.....O.
	.O..O.OO....
	....O..O....
	.....O....O.
	......OOOOO.
	............
	........O...
	.......O.O..
	........O...

:eater4 (p1) Another eater by Dave Buckingham, which he found in 1971, but did not recognize as an eater until 1975 or 1976. It can't eat gliders, but it can be used for various other purposes. The four NE-most centre cells regrow in a few generations after being destroyed by taking a bite out of something.

	...OO.........
	...O..........
	OO.O..........
	O..OO.........
	.OO....O......
	...OOOOO......
	...O....OO....
	....OO..O.....
	......O.O.....
	......O.O.O..O
	.......OO.OOOO
	.........O....
	.........O.O..
	..........OO..

:eater5 (p1) A compound eater that can eat gliders coming from two different directions. Also called the tub-with-tail eater (TWIT), it is often placed along the edges of glider lanes to suppress unwanted gliders in conduits. Below is the standard form, a compact form with a long hook, and an often-useful conjoined form found with Bellman. The sidesnagger is a Spartan constellation that has a similar glider-absorbing function, using a loaf. See also 7x9 eater.

	.O.........O.........O...........
	..O.........O.........O..........
	OOO.......OOO.......OOO..........
	.................................
	......O.........O.........O......
	.....O.........O.........O.......
	.....OOO.......OOO.......OOO.....
	.................................
	..........OO.....................
	......O...OO....O...OO....O...OO.
	.....O.O.......O.O...O...O.O...O.
	....O.O.......O.O...O....OO...O..
	....O.........O....O.........O...
	...OO........OO.....OOO..OOOOO.O.
	......................O..O....O.O
	...........................O..O.O
	..........................OO...O.

:eater/block frob (p4) Found by Dave Buckingham in 1976 or earlier.

	.OO.......
	..O.......
	..O.O.....
	...O.O....
	.....OO.OO
	........OO
	..OO......
	...O......
	OOO.......
	O.........

:eater-bound pond = biting off more than they can chew

:eater-bound Z-hexomino = pentoad

:eater eating eater = two eaters

:eater plug (p2) Found by Robert Wainwright, February 1973.

	.......O
	.....OOO
	....O...
	.....O..
	..O..O..
	.O.OO...
	.O......
	OO......

:eaters plus = French kiss

:ecologist (c/2 orthogonally, p20) This consists of the classic puffer train with a LWSS added to suppress the debris. See also space rake.

	OOOO.....OO........
	O...O...OO.OO......
	O........OOOO......
	.O..O.....OO.......
	...................
	.....O.........OO..
	...OOO........OOOOO
	..O...O.....O....OO
	..O....OOOOO.....OO
	..OO.O.OOOO....OO..
	....O...OO.OOO.....
	.....O.O...........
	...................
	...................
	OOOO...............
	O...O..............
	O..................
	.O..O..............

:edge-repair spaceship A spaceship which has an edge that possesses no spark and yet is able to perturb things because of its ability to repair certain types of damage to itself. The most useful examples are the following two small p3 c/3 spaceships:

	..................................O.....
	........O.......................OOO.OOO.
	.......OOOO....................OO......O
	..O...O...OO.OO...........O...O..O...OO.
	.OOOO.....O..OO..........OOOO...........
	O...O.......O..O........O...O...........
	.O.O..O..................O.O..O.........
	.....O.......................O..........
These were found by David Bell in 1992, but the usefulness of the edge-repair property wasn't recognised until July 1997. The following diagram (showing an edge-repair spaceship deleting a Herschel) demonstrates the self-repairing action.
	................O.......
	O..............OOOO.....
	O.O.......O...O...OO.OO.
	OOO......OOOO.....O..OO.
	..O.....O...O.......O..O
	.........O.O..O.........
	.............O..........
In October 2000, David Bell found that a T-tetromino component of a c/4 spaceship can also be self-repairing. Stephen Silver noticed that it could be used to delete beehives and, in November 2000, found the smallest known c/4 spaceship with this edge-repair component - in fact, two copies of the component:
	.OO..........................
	O..O.........................
	.OO..........................
	.............................
	.......O.O...................
	.......O.....................
	.......O.O..O..O.............
	..........O..................
	...........O.OO.O............
	............OOO.O............
	...........O....O..O.OO......
	........O...OO...O.OOOO......
	........OO..O..O.OO....O....O
	........O........OO....O..OOO
	.............OO...OO...O..OO.
	.OO..........................
	O..O.........................
	.OO..........................

:edge shooter A gun which fires its gliders (or whatever) right at the edge of the pattern, so that it can be used to fire them closely parallel to others. This is useful for constructing complex guns. Compare glider pusher, which can in fact be used for making edge shooters.

The following diagram shows a p46 edge shooter found by Paul Callahan in June 1994.

	OO............OO..O....OO..OO.............
	OO............O.OO......OO.OO.............
	...............O......O.O.................
	...............OOO....OO..................
	..........................................
	...............OOO....OO..................
	...............O......O.O.................
	OO............O.OO......OO................
	OO............OO..O....OO.................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	...............................OOO...OOO..
	..............................O...O.O...O.
	.............................O...OO.OO...O
	.............................O.OO.....OO.O
	...............................O.......O..
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	..........................................
	...............................OO.....OO..
	...............................OO.....OO..

:edge spark A spark at the side of a spaceship that can be used to perturb things as the spaceship passes by.

:edge sparker A spaceship that produces one or more edge sparks.

:edgy In slow salvo terminology, an edgy glider construction recipe is one that places its final product at or very near the edge of its construction envelope.

:egg = non-spark. This term is no longer in use.

:E-heptomino Name given by Conway to the following heptomino.

	.OOO
	OO..
	.OO.

:elbow Depending on context, this term may refer to a signal elbow or a construction elbow. See also elbow ladder.

:elbow ladder Scot Ellison's name for the type of pattern he created in which one or more gliders shuttle back and forth (using the kickback reaction) deleting the output gliders from a pair of slide guns.

:elbow operation A recipe, usually a salvo of gliders traveling on one or more construction lanes, that collides with an elbow constellation and performs one of the standard transformations on it -- push, pull, or fire for simple construction arms, along with possible construct, duplicate-elbow, or delete-elbow ops for more complicated systems. See construction elbow.

:electric fence (p5) A stabilization of ants. Dean Hickerson, February 1993.

	..........O..................................................
	.........O.O........................OO.......................
	..O....OOO.O.....O...................O...O..O......O.....OO..
	.O.O..O....OO...O.O..................O.OOO..OOO...O.O....O...
	.O.O..O.OO.......O....................O...OO...O.O..O......O.
	OO.OO.O.O.OOOOO.....O..................OO...O..O.O.OO.OO..OO.
	.O.O..O...O..O..O.......OO...OO...OO....OO.OO..O.O..O.O.O....
	.O..OO....OO......OOO.OO...OO...OO...OOO.....OOOO.OOO.O...OO.
	..O..OOO..O..O.OOOO...OO...OO...OO...OOO.OO..O....O.O....O..O
	...OO...O.O..O.....OO...OO...OO...OO......O............O...OO
	.....OO.O.OO.O.OO..O......................O........OO.O......
	.....O.OO.O..O.OO....O.................OO.O.O................
	...........OO.......OO..................O..OO................
	......................................O.O....................
	......................................OO.....................

:Electric X Star Constructed by Otis Arron Schmakel in December 2004, from various Oscillators.

..............................................................................................O.......O..............................................................................................
.............................................................................................O.O.....O.O.............................................................................................
.............................................................................................O.O.....O.O.............................................................................................
...........................................................................................OOO.OO...OO.OOO...........................................................................................
..........................................................................................O...............O..........................................................................................
...........................................................................................OOOO.....OO.OOO...........................................................................................
.............................................................................................O.OO...OO.O.............................................................................................
.....................................................................................................................................................................................................
..................................................................................................OO.................................................................................................
..................................................................................................O..................................................................................................
..................................................................................................O..................................................................................................
.................................................................................................OO..................................................................................................
.....................................................................................................................................................................................................
.............................................................................................O.OO...OO.O.............................................................................................
...........................................................................................OOO.OO.....OOOO...........................................................................................
..........................................................................................O...............O..........................................................................................
...........................................................................................OOO.OO...OO.OOO...........................................................................................
.............................................................................................O.O.....O.O.............................................................................................
.............................................................................................O.O.....O.O.............................................................................................
..............................................................................................O.......O..............................................................................................
.....................................................................................................................................................................................................
.....................................................................................................................................................................................................
....................................................................................OOO.O..O.O.........O.O..O.OOO....................................................................................
.....................................................................................O.O.O.O..O.......O..O.O.O.O.....................................................................................
..............................................................................................O.......O..............................................................................................
.......................................................................................O.....................O.......................................................................................
.......................................................................................O..O.O.O.O...O.O.O.O..O.......................................................................................
........................................................................................O.O..O.OOO.OOO.O..O.O........................................................................................
.....................................................................................................................................................................................................
.....................................................................................................................................................................................................
.....................................................................................................................................................................................................
...........................................................................O...................OOO.OOO...................O...........................................................................
...........................................................................OO...................O...O...................OO...........................................................................
...........................................................................O....................O...O....................O...........................................................................
............................................................................O.OO.....................................OO.O............................................................................
...........................................................................O....O..............OOO.OOO..............O....O...........................................................................
............................................................................O...........................................O............................................................................
...............................................................................OO...................................OO...............................................................................
...........................................................................OO...........................................OO...........................................................................
...........................................O......O............................O..............OO.....OO..............O............................O......O...........................................
..........................................O.OO..OO.O.......................O....O................O.O................O....O.......................O.OO..OO.O..........................................
..........................................O.OO..OO.O........................OO.O............O..O.O.O.O..O............O.OO........................O.OO..OO.O..........................................
........................................OO.OOO..OOO.OO..........................O...O...O...O.O..O.O..O.O...O...O...O..........................OO.OOO..OOO.OO........................................
.......................................O..O........O..O........................OO...OOO.O........O.O........O.OOO...OO........................O..O........O..O.......................................
........................................OOO........OOO..........................O...O...O....OOOO...OOOO....O...O...O..........................OOO........OOO........................................
........................................OOO........OOO.........................................................................................OOO........OOO........................................
..............................................OO................................O...O...O....OOOO...OOOO....O...O...O................................OO..............................................
..............................................OO..........OOO..................OO...OOO.O........O.O........O.OOO...OO..................OOO..........OO..............................................
........................................OOO........OOO..........................O...O...O...O.O..O.O..O.O...O...O...O..........................OOO........OOO........................................
........................................OOO........OOO...O...O..............OO.O............O..O.O.O.O..O............O.OO..............O...O...OOO........OOO........................................
.......................................O..O........O..O...O.O..............O....O................O.O................O....O..............O.O...O..O........O..O.......................................
........................................OO.OOO..OOO.OO.....O...................O..............OO.....OO..............O...................O.....OO.OOO..OOO.OO........................................
..........................................O.OO..OO.O.....O...O.............OO...........................................OO.............O...O.....O.OO..OO.O..........................................
..........................................O.OO..OO.O...O.OO.OO.O...............OO...................................OO...............O.OO.OO.O...O.OO..OO.O..........................................
...........................................O......O....O..O.O..O............O...........................................O............O..O.O..O....O......O...........................................
.....................................................OO..OO.OO..OO.........O....O..............OOO.OOO..............O....O.........OO..OO.OO..OO.....................................................
..........................................................O.O...............O.OO.....................................OO.O...............O.O..........................................................
.................................................O..OO.O..O.O..O.OO..O.....O....................O...O....................O.....O..OO.O..O.O..O.OO..O.................................................
...............................................O..O..OOOOO...OOOOO..O..O...OO...................O...O...................OO...O..O..OOOOO...OOOOO..O..O...............................................
...............................................O...O...............O...O...O...................OOO.OOO...................O...O...O...............O...O...............................................
...............................................O..O..OOOOO...OOOOO..O..O.....................................................O..O..OOOOO...OOOOO..O..O...............................................
.................................................O..OO.O..O.O..O.OO..O.........................................................O..OO.O..O.O..O.OO..O.................................................
..........................................................O.O...........................................................................O.O..........................................................
.....................................................OO..OO.OO..OO......................O.O..O.OOO.OOO.O..O.O......................OO..OO.OO..OO.....................................................
.......................................................O..O.O..O.......................O..O.O.O.O...O.O.O.O..O.......................O..O.O..O.......................................................
.......................................................O.OO.OO.O.....O...OO............O.....................O............OO...O.....O.OO.OO.O.......................................................
.........................................................O...O......O.O.O..O..................O.......O..................O..O.O.O......O...O.........................................................
...........................................................O........O.O.OO.O.........O.O.O.O..O.......O..O.O.O.O.........O.OO.O.O........O...........................................................
..........................................................O.O.....OOO.O..O.OO.......OOO.O..O.O.........O.O..O.OOO.......OO.O..O.OOO.....O.O..........................................................
.........................................................O...O...O...O.OO..O..O.......................................O..O..OO.O...O...O...O.........................................................
..................................................................OOO.O...O..OO.......................................OO..O...O.OOO..................................................................
..........................................................OOO........O.O.....................................................O.O........OOO..........................................................
..................................................................OO...O.....................................................O...OO..................................................................
.................................................................O.O.OO.OO.O....................OO.......................O.OO.OO.O.O.................................................................
.................................................................O.......O..O..................O...OO...................O..O.......O.................................................................
...............................OOO.O..O.O.........O.O..O.OOO......OOOO...O..O.................OO.O.OOO..................O..O...OOOO......OOO.O..O.O.........O.O..O.OOO...............................
................................O.O.O.O..O.......O..O.O.O.O.........O.....O..OO...............OO.O....O...............OO..O.....O.........O.O.O.O..O.......O..O.O.O.O................................
.........................................O.......O....................O........O...................OO.O..............O........O....................O.......O.........................................
..................................O.....................O............OO.....O................O.OO.......................O.....OO............O.....................O..................................
..................................O..O.O.O.O...O.O.O.O..O....................OO..O...........O....O.OO.............O..OO....................O..O.O.O.O...O.O.O.O..O..................................
...................................O.O..O.OOO.OOO.O..O.O.......................O..O...........OOO.O.OO............O..O.......................O.O..O.OOO.OOO.O..O.O...................................
...............................................................................O..O............OO...O.............O..O...............................................................................
................................................................................O..OO.............OO............OO..O................................................................................
.....................................................................................O.........................O.....................................................................................
......................O...................OOO.OOO...................O.............O...............................O.............O...................OOO.OOO...................O......................
......................OO...................O...O...................OO..............OO..O.....................O..OO..............OO...................O...O...................OO......................
......................O....................O...O....................O................O..O.O...OO.....OO...O.O..O................O....................O...O....................O......................
.......................O.OO.....................................OO.O.................O..OOO..OOO.....OOO..OOO..O.................O.OO.....................................OO.O.......................
......................O....O..............OOO.OOO..............O....O.................O.O...................O.O.................O....O..............OOO.OOO..............O....O......................
.......................O...........................................O.....................O....OOO...OOO....O.....................O...........................................O.......................
....O..........O..........OO...................................OO......................OOO....OOO...OOO....OOO......................OO...................................OO..........O..........O....
...O.O........O.O.....OO...........................................OO..................O........O...O........O..................OO...........................................OO.....O.O........O.O...
...O.O........O.O.........O..............OO.....OO..............O......................O.....................O......................O..............OO.....OO..............O.........O.O........O.O...
.OOO.OO......OO.OOO...O....O................O.O................O....O..................OOO.................OOO.......OO.........O....O................O.O................O....O...OOO.OO......OO.OOO.
O.............O....O...OO.O............O..O.O.O.O..O............O.OO........OO...........O.................O........O...OO.......OO.O............O..O.O.O.O..O............O.OO...O.............O....O
.OOO.OO......O..OOO........O...O...O...O.O..O.O..O.O...O...O...O...........O...OO......O.....................O.....OO.O.OOO..........O...O...O...O.O..O.O..O.O...O...O...O........OOO.OO......O..OOO.
...O.OO......O..O.........OO...OOO.O........O.O........O.OOO...OO.........OO.O.OOO.....OOOO....OO...OO....OOOO.....OO.O....O........OO...OOO.O........O.O........O.OOO...OO.........O.OO......O..O...
........O..................O...O...O....OOOO...OOOO....O...O...O..........OO.O....O......OO.....O.O.O.....OO............OO.O.........O...O...O....OOOO...OOOO....O...O...O...............O...........
........OOOO...................................................................OO.O.............OO.OO.............O.OO...................................................................OOOO........
...........O...............O...O...O....OOOO...OOOO....O...O...O.........O.OO............OO.....O.O.O.....OO......O....O.OO..........O...O...O....OOOO...OOOO....O...O...O..................O........
...O..O......OO.O.........OO...OOO.O........O.O........O.OOO...OO........O....O.OO.....OOOO....OO...OO....OOOO.....OOO.O.OO.........OO...OOO.O........O.O........O.OOO...OO.........O..O......OO.O...
.OOO..O......OO.OOO........O...O...O...O.O..O.O..O.O...O...O...O..........OOO.O.OO.....O.....................O......OO...O...........O...O...O...O.O..O.O..O.O...O...O...O........OOO..O......OO.OOO.
O....O.............O...OO.O............O..O.O.O.O..O............O.OO.......OO...O........O.................O...........OO........OO.O............O..O.O.O.O..O............O.OO...O....O.............O
.OOO.OO......OO.OOO...O....O................O.O................O....O.........OO.......OOO.................OOO..................O....O................O.O................O....O...OOO.OO......OO.OOO.
...O.O........O.O.........O..............OO.....OO..............O......................O.....................O......................O..............OO.....OO..............O.........O.O........O.O...
...O.O........O.O.....OO...........................................OO..................O........O...O........O..................OO...........................................OO.....O.O........O.O...
....O..........O..........OO...................................OO......................OOO....OOO...OOO....OOO......................OO...................................OO..........O..........O....
.......................O...........................................O.....................O....OOO...OOO....O.....................O...........................................O.......................
......................O....O..............OOO.OOO..............O....O.................O.O...................O.O.................O....O..............OOO.OOO..............O....O......................
.......................O.OO.....................................OO.O.................O..OOO..OOO.....OOO..OOO..O.................O.OO.....................................OO.O.......................
......................O....................O...O....................O................O..O.O...OO.....OO...O.O..O................O....................O...O....................O......................
......................OO...................O...O...................OO..............OO..O.....................O..OO..............OO...................O...O...................OO......................
......................O...................OOO.OOO...................O.............O...............................O.............O...................OOO.OOO...................O......................
.....................................................................................O.........................O.....................................................................................
................................................................................O..OO............OO.............OO..O................................................................................
...............................................................................O..O.............O...OO............O..O...............................................................................
...................................O.O..O.OOO.OOO.O..O.O.......................O..O............OO.O.OOO...........O..O.......................O.O..O.OOO.OOO.O..O.O...................................
..................................O..O.O.O.O...O.O.O.O..O....................OO..O.............OO.O....O...........O..OO....................O..O.O.O.O...O.O.O.O..O..................................
..................................O.....................O............OO.....O.......................OO.O................O.....OO............O.....................O..................................
.........................................O.......O....................O........O..............O.OO...................O........O....................O.......O.........................................
................................O.O.O.O..O.......O..O.O.O.O.........O.....O..OO...............O....O.OO...............OO..O.....O.........O.O.O.O..O.......O..O.O.O.O................................
...............................OOO.O..O.O.........O.O..O.OOO......OOOO...O..O..................OOO.O.OO.................O..O...OOOO......OOO.O..O.O.........O.O..O.OOO...............................
.................................................................O.......O..O...................OO...O..................O..O.......O.................................................................
.................................................................O.O.OO.OO.O.......................OO....................O.OO.OO.O.O.................................................................
..................................................................OO...O.....................................................O...OO..................................................................
..........................................................OOO........O.O.....................................................O.O........OOO..........................................................
..................................................................OOO.O...O..OO.......................................OO..O...O.OOO..................................................................
.........................................................O...O...O...O.OO..O..O.......................................O..O..OO.O...O...O...O.........................................................
..........................................................O.O.....OOO.O..O.OO.......OOO.O..O.O.........O.O..O.OOO.......OO.O..O.OOO.....O.O..........................................................
...........................................................O........O.O.OO.O.........O.O.O.O..O.......O..O.O.O.O.........O.OO.O.O........O...........................................................
.........................................................O...O......O.O.O..O..................O.......O..................O..O.O.O......O...O.........................................................
.......................................................O.OO.OO.O.....O...OO............O.....................O............OO...O.....O.OO.OO.O.......................................................
.......................................................O..O.O..O.......................O..O.O.O.O...O.O.O.O..O.......................O..O.O..O.......................................................
.....................................................OO..OO.OO..OO......................O.O..O.OOO.OOO.O..O.O......................OO..OO.OO..OO.....................................................
..........................................................O.O...........................................................................O.O..........................................................
.................................................O..OO.O..O.O..O.OO..O.........................................................O..OO.O..O.O..O.OO..O.................................................
...............................................O..O..OOOOO...OOOOO..O..O.....................................................O..O..OOOOO...OOOOO..O..O...............................................
...............................................O...O...............O...O...O...................OOO.OOO...................O...O...O...............O...O...............................................
...............................................O..O..OOOOO...OOOOO..O..O...OO...................O...O...................OO...O..O..OOOOO...OOOOO..O..O...............................................
.................................................O..OO.O..O.O..O.OO..O.....O....................O...O....................O.....O..OO.O..O.O..O.OO..O.................................................
..........................................................O.O...............O.OO.....................................OO.O...............O.O..........................................................
.....................................................OO..OO.OO..OO.........O....O..............OOO.OOO..............O....O.........OO..OO.OO..OO.....................................................
...........................................O......O....O..O.O..O............O...........................................O............O..O.O..O....O......O...........................................
..........................................O.OO..OO.O...O.OO.OO.O...............OO...................................OO...............O.OO.OO.O...O.OO..OO.O..........................................
..........................................O.OO..OO.O.....O...O.............OO...........................................OO.............O...O.....O.OO..OO.O..........................................
........................................OO.OOO..OOO.OO.....O...................O..............OO.....OO..............O...................O.....OO.OOO..OOO.OO........................................
.......................................O..O........O..O...O.O..............O....O................O.O................O....O..............O.O...O..O........O..O.......................................
........................................OOO........OOO...O...O..............OO.O............O..O.O.O.O..O............O.OO..............O...O...OOO........OOO........................................
........................................OOO........OOO..........................O...O...O...O.O..O.O..O.O...O...O...O..........................OOO........OOO........................................
..............................................OO..........OOO..................OO...OOO.O........O.O........O.OOO...OO..................OOO..........OO..............................................
..............................................OO................................O...O...O....OOOO...OOOO....O...O...O................................OO..............................................
........................................OOO........OOO.........................................................................................OOO........OOO........................................
........................................OOO........OOO..........................O...O...O....OOOO...OOOO....O...O...O..........................OOO........OOO........................................
.......................................O..O........O..O........................OO...OOO.O........O.O........O.OOO...OO........................O..O........O..O.......................................
........................................OO.OOO..OOO.OO..........................O...O...O...O.O..O.O..O.O...O...O...O..........................OO.OOO..OOO.OO........................................
..........................................O.OO..OO.O........................OO.O............O..O.O.O.O..O............O.OO........................O.OO..OO.O..........................................
..........................................O.OO..OO.O.......................O....O................O.O................O....O.......................O.OO..OO.O..........................................
...........................................O......O............................O..............OO.....OO..............O............................O......O...........................................
...........................................................................OO...........................................OO...........................................................................
...............................................................................OO...................................OO...............................................................................
............................................................................O...........................................O............................................................................
...........................................................................O....O..............OOO.OOO..............O....O...........................................................................
............................................................................O.OO.....................................OO.O............................................................................
...........................................................................O....................O...O....................O...........................................................................
...........................................................................OO...................O...O...................OO...........................................................................
...........................................................................O...................OOO.OOO...................O...........................................................................
.....................................................................................................................................................................................................
.....................................................................................................................................................................................................
.....................................................................................................................................................................................................
........................................................................................O.O..O.OOO.OOO.O..O.O........................................................................................
.......................................................................................O..O.O.O.O...O.O.O.O..O.......................................................................................
.......................................................................................O.....................O.......................................................................................
..............................................................................................O.......O..............................................................................................
.....................................................................................O.O.O.O..O.......O..O.O.O.O.....................................................................................
....................................................................................OOO.O..O.O.........O.O..O.OOO....................................................................................
.....................................................................................................................................................................................................
.....................................................................................................................................................................................................
..............................................................................................O.......O..............................................................................................
.............................................................................................O.O.....O.O.............................................................................................
.............................................................................................O.O.....O.O.............................................................................................
...........................................................................................OOO.OO...OO.OOO...........................................................................................
..........................................................................................O...............O..........................................................................................
...........................................................................................OOO.OO.....OOOO...........................................................................................
.............................................................................................O.OO...OO.O.............................................................................................
.....................................................................................................................................................................................................
.................................................................................................OO..................................................................................................
..................................................................................................O..................................................................................................
..................................................................................................O..................................................................................................
..................................................................................................OO.................................................................................................
.....................................................................................................................................................................................................
.............................................................................................O.OO...OO.O.............................................................................................
...........................................................................................OOOO.....OO.OOO...........................................................................................
..........................................................................................O...............O..........................................................................................
...........................................................................................OOO.OO...OO.OOO...........................................................................................
.............................................................................................O.O.....O.O.............................................................................................
.............................................................................................O.O.....O.O.............................................................................................
..............................................................................................O.......O..............................................................................................

:elementary Not reducible to a combination of smaller parts. Elementary spaceships in particular are usually those found by search programs, and they can't be subdivided into smaller spaceships, tagalongs, and supporting reactions, as contrasted with engineered macro-spaceships.

:elementary conduit A conduit with no recognizable active signal stage besides its input and output. Theoretically an elementary conduit may become a composite conduit, if another conduit can be found that shares the beginning or end of the conduit in question. In practice this happens only rarely, because many of the most likely branch points have already been identified: glider, standard *WSS spaceship, Herschel, B-heptomino, R-pentomino, pi-heptomino, queen bee shuttle, century or bookend, dove, and wing.

:elevener (p1)

	OO....
	O.O...
	..O...
	..OOO.
	.....O
	....OO

:Elkies' p5 (p5) Found by Noam Elkies in 1997.

	.O.......
	O..OOO...
	..O......
	...O.O..O
	..OO.OOOO
	....O....
	....O.O..
	.....OO..

:emu Dave Buckingham's term for a Herschel loop that does not emit gliders (and so is "flightless"). All known Herschel loops of periods 57, 58, 59 and 61 are emus. See also Quetzal.

:emulator Any one of three p4 oscillators that produce sparks similar to those produced by LWSS, MWSS and HWSS. See LW emulator, MW emulator and HW emulator. Larger emulators are also possible, but they require stabilizing objects to suppress their non-sparks and so are of little use. The emulators were discovered by Robert Wainwright in June 1980.

:engine The active portion of an object (usually a puffer or gun) which is considered to actually produce its output, and which generally permits no variation in how it works. The other parts of the object are just there to support the engine. For examples, see puffer train, Schick engine, blinker puffer, frothing puffer and line puffer.

:engineless A rake or puffer which does not contain a specific engine for its operation. Instead it depends on perturbations of gliders or other objects by passing spaceships. The period of such objects is often adjustable, and in some cases the speed as well. An early example was the creation of c/5 rakes in September 1997, using gliders circulating among a convoy of c/5 spaceships. More recently, the passing spaceships themselves are also constructed, as in the Caterloopillar.

:en retard (p3) Found by Dave Buckingham, August 1972.

	.....O.....
	....O.O....
	OO.O.O.O.OO
	.O.O...O.O.
	O..O.O.O..O
	.OO.....OO.
	...OO.OO...
	...O.O.O...
	....O.O....
	..O.O.O.O..
	..OO...OO..

:Enterprise (c/4 diagonally, p4) Found by Dean Hickerson, March 1993.

	.......OOO...........
	.....O.OO............
	....OOOO.............
	...OO.....O..........
	..OOO..O.O.O.........
	.OO...O.O..O.........
	.O.O.OOOOO...........
	OO.O.O...O...........
	O........OO..........
	.OO..O...O.O.........
	....OO..O.OO......O..
	...........OO.....OOO
	............O..OOO..O
	............O..O..OO.
	.............O.OO....
	............OO.......
	............OO.......
	...........O.........
	............O.O......
	...........O..O......
	.............O.......

:envelope See construction envelope, reaction envelope.

:Eureka (p30) A pre-pulsar shuttle found by Dave Buckingham in August 1980. A variant is obtained by shifting the top half two spaces to either side.

	.O..............O.
	O.O....O.......O.O
	.O...OO.OO......O.
	.......O..........
	..................
	..................
	..................
	.......O..........
	.O...OO.OO......O.
	O.O....O.......O.O
	.O..............O.

:evolutionary factor For an unstable pattern, the time to stabilization divided by the initial population. For example, the R-pentomino has an evolutionary factor of 220.6, while bunnies has an evolutionary factor of 1925.777... The term is no longer in use.

:exponential filter A toolkit developed by Gabriel Nivasch in 2006, enabling the construction of patterns with asymptotic population growth matching O((log log ... log(t)) for any number of nested log operations. See also quadratic filter, recursive filter.

:exposure = underpopulation

:extensible A pattern is said to be extensible if arbitrarily large patterns of the same type can be made by repeating parts of the original pattern in a regular way.

:extra extra long = long^4

:extra long = long^3

:extremely impressive (p6) Found by Dave Buckingham, August 1976.

	....OO......
	...O.OOO....
	...O....O...
	OO.O...OO...
	OO.O.....OO.
	....OOOOO..O
	..........OO
	......O.....
	.....O.O....
	......O.....

:F116 An elementary conduit, one of the original sixteen Herschel conduits, discovered by Paul Callahan in February 1997. After 116 ticks, it produces a Herschel at (32, 1) relative to the input. Its recovery time is 138 ticks; this can be reduced to 120 ticks by adding extra mechanisms to suppress the internal glider. It is Spartan only if the following conduit is a dependent conduit, so that the welded FNG eater can be removed. A ghost Herschel in the pattern below marks the output location:

	........O..........................
	........OOO........................
	...........O.......................
	..........OO.......................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	...................................
	O..................................
	O.O.............................O..
	OOO.............................O..
	..O.............................OOO
	..................................O
	...................................
	...................................
	...................................
	...................................
	.........................OO........
	...................OO.....O........
	...................O.O.OOO.........
	............OO.......O.O...........
	............OO.......OO............

:F117 A composite conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in July 1996. It is made up of two elementary conduits, HFx58B + BFx59H. After 117 ticks, it produces a Herschel at (40, -6) relative to the input. Its recovery time is 63 ticks. It can be made Spartan by replacing the snake with an eater1 in one of two orientations. A ghost Herschel in the pattern below marks the output location:

	......................OO.....................
	.......................O.....................
	..........O...........O......................
	..........OOO.........OO.....................
	.............O...............................
	OO..........OO...............................
	.O...........................................
	.O.O.........................................
	..OO.........................................
	.........................OO...............O..
	.........................OO...............O..
	..........................................OOO
	............................................O
	.............................................
	.............................................
	..O..........................................
	..O.O........................................
	..OOO........................................
	....O...........OO...........................
	................O............................
	.................OOO.........................
	...................O.........................

:F166 An elementary conduit, one of the original sixteen Herschel conduits, discovered by Paul Callahan in May 1997. The F166 and Lx200 conduits are the two original dependent conduits (several more have since been discovered). After 166 ticks, it produces a Herschel at (49, 3) relative to the input. Its recovery time is 116 ticks. A ghost Herschel in the pattern below marks the output location:

	.................................OO.....................
	..................................O.....................
	.................................O......................
	.................................OO.....................
	........................................................
	........................................................
	.OO.....................................................
	OOO.OO..................................................
	.OO.OOO.OO..............................................
	OOO.OO..OO..........................OO...............O..
	OO..................................OO...............O..
	.....................................................OOO
	.......................................................O
	........................................................
	........................................................
	........................................................
	......OO................................................
	.....O.O......................................OO........
	.....O.........................................O........
	....OO.........................OO...........OOO.........
	...............................OO...........O...........
	........................................................
	........................................................
	.................OO.....................................
	..................O.....................................
	...............OOO......................................
	...............O........................................
	...........................OO...........................
	...........................O............................
	............................OOO.........................
	..............................O.........................
The F166 can be made Spartan by replacing the snake with an eater1 in one of two orientations. The input shown here is a Herschel great-grandparent, since the input reaction is catalysed by the transparent block before the Herschel's standard form can appear.

:F171 An elementary conduit, the seventeenth Herschel conduit, discovered by Brice Due in August 2006 in a search using only eaters as catalysts. This was the first new Herschel conduit discovery since 1998. After 171 ticks, it produces a Herschel at (29, -17) relative to the input. Its recovery time is 227 ticks, slower than many of the original sixteen conduits because of the delayed destruction of a temporary blinker, though it is clearly Spartan. A ghost Herschel in the pattern below marks the output location:

	..........O......................
	..........OOO....................
	.............O...................
	............OO...................
	.....O...........................
	.....OOO.........................
	........O........................
	.......OO........................
	.................................
	..............................O..
	....OO........................O..
	.....O........................OOO
	.....O.O........................O
	......OO.........................
	.................................
	.................................
	O................................
	OOO..............................
	...O.............................
	..OO.............................
	.................................
	.................................
	.................................
	.................................
	.................................
	.................................
	.O...............................
	.O.O.............................
	.OOO.............................
	...O.............................
	.................................
	..........OO.....................
	...........O.....................
	........OOO......................
	........O........................

:factory Another word for gun, but not used in the case of glider guns. The term is also used for a pattern that repeatedly manufactures objects other than spaceships or rakes. In this case the new objects do not move out of the way, and therefore must be used up in some way before the next one is made. The following shows an example of a p144 gun which consists of a p144 block factory whose output is converted into gliders by a p72 oscillator. (This gun is David Bell's improvement of the one Bill Gosper found in July 1994. The p72 oscillator is by Robert Wainwright, 1990, and the block factory is Achim's p144 minus one of its stabilizing blocks.)

	.......................OO........................OO
	.......................OO........................OO
	.........................................OO........
	........................................O..O.......
	.........................................OO........
	...................................................
	....................................OOO............
	....................................O.O............
	.........OO.........................OOO............
	.........OO.........................OO.............
	........O..O.......................OOO.............
	........O..O.OO....................O.O.............
	........O....OO....................OOO.............
	..........OO.OO....................................
	...............................OO..................
	.....................OO.......O..O.................
	.....................OO........OO..................
	.................................................OO
	.................................................OO
	...................................................
	....OO..................O..........................
	OO....OOOO..........OO..OO.OOO.....................
	OO..OO.OOO..........OO....OOOO.....................
	....O...................OO.........................

:familiar fours Common patterns of four identical objects. The five commonest are traffic light (4 blinkers), honey farm (4 beehives), blockade (4 blocks), fleet (4 ships, although really 2 ship-ties) and bakery (4 loaves, although really 2 bi-loaves).

:fanout A mechanism that emits two or more objects of some type for each one that it receives. Typically the objects are gliders or Herschels; glider duplicators are a special case.

:Fast Forward Force Field The following reaction found by Dieter Leithner in May 1994. In the absence of the incoming LWSS the gliders would simply annihilate one another, but as shown they allow the LWSS to advance 11 spaces in the course of the next 6 generations. A neat illusion. See also star gate. (Leithner named the Fast Forward Force Field in honour of his favourite science fiction writer, the physicist Robert L. Forward.)

	.......O......O..
	........O......OO
	..OO..OOO.....OO.
	OO.OO............
	OOOO.........O...
	.OO.........OO...
	............O.O..

:father = parent

:fd Abbreviation for full diagonals.

:featherweight spaceship = glider

:fencepost Any pattern that stabilizes one end of a wick.

:Fermat prime calculator A pattern constructed by Jason Summers in January 2000 that exhibits infinite growth if and only if there are no Fermat primes greater than 65537. The question of whether or not it really does exhibit infinite growth is therefore equivalent to a well-known and long-standing unsolved mathematical problem. It will, however, still be growing at generation 102585827975. The pattern is based on Dean Hickerson's primer and caber tosser patterns and a p8 beehive puffer by Hartmut Holzwart.

:F-heptomino Name given by Conway to the following heptomino.

	OO..
	.O..
	.O..
	.OOO

:figure-8 (p8) Found by Simon Norton in 1970.

	OOO...
	OOO...
	OOO...
	...OOO
	...OOO
	...OOO

:filter Any oscillator used to delete some but not all of the spaceships in a stream. An example is the blocker, which can be positioned so as to delete every other glider in a stream of period 8n+4, and can also do the same for LWSS streams. Other examples are the MW emulator and T-nosed p4 (either of which can be used to delete every other LWSS in a stream of period 4n+2), the fountain (which does the same for MWSS streams) and a number of others, such as the p6 pipsquirter, the pentadecathlon and the p72 oscillator shown under factory. Another example, a p4 oscillator deleting every other HWSS in a stream of period 4n+2, is shown below. (The p4 oscillator here was found, with a slightly larger stator, by Dean Hickerson in November 1994.)

	..........OOOO............
	....OO...OOOOOO...........
	OOOO.OO..OOOO.OO..........
	OOOOOO.......OO...........
	.OOOO.....................
	..........................
	................OO........
	..............O....O......
	..........................
	.............O.O..O.O.....
	...........OOOO.OO.OOOO...
	........O.O....O..O....O.O
	........OO.OO.O....O.OO.OO
	...........O.O......O.O...
	........OO.O.O......O.O.OO
	........OO.O..........O.OO
	...........O.O.OOOO.O.O...
	...........O.O......O.O...
	..........OO.O.OOOO.O.OO..
	..........O..OOO..OOO..O..
	............O..OOOO..O....
	...........OO.O....O.OO...
	...........O..O....O..O...
	............O..O..O..O....
	.............OO....OO.....

:finger A protruding cell in an oscillator or dying spark, with the ability to modify a nearby active reaction. Like a thumb, a finger cell appears at the edge of a reaction envelope and is the only live cell in its row or column. The finger spark remains alive for two ticks before dying, whereas a thumb cell dies after one tick. Because the key cell is kept alive for an extra tick, an alternate technical term is "held (orthogonal) bit spark". A "held diagonal bit spark" is not possible in B3/S23 for obvious reasons.

:fire An encoded signal used in combination with push and pull elbow operations in a simple construction arm. When a FIRE signal is sent, the construction-arm elbow produces an output glider, usually at 90 degrees from the construction arm. This terminology is generally used when there is only a single recipe for such a glider output, or only one recipe for each glider colour (e.g., FIRE WHITE, FIRE BLACK).

:fireship (c/10 orthogonally, p10) A variant of the copperhead with a trailing component that emits several large sparks, discovered by Simon Ekstrom on 20 March 2016. The interaction between the copperhead and the additional component is minimal enough that the extension technically fits the definition of a tagalong. However, the extension slightly modifies two of the phases of the spaceship, starting two ticks after the phase shown below, so it's also valid to classify the fireship as a distinct spaceship.

	....OO....
	...OOOO...
	..........
	..OOOOOO..
	...OOOO...
	..........
	..OO..OO..
	OO.O..O.OO
	...O..O...
	..........
	..........
	....OO....
	....OO....
	..........
	.O.O..O.O.
	O..O..O..O
	O........O
	O........O
	OO......OO
	..OOOOOO..

:fire-spitting (p3) Found by Nicolay Beluchenko, September 2003.

	...O......
	.OOO......
	O.........
	.O.OOO....
	.O.....O..
	..O..O....
	..O.O..O.O
	........OO

:first natural glider The glider produced at T=21 during the evolution of a Herschel. This is the most common signal output from a Herschel conduit.

:fish A generic term for LWSS, MWSS and HWSS, or, more generally, for any spaceship.

:fishhook = eater1

:fleet (p1) A common formation of two ship-ties.

	....OO....
	....O.O...
	.....OO...
	.......OO.
	OO.....O.O
	O.O.....OO
	.OO.......
	...OO.....
	...O.O....
	....OO....

:flip-flop Any p2 oscillator. However, the term is also used in two more specific (and non-equivalent) senses: (a) any p2 oscillator whose two phases are mirror images of one another, and (b) any p2 oscillator in which all rotor cells die from underpopulation. In the latter sense it contrasts with on-off. The term has also been used even more specifically for the 12-cell flip-flop shown under phoenix.

:flip-flops Another name for the flip-flop shown under phoenix.

:flipper Any oscillator or spaceship that forms its mirror image halfway through its period.

:flotilla A spaceship composed of a number of smaller interacting spaceships. Often one or more of these is not a true spaceship and could not survive without the support of the others. The following example shows an OWSS escorted by two HWSS.

	....OOOO.......
	...OOOOOO......
	..OO.OOOO......
	...OO..........
	...............
	...........OO..
	.O............O
	O..............
	O.............O
	OOOOOOOOOOOOOO.
	...............
	...............
	....OOOO.......
	...OOOOOO......
	..OO.OOOO......
	...OO..........

:fly A certain c/3 tagalong found by David Bell, April 1992. Shown here attached to the back of a small spaceship (also by Bell).

	..O...............................
	.O.O..............................
	.O.O......................O.O...O.
	.O.......................OO.O.O..O
	...........OOO........O.........O.
	OO.........OO..O.OO...O..OOOO.....
	.O.O.........OOOO..O.O..OO....OO..
	.OO........O..O...OOO.....OOO.....
	..O.......O....O..OO..OO..O..O....
	...O..O...O....O..OOO.O.O....OO...
	.......O.OO....O..OOOO.....O......
	....OO...OO....O..OOOO.....O......
	....O.O...O....O..OOO.O.O....OO...
	...OO.....O....O..OO..OO..O..O....
	....O.O....O..O...OOO.....OOO.....
	.....O.......OOOO..O.O..OO....OO..
	...........OO..O.OO...O..OOOO.....
	...........OOO........O.........O.
	.........................OO.O.O..O
	..........................O.O...O.

:flying machine = Schick engine

:FNG = first natural glider.

:fore and back (p2) Compare snake pit. Found by Achim Flammenkamp, July 1994.

	OO.OO..
	OO.O.O.
	......O
	OOO.OOO
	O......
	.O.O.OO
	..OO.OO

:forward glider A glider which moves at least partly in the same direction as the puffer(s) or spaceship(s) under consideration.

:fountain (p4) Found by Dean Hickerson in November 1994, and named by Bill Gosper. See also filter and superfountain.

	.........O.........
	...................
	...OO.O.....O.OO...
	...O.....O.....O...
	....OO.OO.OO.OO....
	...................
	......OO...OO......
	OO...............OO
	O..O...O.O.O...O..O
	.OOO.OOOOOOOOO.OOO.
	....O....O....O....
	...OO.........OO...
	...O...........O...
	.....O.......O.....
	....OO.......OO....

:fourteener (p1)

	....OO.
	OO..O.O
	O.....O
	.OOOOO.
	...O...

:fox (p2) This is the smallest asymmetric p2 oscillator. Found by Dave Buckingham, July 1977.

	....O..
	....O..
	..O..O.
	OO.....
	....O.O
	..O.O.O
	......O

:freeze-dried A term used for a glider constructible seed that can activated in some way to produce a complex object. For example, a "freeze-dried salvo" is a constellaton of constructible objects which, when triggered by a single glider, produces a unidirectional glider salvo, and nothing else. Freeze-dried salvos can be useful in slow salvo constructions, especially when an active circuit has to destroy or reconstruct itself in a limited amount of time. Gradual modification by a construction arm may be too slow, or the circuit doing the construction may itself be the object that must be modified.

The concept may be applied to other types of objects. For example, one possible way to build a gun for a waterbear would be to program a construction arm to build a freeze-dried waterbear seed, and then trigger it when the construction is complete.

:French kiss (p3) Found by Robert Wainwright, July 1971.

	O.........
	OOO.......
	...O......
	..O..OO...
	..O....O..
	...OO..O..
	......O...
	.......OOO
	.........O
For many years this was one of the best-known small oscillators with no known glider synthesis. In October 2013 Martin Grant completed a 23-glider construction.

:frog II (p3) Found by Dave Buckingham, October 1972.

	..OO...OO..
	..O.O.O.O..
	....O.O....
	...O.O.O...
	...OO.OO...
	.OO.....OO.
	O..O.O.O..O
	.O.O...O.O.
	OO.O...O.OO
	....OOO....
	...........
	...O.OO....
	...OO.O....

:frothing puffer A frothing puffer (or a frothing spaceship) is a puffer (or spaceship) whose back end appears to be unstable and breaking apart, but which nonetheless survives. The exhaust festers and clings to the back of the puffer/spaceship before breaking off. The first known frothing puffers were c/2, and most were found by slightly modifying the back ends of p2 spaceships. A number of these have periods which are not a multiple of 4 (as with some line puffers). Paul Tooke has also found c/3 frothing puffers.

The following p78 c/2 frothing puffer was found by Paul Tooke in April 2001.

	.......O.................O.......
	......OOO...............OOO......
	.....OO....OOO.....OOO....OO.....
	...OO.O..OOO..O...O..OOO..O.OO...
	....O.O..O.O...O.O...O.O..O.O....
	.OO.O.O.O.O....O.O....O.O.O.O.OO.
	.OO...O.O....O.....O....O.O...OO.
	.OOO.O...O....O.O.O....O...O.OOO.
	OO.........OO.O.O.O.OO.........OO
	............O.......O............
	.........OO.O.......O.OO.........
	..........O...........O..........
	.......OO.O...........O.OO.......
	.......OO...............OO.......
	.......O.O.O.OOO.OOO.O.O.O.......
	......OO...O...O.O...O...OO......
	......O..O...O.O.O.O...O..O......
	.........OO....O.O....OO.........
	.....OO....O...O.O...O....OO.....
	.........O.OO.O...O.OO.O.........
	..........O.O.O.O.O.O.O..........
	............O..O.O..O............
	...........O.O.....O.O...........

:frothing spaceship See frothing puffer.

:frozen = freeze-dried.

:full diagonal Diagonal distance measurement, abbreviated "fd", often appropriate when a construction arm elbow or similar diagonally-adjustable mechanism is present.

:fumarole (p5) Found by Dean Hickerson in September 1989. In terms of its 7×8 bounding box this is the smallest p5 oscillator.

	...OO...
	.O....O.
	.O....O.
	.O....O.
	..O..O..
	O.O..O.O
	OO....OO

:fuse A wick burning at one end. For examples, see baker, beacon maker, blinker ship, boat maker, cow, harvester, lightspeed wire, pi ship, reverse fuse, superstring and washerwoman. Useful fuses are usually clean, but see also reburnable fuse.

:Fx119 An elementary conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in September 1996. After 119 ticks, it produces an inverted Herschel at (20, 14) relative to the input. Its recovery time is 231 ticks; this can be reduced somewhat by suppressing the output Herschel's glider, or by adding extra catalysts to make the reaction settle more quickly. A ghost Herschel in the pattern below marks the output location:

	O......................
	O.O....................
	OOO....................
	..O....................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.........OO...........O
	....OO...OO.........OOO
	....OO..............O..
	....................O..
	.......................
	...OO..................
	....O....OO............
	.OOO.....OO............
	.O.....................

:Fx119 inserter A Herschel-to-glider converter and edge shooter based on an Fx119 Herschel conduit:

	.........O....................
	.........O.O..................
	.........OOO..................
	...........O..................
	..............................
	..............................
	..............................
	..............................
	..OO......OO..................
	...O.......O..................
	OOO.....OOO...................
	O.......O.....................
	..............................
	..............................
	..............................
	..................OO..........
	.............OO...OO..........
	.............OO...............
	..............................
	..............................
	............OO............OO..
	.............O....OO......O...
	..........OOO.....OO.......OOO
	..........O..................O

:Fx153 A composite conduit, one of the original sixteen Herschel conduits, discovered by Paul Callahan in February 1997. It is made up of two elementary conduits, HF94B + BFx59H. After 153 ticks, it produces an inverted Herschel at (48, -4) relative to the input. Its recovery time is 69 ticks. It can be made Spartan by replacing the snake with an eater1 in one of two orientations. A ghost Herschel in the pattern below marks the output location:

	.........................OO..........................
	OO........................O..........................
	.O.............OO......OOO...........................
	.O.O...........OO......O.............................
	..OO.................................................
	.....................................................
	.....................................................
	.....................................................
	....................................................O
	..................................................OOO
	.................................OO...............O..
	..O..............................OO...............O..
	..O.O................................................
	..OOO................................................
	....O................................................
	.....................................................
	.....................................................
	..............................OO.....................
	..............................O......................
	...........OO...OO.............O.....................
	............O...O.............OO.....................
	.........OOO.....OOO.................................
	.........O.........O.................................

:Fx158 An elementary conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in July 1996. After 158 ticks, it produces an inverted Herschel at (27, -5) relative to the input. Its recovery time is 176 ticks. It is the only known small conduit that does not produce its output Herschel via the usual Herschel great-grandparent, so it cannot be followed by a dependent conduit. A ghost Herschel in the pattern below marks the output location:

	.........O....OO..............
	........O.O..O.O.......OO.....
	.......O..OOOO.........O......
	.......O.O....O......O.O......
	.....OOO.OO..OO......OO.......
	....O.........................
	.O..OOOO.OO...................
	.OOO...O.OO...................
	....O.........................
	...OO.........................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	.............................O
	...........................OOO
	...........................O..
	...........................O..
	O.............................
	O.O...........................
	OOO...........................
	..O...........................
	..............................
	...............OO.............
	.........OO....O.O............
	..........O......O............
	.......OOO.......OO...........
	.......O......................

:Fx176 A composite conduit, one of the original sixteen Herschel conduits, discovered by Paul Callahan in October 1997. It is made up of three elementary conduits, HF95P + PF35W + WFx46H. After 176 ticks, it produces an inverted Herschel at (45, 0) relative to the input. Its recovery time is 92 ticks. A ghost Herschel in the pattern below marks the output location:

	..............................OO..................
	..............................OO..................
	..................................................
	.................OO...............................
	..................O...............................
	..................O.O.............................
	...................OO.............................
	..................................................
	..................................................
	..............OO..................................
	......O.......OO..................................
	......OOO.........................................
	.........O........................................
	........OO........................................
	..................................................
	OO................................................
	.O................................................
	.O.O.....................................OO.......
	..OO......................................O.......
	..........................................O.O.....
	...........................................O.O....
	............................................O...OO
	................................................OO
	..................................................
	..................................................
	..O...............................................
	..O.O...............................OO...........O
	..OOO...............................OO.........OOO
	....O..........................................O..
	...............................................O..
	..............OO........OO........................
	..............OO..OO.....O........................
	..................O.O.OOO.........................
	....................O.O...........................
	....................OO....OO......................
	.........................O.O....OO................
	.........................O......OO................
	........................OO........................

:Fx77 An elementary conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in August 1996. After 77 ticks, it produces an inverted Herschel at (25, -8) relative to the input. Its recovery time is 61 ticks; this can be reduced slightly by suppressing the output Herschel's glider, as in the L112 case. A pipsquirter can replace the blinker-suppressing eater to produce an extra glider output. It is one of the simplest known Spartan conduits, and one of the few elementary conduits in the original set of sixteen.

In January 2016, Tanner Jacobi discovered a Spartan method of extracting an extra glider output (top variant below). A ghost Herschel marks the output location for each variant.

	.O............................
	.OOO..........................
	....O.........................
	...OO...........OO...........O
	................OO.........OOO
	...........................O..
	...........................O..
	..............................
	..............................
	..............................
	..O...........................
	..O.O.........................
	..OOO.........................
	....O.........................
	..............................
	..............................
	..............................
	..............................
	..............................
	............OO......OO........
	...........O..O.....OO........
	...........O..O...............
	............OO................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	..............................
	O.............................
	OOO...........................
	...O..........................
	..OO...........OO...........O.
	...............OO.........OOO.
	..........................O...
	..........................O...
	..............................
	..............................
	..............................
	.O............................
	.O.O..........................
	.OOO..........................
	...O..........................
	..............................
	..............................
	..............................
	..............................
	..............................
	................OO............
	................O.O...........
	..................O...........
	..................OO..........

:Gabriel's p138 (p138) The following oscillator found by Gabriel Nivasch in October 2002.

	.......OOO.....
	......O..O.....
	.......O...O...
	..O.....OOO....
	...O.....O.....
	OO.OO..........
	O..O.........O.
	O.O.........O.O
	.O.........O..O
	..........OO.OO
	.....O.....O...
	....OOO.....O..
	...O...O.......
	.....O..O......
	.....OOO.......

:galaxy = Kok's galaxy

:Game of Life = Life

:Game of Life News A blog reporting on new Life discoveries, started by Heinrich Koenig in December 2004, currently found at http://pentadecathlon.com/lifenews/.

:Garden of Eden A configuration of ON and OFF cells that can only occur in generation 0. (This term was first used in connection with cellular automata by John W. Tukey, many years before Life.) It was known from the start that there are Gardens of Eden in Life, because of a theorem by Edward Moore that guarantees their existence in a wide class of cellular automata. Explicit examples have since been constructed, the first by Roger Banks, et al. at MIT in 1971. This example was 9 × 33. In 1974 J. Hardouin-Duparc et al. at the University of Bordeaux 1 produced a 6 × 122 example. The following shows a 12 × 12 example found by Nicolay Beluchenko in February 2006, based on a 13 × 12 one found by Achim Flammenkamp in June 2004.

	..O.OOO.....
	OO.O.OOOOO.O
	O.O.OO.O.O..
	.OOOO.O.OOO.
	O.O.OO.OOO.O
	.OOO.OO.O.O.
	..O...OOO..O
	.O.OO.O.O.O.
	OOO.OOOO.O.O
	OO.OOOO...O.
	.O.O.OO..O..
	.OO.O..OO.O.

Below is a 10×10 Garden of Eden found by Marijn Heule, Christiaan Hartman, Kees Kwekkeboom, and Alain Noels in 2013 using SAT-solver techniques. An exhaustive search of 90-degree rotationally symmetric 10×10 patterns was possible because the symmetry reduces the number of unknown cells by a factor of four.

	.O.OOO.O..
	..O.O.O..O
	O.OOO..OO.
	.O.OOOOO.O
	O..O..OOOO
	OOOO..O..O
	O.OOOOO.O.
	.OO..OOO.O
	O..O.O.O..
	..O.OOO.O.

Steven Eker has since found several asymmetrical Gardens of Eden that are slightly smaller than this in terms of bounding box area.

:Gemini ((5120,1024)c/33699586 obliquely, p33699586) The first self-constructing spaceship, and also the first oblique spaceship. It was made public by Andrew Wade on 18 May 2010. It was the thirteenth explicitly constructed spaceship velocity in Life, and made possible an infinite family of related velocities. The Gemini spaceship derives its name from the Latin "gemini", meaning twins, describing its two identical halves, each of which contains three Chapman-Greene construction arms. A tape of gliders continually relays between the two halves, instructing each to delete its parent and construct a daughter configuration.

:Gemini puffer See Pianola breeder.

:Geminoid A type of self-constructing circuitry that borrows key ideas from Andrew Wade's Gemini spaceship, but with several simplifications. The main feature common to the Gemini spaceship is the construction recipe encoding method. Information is stored directly, and much more efficiently, in the timings of moving gliders, rather than in a static tape with 1s and 0s encoded by the presence of small stationary objects.

Unlike the original Gemini, Geminoids have ambidextrous construction arms, initially using glider pairs on two lanes separated by 9hd, 10hd, or 0hd. The design was the basis for the linear propagator and the Demonoids. A more recent development is a Geminoid toolkit using a single-channel construction arm, which allows for the possibility of multiple elbows with no loss of efficiency, or the construction of temporary lossless elbows. Compare slow elbow.

Other new developments that could be considered part of the extended "Geminoid" toolkit include freeze-dried construction salvos and seeds, used when objects must be built within a short time window, and self-destruct circuits, which are used as an alternative to a destructor arm to clean up temporary objects in a similarly short window.

:generation The fundamental unit of time. The starting pattern is generation 0.

:germ (p3) Found by Dave Buckingham, September 1972.

	....OO....
	.....O....
	...O......
	..O.OOOO..
	..O....O..
	.OO.O.....
	..O.O.OOOO
	O.O.O....O
	OO...OOO..
	.......OO.

:gfind A program by David Eppstein which uses de Bruijn graphs to search for new spaceships. It was with gfind that Eppstein found the weekender, and Paul Tooke later used it to find the dragon. It is available at http://www.ics.uci.edu/~eppstein/ca/gfind.c (C source code only).

Compare lifesrc.

:ghost Herschel A dying spark made by removing one cell from the Herschel heptomino. This particular spark has the advantage that, when placed in a conduit to mark the location of an input or output Herschel, it disappears cleanly without damaging adjacent catalysts, even in dependent conduits with a block only two cells away.

	O..
	O..
	OOO
	..O

:GIG A glider injection gate. This is a device for injecting a glider into a glider stream. The injected glider is synthesized from one or more incoming spaceships assisted by the presence of the GIG. (This contrasts with some other glider injection reactions which do not require a GIG.) Gliders already in the glider stream pass through the GIG without interfering with it. A GIG usually consists of a small number of oscillators.

Glider injection gates are useful for building glider guns with pseudo-periods that are of the form nd, where n is a positive integer, and d is a proper divisor of some convenient base gun period (such as 30 or 46), with d > 13.

:glasses (p2) Compare scrubber and spark coil.

	....O........O....
	..OOO........OOO..
	.O..............O.
	.O..OOO....OOO..O.
	OO.O...O..O...O.OO
	...O...OOOO...O...
	...O...O..O...O...
	....OOO....OOO....
	..................
	....OO.O..O.OO....
	....O.OO..OO.O....

:glider (c/4 diagonally, p4) The smallest, most common and first discovered spaceship. This was found by Richard Guy in 1970 while Conway's group was attempting to track the evolution of the R-pentomino. The name is due in part to the fact that it is glide symmetric. (It is often stated that Conway discovered the glider, but he himself has said it was Guy. See also the cryptic reference ("some guy") in Winning Ways.)

	OOO
	O..
	.O.
The term "glider" is also occasionally (mis)used to mean "spaceship".

:glider-block cycle An infinite oscillator based on the following reaction (a variant of the rephaser). The oscillator consists of copies of this reaction displaced 2n spaces from one another (for some n>6) with blocks added between the copies in order to cause the reaction to occur again halfway through the period. The period of the resulting infinite oscillator is 8n-20. (Alternatively, in a cylindrical universe of width 2n the oscillator just consists of two gliders and two blocks.)

	...OO...
	...OO...
	........
	........
	..O..O..
	O.O..O.O
	.OO..OO.

:glider constructible See glider synthesis.

:glider construction = glider synthesis.

:glider duplicator Any reaction in which one input glider is converted into two output gliders. This can be done either by oscillators or by spaceships. The most useful glider duplicators are those with low periods.

The following period 30 glider duplicator demonstrates a simple glider duplicating mechanism found by Dieter Leithner. The input glider stream comes in from the upper left, and the output glider streams leave at the upper and lower right. One of the output glider streams is inverted, so an inline inverter is required to complete the duplicator.

	..........O.O.......................
	...........OO.......................
	...........O........................
	....................................
	....................................
	....................................
	........................OO....O.....
	..................O.....OO....OO....
	...................OO........O.O....
	..................OO................
	....................................
	....................................
	....................................
	....................................
	......................OO............
	.......................OO...........
	............O.........O.............
	............O.O.....................
	.............O.O.........OO.........
	OO...........O..O.......OOO.........
	OO...........O.O.....O.OO...........
	............O.O......O..O...........
	............O........O.OO...........
	........................OOO.....OO..
	.........................OO.....O.O.
	..................................O.
	..................................OO

Spaceship convoys which can duplicate gliders are very useful since they (along with glider turners) provide a means to clean up many dirty puffers by duplicating and turning output gliders so as to impact into the exhaust to clean it up.

Glider duplicators (and turners) are known for backward gliders using p2 c/2 spaceships, and for forward gliders using p3 c/3 spaceships. These are the most general duplicators for these speeds.

:glider gun A gun which fires gliders.

:glider injection gate = GIG

:glider lane See lane.

:gliderless A gun is said to be gliderless if it does not use gliders. The purist definition would insist that a glider does not appear anywhere, even incidentally. For a long time the only known way to construct LWSS, MWSS and HWSS guns involved gliders, and it was not until April 1996 that Dieter Leithner constructed the first gliderless gun (a p46 LWSS gun).

The following diagram shows the p44 MWSS gun that Dieter Leithner discovered (in a somewhat larger form) in April 1997. This is the smallest known gliderless gun, and also the smallest known MWSS gun. It is based on an important p44 oscillator discovered by Dave Buckingham in early 1992, shown here in an improved form found in January 2005 by Jason Summers using a new p4 sparker by Nicolay Beluchenko. Note that a glider shape appears in this gun for three consecutive generations, but always as part of a larger cluster, so even a purist would regard this gun as gliderless.

	.......O..........................................
	..OO...O.O....O...................................
	..O..OO..O.O.OO.O..OOO..OO........................
	....OO.......OO.O.O.OO..OO........................
	...OOO.......O.......OOO.........O................
	.......................O.......OOO................
	.......................O......O........OOO........
	..............................OO.......O..O.......
	.........OO..............O.............O..........
	.........OO.............O..............O...O......
	.........................OO............O..........
	........................O.O.............O.O.......
	..................................................
	.......................O.O.....OOO................
	........................O.....O..O..............OO
	OO............OOO.......O......OO...........OO.O.O
	OO...........O...O..........................OO.O..
	.............OO.OO..............................O.
	.................................OO.........OO.OO.
	..............................OO.............O.O..
	.............................................O.O..
	..............................................O...
	.............OO.OO.............O.O................
	OO...........O...O.............OO.................
	OO............OOO.................................
	...........................OO.....................
	...........................O.O....................
	.............................O....................
	.............................OO...................
	..................................................
	.........OO.......................................
	.........OO.......................................
	..................................................
	.......................O..........................
	.......................O..........................
	...OOO.......O.......OOO..........................
	....OO.......OO.O.O.OO..OO........................
	..O..OO..O.O.OO.O..OOO..OO........................
	..OO...O.O....O...................................
	.......O..........................................

:glider pair Two gliders traveling in the same direction on fixed lanes, with a specific spacetime offset. In a transceiver the preferred term is tandem glider. For several years, glider pairs were the standard building blocks in Geminoid construction arms, until the discovery of single-channel construction toolkits.

:glider pusher An arrangement of a queen bee shuttle and a pentadecathlon that can push the path of a passing glider out by one half-diagonal space. This was found by Dieter Leithner in December 1993 and is shown below. It is useful for constructing complex guns where it may be necessary to produce a number of gliders travelling on close parallel paths. See also edge shooter.

	.........OO..............
	.........OO..............
	.........................
	..........O..............
	.........O.O.............
	.........O.O.............
	..........O..............
	.........................
	.........................
	.......OO.O.OO...........
	.......O.....O...........
	........O...O............
	.O.......OOO.............
	..O......................
	OOO......................
	.........................
	.........................
	.................O....O..
	...............OO.OOOO.OO
	.................O....O..

:glider recipe = glider synthesis.

:glider reflector See reflector.

:gliders by the dozen (stabilizes at time 184) In early references this is usually shown in a larger form whose generation 1 is generation 8 of the form shown here.

	OO..O
	O...O
	O..OO

:glider synthesis Construction of an object by means of glider collisions. It is generally assumed that the gliders should be arranged so that they could come from infinity - that is, gliders should not have had to pass through one another to achieve the initial arrangement.

Glider syntheses for all still lifes and known oscillators with at most 14 cells were found by Dave Buckingham.

Perhaps the most interesting glider syntheses are those of spaceships, because these can be used to create corresponding guns and rakes. Many of the c/2 spaceships that are based on standard spaceships have been synthesized, mostly by Mark Niemiec. In June 1998 Stephen Silver found syntheses for some of the Corderships (although it was not until July 1999 that Jason Summers used this to build a Cordership gun). In May 2000, Noam Elkies suggested that a 2c/5 spaceship found by Tim Coe in May 1996 might be a candidate for glider synthesis. Initial attempts to construct a synthesis for this spaceship got fairly close, but it was only in March 2003 that Summers and Elkies managed to find a way to perform the crucial last step. Summers then used the new synthesis to build a c/2 forward rake for the 2c/5 spaceship; this was the first example in Life of a rake which fires spaceships that travel in the same direction as the rake but more slowly.

A 3-glider synthesis of a pentadecathlon is shown in the diagram below. This was found in April 1997 by Heinrich Koenig and came as a surprise, as it was widely assumed that anything using just three gliders would already be known.

	......O...
	......O.O.
	......OO..
	..........
	OOO.......
	..O.......
	.O.....OO.
	........OO
	.......O..

:glider train A certain p64 c/2 orthogonal puffer that produces two rows of blocks and two backward glider waves. Ten of these were used to make the first breeder.

	..............................O............
	...............................O...........
	.........................O.....O...........
	....O.....................OOOOOO.....OOOOOO
	.....O..............................O.....O
	O....O....................................O
	.OOOOO..............................O....O.
	......................................OO...
	...........................................
	.....................................O.....
	....................................O......
	...................................OO...OO.
	...................................O.O...OO
	....................................O...OO.
	........................................O..
	...........................................
	........................................O..
	....................................O...OO.
	...................................O.O...OO
	...................................OO...OO.
	....................................O......
	.....................................O.....
	...........................................
	......................................OO...
	.OOOOO..............................O....O.
	O....O....................................O
	.....O..............................O.....O
	....O.....................OOOOOO.....OOOOOO
	.........................O.....O...........
	...............................O...........
	..............................O............

:glider turner An reaction in which a glider is turned by an oscillator or a spaceship. In the former case, the glider turner is usually called a reflector.

Glider turners are easily built using standard spaceships. The following diagram shows a convoy which turns a forward glider 90 degrees, with the new glider also moving forwards.

	.........OO.........
	........OO.OOOO.....
	.O.......OOOOOO.....
	O.........OOOO......
	OOO.................
	....................
	....................
	....................
	....................
	...O................
	.O...O..............
	O...................
	O....O..............
	OOOOO...............
	....................
	....................
	.............OOOOOO.
	.............O.....O
	.............O......
	..............O....O
	................OO..
Small rearrangements of the back two spaceships can alternatively send the output glider into any of the other three directions.

See also glider duplicator and reflector.

:glide symmetric Undergoing simultaneous reflection and translation. A glide symmetric spaceship is sometimes called a flipper.

:Gn An abbreviation specific to converters that produce multiple gliders. A "G" followed by any integer value means that the converter produces a tandem glider -- two parallel glider outputs with lanes separated by the specified number of half diagonals.

:gnome = fox

:GoE = Garden of Eden

:GoL = Game of Life

:Golly A cross-platform open source Life program by Andrew Trevorrow and Tomas Rokicki. Unlike most Life programs it includes the ability to run patterns using the hashlife algorithm. It is available from http://golly.sourceforge.net.

:Gosper glider gun The first known gun, and indeed the first known finite pattern with unbounded growth, found by Bill Gosper in November 1970. This period 30 gun remains the smallest known gun in terms of its bounding box, though some variants of the p120 Simkin glider gun have a lower population. Gosper has since found other guns, see new gun and the p144 gun shown under factory.

	........................O...........
	......................O.O...........
	............OO......OO............OO
	...........O...O....OO............OO
	OO........O.....O...OO..............
	OO........O...O.OO....O.O...........
	..........O.....O.......O...........
	...........O...O....................
	............OO......................

:Gotts dots A 41-cell 187×39 superlinear growth pattern found by Bill Gosper in March 2006, who named it in honour of Nick Gotts, discoverer of many other low-population superlinear patterns, such as Jaws, mosquitos, teeth, catacryst and metacatacryst. Collisions within the pattern cause it to sprout its Nth switch engine at generation T = ~224n-6. The population of the pattern at time t is asymptotically proportional to t times log(t), so the growth rate is O(t ln(t)), faster than linear growth but slower than quadratic growth.

:gourmet (p32) Found by Dave Buckingham in March 1978. Compare with pi portraitor and popover.

	..........OO........
	..........O.........
	....OO.OO.O....OO...
	..O..O.O.O.....O....
	..OO....O........O..
	................OO..
	....................
	................OO..
	O.........OOO..O.O..
	OOO.......O.O...O...
	...O......O.O....OOO
	..O.O..............O
	..OO................
	....................
	..OO................
	..O........O....OO..
	....O.....O.O.O..O..
	...OO....O.OO.OO....
	.........O..........
	........OO..........

:gp = glider pair

:grammar A set of rules for connecting components together to make an object such as a spaceship, oscillator or still life.

:grandfather = grandparent

:grandparent A pattern is said to be a grandparent of the pattern it gives rise to after two generations. See also parent.

:Gray counter (p4) Found in 1971. If you look at this in the right way you will see that it cycles through the Gray codes from 0 to 3. Compare with R2D2.

	......O......
	.....O.O.....
	....O.O.O....
	.O..O...O..O.
	O.O.O...O.O.O
	.O..O...O..O.
	....O.O.O....
	.....O.O.....
	......O......

:gray ship = grey ship

:great on-off (p2)

	..OO....
	.O..O...
	.O.O....
	OO.O..O.
	....OO.O
	.......O
	....OOO.
	....O...

:grey counter = Gray counter (This form is erroneous, as Gray is surname, not a colour.)

:grey ship A spaceship that contains a region with an average density of 1/2, and which is extensible in such a way that the region of average density 1/2 can be made larger than any given square region.

See also with-the-grain grey ship, against-the-grain grey ship and hybrid grey ship.

:grin The following common parent of the block. This name relates to the infamous Cheshire cat. See also pre-block.

	O..O
	.OO.

:grow-by-one object A pattern whose population increases by one cell every generation. The smallest known grow-by-one object is the following 44-cell pattern (David Bell's one-cell improvement of a pattern found by Nicolay Beluchenko, September 2005).

	........OO.......
	.......OO........
	.........O.......
	...........OO....
	..........O......
	.................
	.........O..OO...
	.OO.....OO....O..
	OO.....O.....O...
	..O....O.O...OO..
	....O..O....OO.O.
	....OO.......OO..
	........O....O.OO
	.......O.O..O.OO.
	........O........

:growing/shrinking line ship A line ship in which the line repeatedly grows and shrinks, resulting in a high-period spaceship.

:growing spaceship An object that moves like a spaceship, except that its front part moves faster than its back part and a wick extends between the two. Put another way, a growing spaceship is a puffer whose output is burning cleanly at a slower rate than the puffer is producing it. Examples include blinker ships and pi ships.

:gull = elevener

:gun Any stationary pattern that emits spaceships (or rakes) forever. For examples see double-barrelled, edge shooter, factory, gliderless, Gosper glider gun, Simkin glider gun, new gun and true.

:gunstar Any of a series of glider guns of period 144+72n (for all non-negative integers n) constructed by Dave Buckingham in 1990 based on his transparent block reaction and Robert Wainwright's p72 oscillator (shown under factory).

:half-baked knightship ((6,3)c/2621440, p2621440) An adjustable-period, fixed-direction macro-spaceship based on the half-bakery reaction. This was the first spaceship based on this reaction, constructed in December 2014 by Adam Goucher. It moves 6 cells horizontally and 3 cells vertically every 2621440+8N ticks, depending on the relative spacing of the two halves. It is one of the slowest known knightships, and the first one that was not a Geminoid. Chris Cain optimized the design a few days later to create the Parallel HBK.

The spaceship produces gliders from near-diagonal lines of half-bakeries, which collide with each other at 180 degrees. These collisions produce monochromatic salvos that gradually build and trigger seeds, which in turn eventually construct small synchronized salvos of gliders. These re-activate the lines of half-bakeries, thus closing the cycle and moving the entire spaceship obliquely by (6,3).

:half bakery = bi-loaf.

:half-bakery reaction The key reaction used in the half-baked knightship and Parallel HBK, where a half-bakery is moved by (6,3) when a glider collides with it, and the glider continues on a new lane. Ivan Fomichev noticed in May 2014 that pairs of these reactions at the correct relative spacing can create 90-degree output gliders:

	.............................O.
	............................O..
	............................OOO
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	....................OO.........
	...................O..O........
	...................O.O.........
	.................OO.O..........
	........O.......O..O...........
	......OO........O.O............
	.......OO........O.............
	...............................
	....OO.........................
	...O..O........................
	...O.O.........................
	.OO.O..........................
	O..O...........................
	O.O............................
	.O.............................

:half diagonal A natural measurement of distance between parallel glider lanes, or between elbow locations in a universal construction arm elbow operation library. If two gliders are in the same phase and exactly lined up vertically or horizontally, N cells away from each other, then the two glider lanes are considered to be N half diagonals (hd) apart. Gliders that are an integer number of full diagonals apart must be the same colour, whereas integer half diagonals allow for both glider colours. See colour of a glider, linear propagator.

:half fleet = ship-tie

:Halfmax A pattern that acts as a spacefiller in half of the Life plane, found by Jason Summers in May 2005. It expands in three directions at c/2, producing a triangular region that grows to fill half the plane.

:hammer To hammer a LWSS, MWSS or HWSS is to smash things into the rear end of it in order to transform it into a different type of spaceship. A hammer is the object used to do the hammering. In the following example by Dieter Leithner a LWSS is hammered by two more LWSS to make it into a MWSS.

	O..O................
	....O...OO..........
	O...O..OOO.....OOOO.
	.OOOO..OO.O....O...O
	........OOO....O....
	.........O......O..O

:hammerhead A certain front end for c/2 spaceships. The central part of the hammerhead pattern is supported between two MWSS. The picture below shows a small example of a spaceship with a hammerhead front end (the front 9 columns).

	................O..
	.OO...........O...O
	OO.OOO.......O.....
	.OOOOO.......O....O
	..OOOOO.....O.OOOO.
	......OOO.O.OO.....
	......OOO....O.....
	......OOO.OOO......
	..........OO.......
	..........OO.......
	......OOO.OOO......
	......OOO....O.....
	......OOO.O.OO.....
	..OOOOO.....O.OOOO.
	.OOOOO.......O....O
	OO.OOO.......O.....
	.OO...........O...O
	................O..

:hand Any object used as a slow salvo target by a construction arm.

:handshake An old MIT name for lumps of muck, from the following form (2 generations on from the stairstep hexomino):

	..OO.
	.O.OO
	OO.O.
	.OO..

:harbor (p5) Found by Dave Buckingham in September 1978. The name is by Dean Hickerson.

	.....OO...OO.....
	.....O.O.O.O.....
	......O...O......
	.................
	.....OO...OO.....
	OO..O.O...O.O..OO
	O.O.OO.....OO.O.O
	.O.............O.
	.................
	.O.............O.
	O.O.OO.....OO.O.O
	OO..O.O...O.O..OO
	.....OO...OO.....
	.................
	......O...O......
	.....O.O.O.O.....
	.....OO...OO.....

:harvester (c p4 fuse) Found by David Poyner, this was the first published example of a fuse. The name refers to the fact the it produces debris in the form of blocks which contain the same number of cells as the fuse has burnt up.

	................OO
	...............O.O
	..............O...
	.............O....
	............O.....
	...........O......
	..........O.......
	.........O........
	........O.........
	.......O..........
	......O...........
	.....O............
	OOOOO.............
	OOOO..............
	O.OO..............

:hashlife A Life algorithm by Bill Gosper that is designed to take advantage of the considerable amount of repetitive behaviour in many large patterns of interest. It provides a means of evolving repetitive patterns millions (or even billions or trillions) of generations further than normal Life algorithms can manage in a reasonable amount of time.

The hashlife algorithm is described by Gosper in his paper listed in the bibliography at the end of this lexicon. Roughly speaking, the idea is to store subpatterns in a hash table so that the results of their evolution do not need to be recomputed if they arise again at some other place or time in the evolution of the full pattern. This does, however, mean that complex patterns can require substantial amounts of memory.

Tomas Rokicki and Andrew Trevorrow implemented Hashlife into Golly in 2005.

:hassle See hassler.

:hassler An oscillator that works by hassling (repeatedly moving or changing) some object. For some examples, see Jolson, baker's dozen, toad-flipper, toad-sucker and traffic circle.

:hat (p1) Found in 1971. See also twinhat and sesquihat.

	..O..
	.O.O.
	.O.O.
	OO.OO

:HBK = half-baked knightship

:hd Abbreviation for half diagonal. This metric is used primarily for relative measurements of glider lanes, often in relation to self-constructing circuitry; compare Gn.

:heat For an oscillator or spaceship, the average number of cells which change state in each generation. For example, the heat of a glider is 4, because 2 cells are born and 2 die every generation.

For a period n oscillator with an r-cell rotor the heat is at least 2r/n and no more than r(1-(n mod 2)/n). For n=2 and n=3 these bounds are equal.

:heavyweight emulator = HW emulator

:heavyweight spaceship = HWSS

:heavyweight volcano = HW volcano

:hebdarole (p7) Found by Noam Elkies, November 1997. Compare fumarole. The smaller version shown below was found soon after by Alan Hensel using a component found by Dave Buckingham in June 1977. The top ten rows can be stabilized by their mirror image (giving an inductor) and this was the original form found by Elkies.

	...........OO...........
	....OO...O....O...OO....
	.O..O..O.O....O.O..O..O.
	O.O.O.OO.O....O.OO.O.O.O
	.O..O..O.O.OO.O.O..O..O.
	....OO....O..O....OO....
	...........OO...........
	.......O..O..O..O.......
	......O.OO....OO.O......
	.......O........O.......
	........................
	...OO..............OO...
	...O..OOOO....OOOO..O...
	....O.O.O.O..O.O.O.O....
	...OO.O...OOOO...O.OO...
	.......OO......OO.......
	.........OO..OO.........
	.........O..O.O.........
	..........OO............

:hectic (p30) Found by Robert Wainwright in September 1984.

	......................OO...............
	......................OO...............
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.........O..........OO...OO............
	.......O.O............OOO..............
	......O.O............O...O.............
	OO...O..O.............O.O..............
	OO....O.O..............O...............
	.......O.O......O.O....................
	.........O......OO.....................
	.................O...O.................
	.....................OO......O.........
	....................O.O......O.O.......
	...............O..............O.O....OO
	..............O.O.............O..O...OO
	.............O...O............O.O......
	..............OOO............O.O.......
	............OO...OO..........O.........
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	...............OO......................
	...............OO......................

:Heisenburp device A pattern which can detect the passage of a glider without affecting the glider's path or timing. The first such device was constructed by David Bell in December 1992. The term, coined by Bill Gosper, refers to the fact that Heisenberg's Uncertainty Principle fails to apply in the Life universe. See also stable pseudo-Heisenburp.

The following is an example of the kind of reaction used at the heart of a Heisenburp device. The glider at bottom right alters the reaction of the other two gliders without itself being affected in any way.

	O.....O....
	.OO...O.O..
	OO....OO...
	...........
	...........
	...........
	.........OO
	........O.O
	..........O

:helix A convoy of standard spaceships used in a Caterpillar to move some piece of debris at the speed of the Caterpillar. The following diagram illustrates the idea. The leading edge of this example helix, represented by the glider at the upper right in the pattern below, moves at a speed of 65c/213, or slightly faster than c/4.

	...............................O.............
	.................O............OOO............
	................OOO....OOO....O.OO...........
	.........OOO....O.OO...O..O....OOO..OOO......
	.........O..O....OOO...O.......OO...O........
	.........O.......OO....O...O.........O.......
	.........O...O.........O...O.................
	OOO......O...O.........O.....................
	O..O.....O..............O.O..................
	O.........O.O................................
	O............................................
	.O.O.........................................
	.............................................
	.............................................
	..........O..................................
	.........OOO.................................
	.........O.OO................................
	..........OOO................................
	..........OO.................................
	.............................................
	.............................................
	...............OOO...........................
	...............O..O....O.....OOO.............
	...............O......OOO....O..O....O.......
	...............O.....OO.O....O......OOO......
	....OOO.........O.O..OOO.....O.....OO.O......
	....O..O.............OOO......O.O..OOO.......
	....O................OOO...........OOO.......
	....O.................OO...........OOO.......
	.....O.O............................OO.......
	...........................................O.
	..........................................OOO
	.........................................OO.O
	.........................................OOO.
	..........................................OO.
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.............................................
	.........................................O...
	..............................OOO.......OOO..
	................OOO.....O....O..O......OO.O..
	..........O....O..O....OOO......O......OOO...
	.........OOO......O....O.OO.....O......OOO...
	.........O.OO.....O.....OOO..O.O........OO...
	..........OOO..O.O......OOO..................
	.O........OOO...........OOO..................
	OOO.......OOO...........OO...................
	O.OO......OO.................................
	.OOO......................................O..
	.OO......................................OOO.
	........................................OO.O.
	........................................OOO..
	.........................................OO..
	.........OOO.................................
	........O..O.................................
	...........O.................................
	...........O.................................
	........O.O..................................

Adjustable-speed helices can produce a very wide range of spaceship speeds; see Caterloopillar.

:heptaplet Any 7-cell polyplet.

:heptapole (p2) The barberpole of length 7.

	OO........
	O.O.......
	..........
	..O.O.....
	..........
	....O.O...
	..........
	......O.O.
	.........O
	........OO

:heptomino Any 7-cell polyomino. There are 108 such objects. Those with names in common use are the B-heptomino, the Herschel and the pi-heptomino.

:Herschel (stabilizes at time 128) The following pattern which occurs at generation 20 of the B-heptomino.

	O..
	OOO
	O.O
	..O

The name is commonly ascribed to the Herschel heptomino's similarity to a planetary symbol. William Herschel discovered Uranus in 1781. However, in point of fact a Herschel bears no particular resemblance to either of the symbols used for Uranus, but does closely resemble the symbol for Saturn. So the appropriate name might actually be "Huygens" -- but "Herschel" is now universally used by tradition.

Herschels are one of the most versatile types of signal in stable circuitry. R-pentominoes and B-heptominoes naturally evolve into Herschels, and converters have also been found that change pi-heptominoes and several other signal types into Herschels, and vice versa. See elementary conduit.

:Herschel climber Any reburnable fuse reaction involving Herschels. May refer specifically to the (23,5)c/79 Herschel climber used in the waterbear, or one of several similar reactions with various velocities. See also Herschel-pair climber.

:Herschel conduit A conduit that moves a Herschel from one place to another. See also Herschel loop.

Well over a hundred simple stable Herschel conduits are currently known. As of August 2017 the number is approximately 130, depending on the precise definition of "simple" -- e.g., fitting inside a 100×100 bounding box, and producing output in no more than 300 ticks. In general a Herschel conduit can be called "simple" if its active reaction does not return to a Herschel stage except at its output. Compare elementary conduit, composite conduit.

The original universal set consisted of sixteen stable Herschel conduits, discovered between 1995 and 1998 by Dave Buckingham (DJB) and Paul Callahan (PBC). These are shown in the following table. In this table, the number in "name/steps" is the number of ticks needed to produce an output Herschel from the input Herschel. "m" tells how the Herschel is moved (R = turned right, L = turned left, B = turned back, F = unturned, f = flipped), and "dx" and "dy" give the displacement of the centre cell of the Herschel (assumed to start in the orientation shown above).

	-----------------------------------------
	name/steps  m     dx   dy     discovery
	-----------------------------------------
	R64         R    -11    9   DJB, Sep 1995
	Fx77        Ff   -25   -8   DJB, Aug 1996
	L112        L    -12  -33   DJB, Jul 1996
	F116        F    -32    1   PBC, Feb 1997
	F117        F    -40   -6   DJB, Jul 1996
	Bx125       Bf     9  -17   PBC, Nov 1998
	Fx119       Ff   -20   14   DJB, Sep 1996
	Fx153       Ff   -48   -4   PBC, Feb 1997
	L156        L    -17  -41   DJB, Aug 1996
	Fx158       Ff   -27   -5   DJB, Jul 1996
	F166        F    -49    3   PBC, May 1997
	Fx176       Ff   -45    0   PBC, Oct 1997
	R190        R    -24   16   DJB, Jul 1996
	Lx200       Lf   -17  -40   PBC, Jun 1997
	Rx202       Rf    -7   32   DJB, May 1997
	Bx222       Bf     6  -16   PBC, Oct 1998
	-----------------------------------------

See also Herschel transceiver.

:Herschel descendant A common active pattern occurring at generation 22 of a Herschel's evolution:

	OO..
	O.OO
	...O
	.O.O
	.OO.
There are other evolutionary paths leading to the same pattern, including the modification of a B-heptomino implied by generation 21 of a Herschel.

:Herschel great-grandparent A specific three-tick predecessor of a Herschel, commonly seen in Herschel conduit collections that contain dependent conduits. In some situations -- e.g., when the collection contains conduits intended to be evolved individually -- it is helpful to display the input reaction in this form instead of the standard Herschel form.

	.OO....
	OOO.OO.
	.OO.OOO
	OOO.OO.
	OO.....

Dependent conduit inputs are catalysed by a transparent block before the Herschel's standard form can appear, and before the Herschel's first natural glider is produced. This means that these conduits will fail if an actual Herschel is placed in the "correct" input location for a dependent conduit. Refer to F166 or Lx200 to see the correct relative placement of the standard transparent block catalyst.

Almost all known Herschel conduits produce a Herschel great-grandparent near the end of their evolutionary sequence. In the original universal set of Herschel conduits, Fx158 is the only exception.

:Herschel loop A cyclic Herschel track. Although no loop of length less than 256 generations has been constructed it is possible to make oscillators of smaller periods by putting more than one Herschel in the track. In this way oscillators, and in most cases guns, of all periods from 54 onwards can now be constructed (although the p55 case is a bit strange, shooting itself with gliders in order to stabilize itself). See also emu and omniperiodic.

:Herschel-pair climber Any reburnable fuse reaction involving pairs of Herschels. May refer specifically to the 31c/240 Herschel-pair climber used in the Centipede, or one of several similar reactions with various velocities. See also Herschel climber.

:Herschel receiver Any circuit that converts a tandem glider into a Herschel signal. The following diagram shows a pattern found by Paul Callahan in 1996, as part of the first stable glider reflector. Used as a receiver, it converts two parallel input gliders (with path separations of 2, 5, or 6) to an R-pentomino, which is then converted to a Herschel by one of two known mechanisms (the first of which was found by Dave Buckingham way back in 1972, and the second by Stephen Silver in October 1997). The version using Buckingham's R-to-Herschel converter is shown below.

	...............................................O.O
	......................................OO.......OO.
	......................................OO........O.
	...OO.............................................
	...O..............................................
	....O.............................................
	...OO.............................................
	............OO....................................
	...........O.O....................................
	............O..............................O......
	......................................OO...O.O....
	.....................................O..O..OO.....
	OO....................................OO..........
	OO.............................OO.................
	...............................OO.................
	..................................................
	..................................................
	..................................................
	..................................................
	..................................................
	..................................................
	............................................OO....
	............................................OO....
	........................................OO........
	........................................O.O.......
	..........................................O.......
	..........................................OO......
	.............................OO...................
	.............................OO...................
	..................................................
	..................................................
	...........................OO.....................
	...........................OO.....................

:Herschel-to-glider The largest category of elementary conduit. Gliders are very common and self-supporting, so it's much easier to find these than any other type of output signal. A large collection of these H-to-G converters has been compiled, with many different output lanes and timings. These can be used to synchronize multiple signals to produce gun patterns or complex logic circuitry. See NW31T120 for an example.

:Herschel track A track for Herschels. See also B track.

:Herschel transceiver An adjustable Herschel conduit made up of a Herschel transmitter and a Herschel receiver. The intermediate stage consists of a tandem glider -- two gliders on parallel lanes -- so that the transmitter and receiver can be separated by any required distance. The conduit may be stable, or may contain low-period oscillators.

:Herschel transmitter Any Herschel-to-two-glider converter that produces a tandem glider that can be used as input to a Herschel receiver. If the gliders are far enough apart, and if one of the gliders is used only for cleanup, then the transmitter is ambidextrous: with a small modification to the receiver, a suitably oriented mirror image of the receiver will also work.

The following diagram shows a stable Herschel transmitter found by Paul Callahan in May 1997:

	......OO...........
	.....O.O...........
	...OOO.............
	..O...O......O.....
	..OO.OO......OOO...
	.............O.O...
	...............O...
	...................
	...................
	OO.O...............
	O.OO...............
	...................
	...................
	...................
	...............OO..
	...............O...
	................OOO
	..................O
Examples of small reversible p6 and p7 transmitters are also known, and more recently several alternate Herschel transceivers have been found with different lane spacing, e.g., 0, 2, 4, 6, and 13.

:Hertz oscillator (p8) Compare negentropy, and also cauldron. Found by Conway's group in 1970.

	...OO.O....
	...O.OO....
	...........
	....OOO....
	...O.O.O.OO
	...O...O.OO
	OO.O...O...
	OO.O...O...
	....OOO....
	...........
	....OO.O...
	....O.OO...

:hexadecimal = beehive and dock

:hexaplet Any 6-cell polyplet.

:hexapole (p2) The barberpole of length 6.

	OO.......
	O.O......
	.........
	..O.O....
	.........
	....O.O..
	.........
	......O.O
	.......OO

:hexomino Any 6-cell polyomino. There are 35 such objects. For some examples see century, stairstep hexomino, table, toad and Z-hexomino.

:HF = honey farm

:H-heptomino Name given by Conway to the following heptomino. After one generation this is the same as the I-heptomino.

	OO..
	.O..
	.OOO
	..O.

:high-bandwidth telegraph (p960, p30 circuitry) A variant of the telegraph constructed by Louis-Francois Handfield in February 2017, using periodic components to achieve a transmission rate of one bit per 192 ticks. The same ten signals are sent as in the original telegraph and the p1 telegraph, but information is encoded more efficiently in the timing of those signals. Specifically, the new transmitter sends five bits every 960 ticks by adjusting the relative timings inside each of the five mirror-image paired subunits of the composite signal in the beehive-chain lightspeed wire fuse.

:highway robber Any mechanism that can retrieve a signal from a spaceship lane while allowing spaceships on nearby lanes to pass by unaffected. In practice the spaceship is generally a glider. The signal is removed from the lane, an output signal is generated elsewhere, and the highway robber returns to its original state. A competent highway robber does not affect gliders even on the lane adjacent to the affected glider stream, except during its recovery period.

A perfect highway robber doesn't affect later gliders even in the lane to which it is attached, even during its recovery period. Below is a near-perfect highway robber "bait" that requires three synchronized signals to rebuild (the Herschel, B-heptomino, and glider.) The glider at the top right passes by unharmed, but another glider following on the same lane 200 ticks later will be cleanly reflected to a new path -- and another glider following that one will also pass by unharmed. The only imperfection is a few ticks at the very end of the reconstruction, as the beehive is being rebuilt:

	......................O...........O.........
	......................OOO.......O.O.........
	.........OO...OO.........O.......OO.........
	.........OO...OO........OO..................
	............................................
	............................................
	..OO........................................
	...O........................................
	...O.O......................................
	....OO......................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	.......OO...................................
	........O...................................
	.....OOO....................................
	.....O......................................
	............................................
	............................................
	............................................
	............................................
	............................................
	............................................
	....................OO......................
	....................OO......................
	............OO..............................
	.............O..............................
	O.........OOO...............................
	OOO.......O.................................
	...O........................................
	..OO........................................
	............................................
	............................................
	............................................
	............................................
	...........O...........OO...............OO..
	.........OOO..........O.O...............OO..
	.........O.O............O...................
	.........O.....................OO.O.......O.
	...............................O.OO......OOO
	........................................OO.O
	............................................
	.............................OO.............
	.............................OO.............
	.......................OO...................
	.......................OO...................
	............................................
	............................................
	.........................OO.................
	..................OO.....OO.................
	..................OO........................

:hive = beehive

:hivenudger (c/2 orthogonally, p4) A spaceship found by Hartmut Holzwart in July 1992. (The name is due to Bill Gosper.) It consists of a pre-beehive escorted by four LWSS. In fact any LWSS can be replaced by a MWSS or a HWSS, so that there are 45 different single-hive hivenudgers.

	OOOO.....O..O
	O...O...O....
	O.......O...O
	.O..O...OOOO.
	.............
	.....OO......
	.....OO......
	.....OO......
	.............
	.O..O...OOOO.
	O.......O...O
	O...O...O....
	OOOO.....O..O
Wider versions can be made by stabilizing the front of the extended "pre-beehive", as in the line puffer shown below.
	.........O.O..................
	........O..O..................
	.......OO.....................
	......O...O...................
	.....OOO.O....................
	..OO..........................
	.O...OOOOO.......OOOO.....O..O
	O...O............O...O...O....
	O.....OO.........O.......O...O
	OOO...OOOO........O..O...OOOO.
	.O.......O....................
	.OO...................OO......
	.O.O..................OO......
	.OO..OO.O........O.O..OO......
	..O.OOO.O...O.OOOO.O..OO......
	.........OO.O.OO..O...OO...OOO
	....OOOOOO.OO...OOOO..OO...OOO
	.....O....OOO......O..OO...OOO
	......OO.....OO..OO...OO......
	.......O..O.....OOOO..OO......
	........O.O.OO.....O..OO......
	......................OO......
	..............................
	..................O..O...OOOO.
	.................O.......O...O
	.................O...O...O....
	.................OOOO.....O..O

:honeycomb (p1)

	..OO..
	.O..O.
	O.OO.O
	.O..O.
	..OO..

:honey farm (p1) A common formation of four beehives.

	......O......
	.....O.O.....
	.....O.O.....
	......O......
	.............
	.OO.......OO.
	O..O.....O..O
	.OO.......OO.
	.............
	......O......
	.....O.O.....
	.....O.O.....
	......O......

:hook Another term for a bookend. It is also used for other hook-shaped things, such as occur in the eater1 and the hook with tail, for example.

:hook with tail (p1) For a long time this was the smallest still life without a well-established name. It is now a vital component of the smallest known HWSS gun, where it acts as a rock.

	O.O..
	OO.O.
	...O.
	...OO

:houndstooth agar The p2 agar that results from tiling the plane with the following pattern.

	.OOO
	.O..
	..O.
	OOO.

:house The following induction coil. It is generation 3 of the pi-heptomino. See spark coil and dead spark coil.

	.OOO.
	O...O
	OO.OO

:H-to-G A Herschel-to-glider converter.

:H-to-MWSS A Spartan converter found by Tanner Jacobi in October 2015, which convertes an input Herschel to a middleweight spaceship. The key discovery was a very small but slightly dirty H-to-MWSS conduit, where a Herschel is catalyzed to produce an MWSS but also leaves behind a beehive. Prefixing two R64 conduits to this produces a composite converter that successfully deletes the beehive in advance, using the input Herschel's first natural glider.

	.............................OO................
	.............................OO.....OO.........
	....................................OO.........
	...............................................
	...............................................
	...............OO.................OO...........
	................O.................OO...........
	................O.O.....................OO.....
	.................OO.....................OO.....
	...............................................
	...............................................
	...............................................
	....................O..........................
	....................O.O........................
	....................OOO........................
	......................O........................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	...OO...........................OOO............
	..O.O...........................O..............
	...O...........................OO..............
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	...............................................
	.............................................OO
	.O...........................................OO
	O.O................OO.O........................
	O.O................OO.OOO......................
	.O......................O......................
	........................O...............OO.....
	........................................OO.....
	....O.O.....................................OO.
	.......O....................................OO.
	...O...O.......................................
	.......O.......................................
	....O..O..............................OO.......
	.....OOO..............................OO.......
There are many other ways to remove the beehive using a spare glider or additional conduits, but they are generally less compact than this.

:hustler (p3) Found by Robert Wainwright, June 1971.

	.....OO....
	.....OO....
	...........
	...OOOO....
	O.O....O...
	OO.O...O...
	...O...O.OO
	...O....O.O
	....OOOO...
	...........
	....OO.....
	....OO.....

:hustler II (p4)

	....O...........
	....OOO.........
	.......O........
	......O..OO.....
	O.OO.O.OO..O....
	OO.O.O.....O....
	.....O....O.....
	....O.....O.O.OO
	....O..OO.O.OO.O
	.....OO..O......
	........O.......
	.........OOO....
	...........O....

:HW emulator (p4) Found by Robert Wainwright in June 1980. See also emulator.

	.......OO.......
	..OO.O....O.OO..
	..O..........O..
	...OO......OO...
	OOO..OOOOOO..OOO
	O..O........O..O
	.OO..........OO.

:HWSS (c/2 orthogonally, p4) A heavyweight spaceship, the fourth most common spaceship. Found by Conway in 1970 by modifying a LWSS. See also MWSS.

	...OO..
	.O....O
	O......
	O.....O
	OOOOOO.

:HWSS emulator = HW emulator

:HW volcano (p5) A p5 domino sparker, found by Dean Hickerson in February 1995.

	.........O..........................
	........O.O.........................
	......OOO.O.........................
	.....O....OO.O......................
	.....O.OO...OO......OO..............
	....OO.O.OO.........O.O.............
	.........O.OOOOO......O..O.OO.......
	..O.OO.OO.O.....O....OO.O.OO.O......
	.....OO.....OOOO........O....O......
	O...O.O..O...O.O....OO.O.OOOO.OO....
	O...O.O..OO.O.OO.OO....O.O....O.O...
	.....OO...OOO.OO.O.OOO.O..OOO...O...
	..O.OO.OO.OO.............O.O..O.O.OO
	...........O......O.O.O.O..OO.O.O.O.
	....OO.O.O.OO......OO.O.O.O...O.O.O.
	.....O.OO.O..O.......O.OO..OOOO.OO..
	.....O....O.O........O...OO.........
	....OO....OO........OO...O..O.......
	...........................OO.......
At least four progressively smaller forms of this sparker have been found, including a 25-cell-wide version found by David Eppstein in 2003, and a vertically narrower 28-cell-wide version by Karel Suhajda in 2004. Scot Ellison's 17-cell-wide version is shown in the zweiback entry.

:hybrid grey ship A grey ship containing more than one type of region of density 1/2, usually a combination of a with-the-grain grey ship and an against-the-grain grey ship.

:I-heptomino Name given by Conway to the following heptomino. After one generation this is the same as the H-heptomino.

	OO..
	.O..
	.OO.
	..OO

:IMG = intermitting glider gun

:Immigration A form of colourised Life in which there are two types of ON cell, a newly-born cell taking the type of the majority of its three parent cells and surviving cells remaining of the same type as in the previous generation.

:independent conduit A Herschel conduit in which the input Herschel produces its first natural glider. Compare dependent conduit.

:induction coil Any object used to stabilize an edge (or edges) without touching. The tubs used in the Gray counter are examples, as are the blocks and snakes used in the Hertz oscillator and the heptomino at the bottom of the mathematician.

:inductor Any oscillator with a row of dead cells down the middle and whose two halves are mirror images of one another, both halves being required for the oscillator to work. The classic examples are the pulsar and the tumbler. If still lifes are considered as p1 oscillators then there are numerous simple examples such as table on table, dead spark coil and cis-mirrored R-bee. Some spaceships, such as the brain, the snail and the spider use the same principle.

:infinite glider hotel A pattern by David Bell, named after Hilbert's "infinite hotel" scenario in which a hotel with an infinite number of rooms has room for more guests even if it is already full, simply by shuffling the old guests around.

In this pattern, two pairs of Corderships moving at c/12 are pulling apart such that there is an ever-lengthening glider track between them. Every 128 generations another glider is injected into the glider track, joining the gliders already circulating there. The number of gliders in the track therefore increases without limit.

The tricky part of this construction is that even though all the previously injected gliders are repeatedly flying through the injection point, that point is guaranteed to be empty when it is time for the next glider to be injected.

:infinite growth Growth of a finite pattern such that the population tends to infinity, or at least is unbounded. Sometimes the term is used for growth of something other than population (for example, length), but here we will only consider infinite population growth. The first known pattern with infinite growth in this sense was the Gosper glider gun.

An interesting question is: What is the minimum population of a pattern that exhibits infinite growth? In 1971 Charles Corderman found that a switch engine could be stabilized by a pre-block in a number of different ways, giving 11-cell patterns with infinite growth. This record stood for more than quarter of a century until Paul Callahan found, in November 1997, two 10-cell patterns with infinite growth. The following month he found the one shown below, which is much neater, being a single cluster. This produces a stabilized switch engine of the block-laying type.

	......O.
	....O.OO
	....O.O.
	....O...
	..O.....
	O.O.....
Nick Gotts and Paul Callahan have also shown that there is no infinite growth pattern with fewer than 10 cells, so that the question has now been answered.

Also of interest is the following pattern (again found by Callahan), which is the only 5×5 pattern with infinite growth. This too emits a block-laying switch engine.

	OOO.O
	O....
	...OO
	.OO.O
	O.O.O

Following a conjecture of Nick Gotts, Stephen Silver produced, in May 1998, a pattern of width 1 which exhibits infinite growth. This pattern was very large (12470×1 in the first version, reduced to 5447×1 the following day). In October 1998 Paul Callahan did an exhaustive search, finding the smallest example, the 39×1 pattern shown below. This produces two block-laying switch engines, stability being achieved at generation 1483.

	OOOOOOOO.OOOOO...OOO......OOOOOOO.OOOOO

Although the simplest infinite growth patterns grow at a rate that is (asymptotically) linear, many other types of growth rate are possible, quadratic growth (see also breeder) being the fastest. Dean Hickerson has found many patterns with unusual growth rates, such as sawtooths and a caber tosser. Another pattern with superlinear but non-quadratic growth is Gotts dots.

See also Fermat prime calculator.

:initials = monogram

:inline inverter The following reaction in which a p30 gun can be used to invert the presence or absence of gliders in a p30 stream, with the output glider stream being in the same direction as the input glider stream.

	................O...................
	.................O..................
	...............OOO..................
	....................................
	.......................O.O..........
	.....................O...O..........
	.............O.......O..............
	............OOOO....O....O........OO
	...........OO.O.O....O............OO
	OO........OOO.O..O...O...O..........
	OO.........OO.O.O......O.O..........
	............OOOO....................
	.............O......................

:integral = integral sign

:integral sign (p1)

	...OO
	..O.O
	..O..
	O.O..
	OO...

:intentionless = elevener

:interchange (p2) A common formation of six blinkers.

	..OOO....OOO..
	..............
	O............O
	O............O
	O............O
	..............
	..OOO....OOO..

:intermediate target A temporary product of a partial slow salvo, elbow operation, or glider synthesis. An intermediate target is a useful step toward a desired outcome, but will not appear in the final construction.

:intermitting glider gun Despite the name, an intermitting glider gun (IMG) is more often an oscillator than a gun. There are two basic types. A type 1 IMG consists of two guns firing at one another in such a way that each gun is temporarily disabled on being hit by a glider from the other gun. A type 2 IMG consists of a single gun firing at a 180-degree glider reflector in such a way that returning gliders temporarily disable the gun.

Both types of IMG can be used to make glider guns of periods that are multiples of the base period. This is done by firing another gun across the two-way intermittent glider stream of the IMG in such a way that gliders only occasionally escape.

:island The individual polyplets of which a stable pattern consists are sometimes called islands. So, for example, a boat has only one island, while an aircraft carrier has two, a honey farm has four and the standard form of the eater3 has five.

:Iwona (stabilizes at time 28786) The following methuselah found by Andrzej Okrasinski in August 2004.

	..............OOO...
	....................
	....................
	....................
	....................
	....................
	..O.................
	...OO...............
	...O..............O.
	..................O.
	..................O.
	...................O
	..................OO
	.......OO...........
	........O...........
	....................
	....................
	....................
	....................
	OO..................
	.O..................

:J = Herschel

:jack (p4) Found by Robert Wainwright, April 1984.

	...O.....O...
	...OO...OO...
	O..OO...OO..O
	OOO..O.O..OOO
	.....O.O.....
	OOO..O.O..OOO
	O..OO...OO..O
	...OO...OO...
	...O.....O...

:jagged lines A pattern constructed by Dean Hickerson in May 2005 that uses puffers to produce a line of bi-blocks that weaves back and forth in a complicated way.

:jam (p3) Found by Achim Flammenkamp in 1988, but not widely known about until its independent discovery (and naming) by Dean Hickerson in September 1989. Compare with mold. In fact this is really very like caterer. In terms of its 7×7 bounding box it ties with trice tongs as the smallest p3 oscillator.

	...OO.
	..O..O
	O..O.O
	O...O.
	O.....
	...O..
	.OO...

:JavaLifeSearch See lifesrc.

:Jaws A breeder constructed by Nick Gotts in February 1997. In the original version Jaws had an initial population of 150, which at the time was the smallest for any known pattern with superlinear growth. In November 1997 Gotts produced a 130-cell Jaws using some switch engine predecessors found by Paul Callahan. Jaws has since been beaten by the even smaller mosquitoes, teeth, catacryst, metacatacryst, Gotts dots and wedge.

Jaws consists of eight pairs of switch engines which produce a new block-laying switch engine (plus masses of junk) every 10752 generations. It is therefore an MMS breeder.

:JC = dead spark coil

:JHC John Horton Conway. Also another name for monogram.

:J-heptomino = Herschel

:JLS = JavaLifeSearch

:Jolson (p15) Two blocks hassled by two pentadecathlons. Found by Robert Wainwright in November 1984 and named by Bill Gosper. A p9 version using snackers instead of pentadecathlons is also possible.

	.OO......OO..
	O..O....O..O.
	O..O....O..O.
	O..O....O..O.
	.OO......OO..
	.............
	.............
	.......O.....
	.....O..O.OO.
	......OO..OO.
	.............
	.............
	......OOOO...
	.....OOOOOO..
	....OOOOOOOO.
	...OO......OO
	....OOOOOOOO.
	.....OOOOOO..
	......OOOO...

:junk = ash.

:Justyna (stabilizes at time 26458) The following methuselah found by Andrzej Okrasinski in May 2004.

	.................O....
	................O..O..
	.................OOO..
	.................O..O.
	......................
	OO................O...
	.O................O...
	..................O...
	......................
	......................
	......................
	......................
	......................
	......................
	......................
	...................OOO
	...........OOO........

:Karel's p15 (p15) An oscillator discovered by Karel Suhajda on December 11, 2002. It consists of a period 15 rotor supported by the domino spark of a pentadecathlon. It provides accessible sparks that can be used to perturb reactions or thin signal streams.

	..O....O..
	..OOOOOO..
	..O....O..
	..........
	..........
	..........
	..OOOOOO..
	.O......O.
	O........O
	.O......O.
	..OOOOOO..

:keys See short keys, bent keys and odd keys.

:kickback = kickback reaction or 180-degree kickback.

:kickback reaction The following collision of two gliders whose product is a single glider travelling in the opposite direction to one of the original gliders. This is important in the proof of the existence of a universal constructor, and in Bill Gosper's total aperiodic, as well as a number of other constructions.

	.....O..
	......OO
	.OO..OO.
	O.O.....
	..O.....
See also 180-degree kickback.

:kidney A Gosperism for century. See also diuresis.

:killer toads A pair of toads acting together so that they can eat things. Here, for example, are some killer toads eating a HWSS. Similarly they can eat a MWSS (but not a LWSS). For another example see twirling T-tetsons II. See also candlefrobra.

	..OO.......OOO
	O....O....OOO.
	......O.......
	O.....O.......
	.OOOOOO.......
	..........OOO.
	...........OOO

:Klein bottle As an alternative to a torus, it's possible to make a finite Life universe in the form of a Klein bottle. The simplest way to do this is to use an m × n rectangle with the top edge joined to the bottom edge (as for a torus) and the left edge twisted and joined to the right.

:knightship Any spaceship of type (2m,m)/n -- that is, a spaceship of any speed that moves obliquely in a (2,1) direction. The first Conway's Life knightship was a variant of Andrew Wade's Gemini spaceship, constructed in May 2010. The next was an even slower knightship based on the half-bakery reaction. A knightship must be asymmetric and its period must be at least 6, which makes it very difficult to search for elementary knightships using programs like lifesrc.

Alternatively, the term "knightship" is regularly used to refer to any spaceship that travels neither diagonally nor orthogonally -- e.g., the original Gemini or the waterbear.

By analogy with the corresponding fairy chess pieces, spaceships of types (3m,m)/n, (3m,2m)/n and (4m,m)/n would presumably be called camelships, zebraships and giraffeships, respectively. Such spaceships do exist (see universal constructor) but small elementary versions are even more difficult to search for. No concrete example of any of these ship types has been constructed, though this could be done trivially by modifying a Gemini spaceship, or less trivially by reprogramming one of the more recent small Geminoid construction arms.

:Kok's galaxy (p8) Found by Jan Kok in 1971. See converter for a use of this sparker.

	OOOOOO.OO
	OOOOOO.OO
	.......OO
	OO.....OO
	OO.....OO
	OO.....OO
	OO.......
	OO.OOOOOO
	OO.OOOOOO

:L112 A composite conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in July 1996. It is made up of two elementary conduits, HLx53B + BFx59H. After 112 ticks, it produces a Herschel turned 90 degrees counterclockwise at (12, -33) relative to the input. Its recovery time is 61 ticks; this can be reduced slightly by removing the output glider, either with a specialized eater (as in the original true p59 gun), or with a sparker as in most of the Quetzal guns. It can be made Spartan by replacing the aircraft carrier with an eater1 in one of two orientations. A ghost Herschel in the pattern below marks the output location:

	...............OO.......
	...............O........
	.............OOO........
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	........................
	.............OO.........
	.............OO.........
	....OO..................
	....O..O................
	OO....OO................
	.O....................OO
	.O.O..................O.
	..OO................O.O.
	....................OO..
	........................
	........................
	........................
	........................
	........................
	..O.....................
	..O.O...................
	..OOO...................
	....O...................
	........................
	..............OO........
	..............OO..OO....
	..................O.O...
	....................O...
	....................OO..

:L156 A composite conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in August 1996. It is made up of three elementary conduits, HLx69R + RF28B + BFx59H. After 156 ticks, it produces a Herschel turned 90 degrees counterclockwise at (17, -41) relative to the input. Its recovery time is 62 ticks. It can be made Spartan by replacing the snake with an eater1 in one of two orientations. A ghost Herschel in the pattern below marks the output location:

	...................OO........
	...................O.........
	.................OOO.........
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.................OO..........
	.................OO..........
	.............................
	........OO.O.................
	........O.OO.................
	..........................OO.
	..........................O..
	........................O.O..
	........................OO...
	.............................
	.........O...................
	.........OOO.................
	O...........O................
	OOO........OO..............O.
	...O......................O.O
	..OO.......................O.
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	.O....................OO.....
	.O.O..................O.O....
	.OOO....................O....
	...O...........OO.......OO...
	...............O.............
	................OOO..........
	..................O..........

:lake Any still life consisting of a simple closed curve made from diagonally connected dominoes. The smallest example is the pond, and the next smallest is this (to which the term is sometimes restricted):

	....OO....
	...O..O...
	...O..O...
	.OO....OO.
	O........O
	O........O
	.OO....OO.
	...O..O...
	...O..O...
	....OO....

:lane A path traveled by a glider, or less commonly a spaceship such as a loafer. The lane is centered on the line of symmetry (if any) of the spaceship in question. If a lane is clear, then the spaceship can travel along it without colliding or interfering with any other objects.

Diagonal lanes are often numbered consecutively, in half-diagonals (hd). Occasionally diagonal lane measurements are given in quarter-diagonals (qd), in part because diagonally symmetric spaceships have a line of symmetry 1qd away from the lines available for gliders. It's also convenient that moving a glider forward by 100qd (for example) has the same effect as evolving the same glider for 100 ticks.

:Laputa (p2) Found by Rich Schroeppel, September 1992.

	...OO.OO....
	...OO.O...OO
	........O..O
	.OOOOOO.OOO.
	O..O.O......
	OO...O.OO...
	....OO.OO...

:large prime oscillator Any oscillator with a relatively small bounding box whose period is a very large prime. (If the bounding-box restriction is removed, then eight gliders travelling in a four-Snark loop would provide a trivial example for any chosen prime.) The first such oscillator was built by Gabriel Nivasch in 2003. The current record holder is an oscillator constructed by Adam P. Goucher with a period that is is a Mersenne prime with 13,395 digits (244497-1).

The next higher Mersenne-prime oscillator, period 286243-1, could be constructed with semi-Snarks and would actually be smaller than the current record holder -- but as of August 2017 the construction of this pattern has not yet been completed.

:large S = big S

:Lidka (stabilizes at time 29053) A methuselah found by Andrzej Okrasinski in July 2005.

	..........OOO..
	..........O....
	..........O...O
	...........O..O
	............OOO
	...............
	.O.............
	O.O............
	.O.............
The following variant, pointed out by David Bell, has two fewer cells and lasts two generations longer.
	..........OOO..
	...............
	...........OO.O
	............O.O
	..............O
	...............
	.O.............
	O.O............
	.O.............

:Life A 2-dimensional 2-state cellular automaton discovered by John Conway in 1970. The states are referred to as ON and OFF (or live and dead). The transition rule is as follows: a cell that is ON will remain ON in the next generation if and only if exactly 2 or 3 of the 8 adjacent cells are also ON, and a cell that is OFF will turn ON if and only if exactly 3 of the 8 adjacent cells are ON. (This is more succinctly stated as: "If 2 of your 8 nearest neighbours are ON, don't change. If 3 are ON, turn ON. Otherwise, turn OFF.")

:Life32 A freeware Life program by Johan Bontes for Microsoft Windows 95/98/ME/NT/2000/XP: https://github.com/JBontes/Life32/.

:LifeHistory A multistate CA rule equivalent to two-state B3/S23 Life, but with several additional states intended for annotation purposes. A "history" state records whether an off cell has ever turned on in the past, and other states allow on and off cells to be permanently or temporarily marked, without affecting the evolution of the pattern.

:LifeLab A shareware Life program by Andrew Trevorrow for the Macintosh (MacOS 8.6 or later): http://www.trevorrow.com/lifelab/.

:LifeLine A newsletter edited by Robert Wainwright from 1971 to 1973. During this period it was the main forum for discussions about Life. The newsletter was nominally quarterly, but the actual dates of its eleven issues were as follows:

	Mar, Jun, Sep, Dec 1971
	Sep, Oct, Nov, Dec 1972
	Mar, Jun, Sep 1973

:Lifenthusiast A Life enthusiast. Term coined by Robert Wainwright.

:lifesrc David Bell's Life search program, for finding new spaceships and oscillators. This is a C implementation of an algorithm developed by Dean Hickerson in 6502 assembler. Most of the spaceships and many of the oscillators shown in this lexicon were found with lifesrc or by Hickerson's original program.

Although lifesrc itself is a command-line program, Jason Summers has made a GUI version called WinLifeSearch for Microsoft Windows. A Java version, JavaLifeSearch, was written in November 2012 by Karel Suhajda.

The lifesrc algorithm is only useful for very small periods, as the amount of computing power required rises rapidly with increasing period. For most purposes, period 7 is the practical limit with current hardware.

Lifesrc is available from http://www.canb.auug.org.au/~dbell/ (source code only).

Compare gfind.

:LifeViewer A scriptable Javascript Life pattern viewer written by Chris Rowett, used primarily on the conwaylife.com discussion forums.

:light bulb (p2) Found in 1971.

	.OO.O..
	.O.OO..
	.......
	..OOO..
	.O...O.
	.O...O.
	..O.O..
	O.O.O.O
	OO...OO
The same rotor can be embedded in a slightly smaller stator like this:
	...O.....
	.OOO.....
	O........
	OOOOOO...
	......O..
	..O...O..
	..OO.O...
	......OOO
	........O

:lightspeed bubble A type of negative spaceship traveling through the zebra stripes agar. The center of the bubble is simple empty space, and the length and/or width of the bubble can usually be extended to any desired size.

Below is a small stabilized section of agar containing a sample lightspeed bubble, found by Gabriel Nivasch in August 1999. The bubble travels to the left at the speed of light, so it will eventually reach the edge of any finite patch and destroy itself and its supporting agar.

	.O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O...
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.............................................................O
	.OOOOOOOOOOOOO..OOO..OOO..OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O..............OO...OO...OO........O..........................
	.OOOOOOOOOOOOO...OO...OO...O.OO.O....OOOOOOOOOOOOOOOOOOOOOOOO.
	.............................OO.....O........................O
	.OOOOOOOOOOOOO.................OOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...............................O.............................
	.OOOOOOOOOOOOO...................OOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.................................O....O......................O
	.OOOOOOOOOOOOO...................OO....OOOOOOOOOOOOOOOOOOOOOO.
	O................................O.....O....O.................
	.OOOOOOOOOOOOO...................OO....OO....OOOOOOOOOOOOOOOO.
	.................................O.....O.....O....O..........O
	.OOOOOOOOOOOOO...................OO....OO....OO....OOOOOOOOOO.
	O................................O.....O.....O.....O....O.....
	.OOOOOOOOOOOOO...................OO....OO....OO....OO....OOOO.
	.................................O.....O.....O.....O.....O...O
	.OOOOOOOOOOOOO...................OO....OO....OO....OO....OOOO.
	O................................O.....O.....O.....O....O.....
	.OOOOOOOOOOOOO...................OO....OO....OO....OOOOOOOOOO.
	.................................O.....O.....O....O..........O
	.OOOOOOOOOOOOO...................OO....OO....OOOOOOOOOOOOOOOO.
	O................................O.....O....O.................
	.OOOOOOOOOOOOO...................OO....OOOOOOOOOOOOOOOOOOOOOO.
	.................................O....O......................O
	.OOOOOOOOOOOOO...................OOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...............................O.............................
	.OOOOOOOOOOOOO.................OOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.............................OO.....O........................O
	.OOOOOOOOOOOOO...OO...OO...O.OO.O....OOOOOOOOOOOOOOOOOOOOOOOO.
	O..............OO...OO...OO........O..........................
	.OOOOOOOOOOOOO..OOO..OOO..OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.............................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O...

An open problem related to lightspeed bubbles was whether large extensible empty areas could be created whose length was not proportional to the width (as it must be in the above case, due to the tapering back edge). This was solved in February 2017 by Arie Paap; a simple period-2 solution is shown below.

	...O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O...
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...........................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.............................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O.....................................................O.....O
	.OOOOOOOOOOOOOOOOOOOO..OOO..OOO..OOO..OOOOOOOO..OOOO...OOOOO.
	......................OO...OO...OO...OO........OO.....O......
	.OOOOOOOOOOOOOOOOOOOO...OO...OO...OO...OOOOOOO...O.OO..OOOOO.
	O.........................................O........OO.......O
	.OOOOOOOOOOOOOOOOOOOO......................OO.O......OOOOOOO.
	...........................................O............O....
	.OOOOOOOOOOOOOOOOOOOO......................O.............OOO.
	O..........................................OO.....OO....O...O
	.OOOOOOOOOOOOOOOOOOOO......................OO...OO...O.OOOOO.
	...........................................O..O.OO...O.......
	.OOOOOOOOOOOOOOOOOOOO......................O......OO...OOOOO.
	O..........................................OO..........O....O
	.OOOOOOOOOOOOOOOOOOOO......................OO..........OOOOO.
	...........................................O......OO.O.......
	.OOOOOOOOOOOOOOOOOOOO......................O..O.OO...O.OOOOO.
	O..........................................OO...OO......O...O
	.OOOOOOOOOOOOOOOOOOOO......................OO.....OO.....OOO.
	...........................................O............O....
	.OOOOOOOOOOOOOOOOOOOO......................O...........OOOOO.
	O..........................................OO.....OO.OO.....O
	.OOOOOOOOOOOOOOOOOOOO......................OO...OO...OO..OOO.
	...........................................O..O.OO.....OO....
	.OOOOOOOOOOOOOOOOOOOO......................O......OO....OOOO.
	O..........................................OO...............O
	.OOOOOOOOOOOOOOOOOOOO......................OO...........OOOO.
	...........................................O......OO...OO....
	.OOOOOOOOOOOOOOOOOOOO......................O..O.OO...OO..OOO.
	O..........................................OO...OO...OO.....O
	.OOOOOOOOOOOOOOOOOOOO......................OO.....OO...OOOOO.
	...........................................O............O....
	.OOOOOOOOOOOOOOOOOOOOOO.....O.....O.....O..O.O...........OOO.
	O.........................OO....OO....OO...O...O.O.......O..O
	.OOOOOOOOOOOOOOOOOOOOOOOO.OO.OO.OO.OO.OO.OOOOOOOOO.......OOO.
	........................................................O....
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO...OOOOOOO.
	O..................................................OO.......O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO..OOOOOOOO.
	.............................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O...........................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	...O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O...

:lightspeed ribbon = superstring

:lightspeed telegraph = telegraph.

:lightspeed wire Any wick that can burn non-destructively at the speed of light. These are potentially useful for various things,but so far the necessary mechanisms are very large and unwieldy. In October 2002, Jason Summers discovered a lightspeed reaction traveling through an orthogonal chain of beehives: Summers completed a period-1440 lightspeed telegraph based on this reaction in 2003.

	...O...........................................................
	.O...O.........................................................
	.O....O....OO.OO...............................................
	O......O...OOOOOO...OO...OO...OO...OO...OO...OO...OO...OO...OO.
	O......O..O......O.O..O.O..O.O..O.O..O.O..O.O..O.O..O.O..O.O..O
	OO.....O...OOOOOO...OO...OO...OO...OO...OO...OO...OO...OO...OO.
	......O....OO.OO...............................................
	....O..........................................................

A stable lightspeed transceiver mechanism using this same signal reaction, the p1 telegraph, was constructed by Adam P. Goucher in 2010; the bounding boxes of both the transmitter and receiver are over 5000 cells on a side. A more compact periodic high-bandwidth telegraph with a much improved transmission rate was completed by Jean-Francois Handfield in 2017.

The following diagram shows an older example of a lightspeed wire, with a small defect that travels along it at the speed of light. As of this writing (August 2017) no method has been found of creating such a defect in the upstream end of this particular stable wire, or of non-destructively detecting the arrival of the defect and repairing the wire at the downstream end.

	....OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO....
	....OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO....
	..........................................................
	..OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO..
	.O......O...............................................O.
	O.OOOOO....OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.O
	.O.....O................................................O.
	..OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO..
	..........................................................
	....OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO....
	....OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO..OO....

:lightweight emulator = LW emulator

:lightweight spaceship = LWSS

:lightweight volcano = toaster

:linear growth A growth rate proportional to T, where T is the number of ticks that a pattern has been run. Compare superlinear growth, quadratic growth.

:linear propagator A self-replicating pattern in which each copy of a pattern produces one child that is an exact copy of itself. The child pattern then blocks the parent from any further replication. An example was constructed by Dave Greene on 23 November 2013, with a construction arm using two glider lanes separated by 9hd. By some definitions, due to its limited one-dimensional growth pattern, the linear propagator is not a true replicator, Compare quadratic replicator.

:line-cutting reaction A reaction that can cut an infinite diagonal line of cells, leaving a gap with both ends sealed.

:line puffer A puffer which produces its output by means of an orthogonal line of cells at right angles to the direction of travel. The archetypal line puffer was found by Alan Hensel in March 1994, based on a spaceship found earlier that month by Hartmut Holzwart. The following month Holzwart found a way to make extensible c/2 line puffers, and Hensel found a much smaller stabilization the following day. But in October 1995 Tim Coe discovered that for large widths these were often unstable, although typically lasting millions of generations. In May 1996, however, Coe found a way to fix the instability. The resulting puffers appear to be completely stable and to exhibit an exponential increase in period as a function of width, although neither of these things has been proved.

Line puffers have enabled the construction of various difficult periods for c/2 spaceships and puffers, including occasionally periods which are not multiples of 4 and which would therefore be impossible to attain with the usual type of construction based on standard spaceships. (See frothing puffer for another method of constructing such periods.) In particular, the first c/2 rake with period not divisible by 4 was achieved in January 2000 when David Bell constructed a p42 backrake by means of line puffers.

See also hivenudger and puff suppressor.

:line ship A spaceship in which the front end is a linestretcher, the line being eaten by the back end.

:linestretcher A wickstretcher that stretches a single diagonal line of cells. The first example was constructed by Jason Summers in March 1999; this was c/12 and used switch engine based puffers found earlier by Dean Hickerson. The first c/4 example was found by Hartmut Holzwart in November 2004.

:loading dock (p3) Found by Dave Buckingham, September 1972.

	....O....
	..OOO....
	.O...OO..
	O.OO...O.
	.O...OO.O
	..OO...O.
	....OOO..
	....O....

:loaf (p1)

	.OO.
	O..O
	.O.O
	..O.

:loafer (c/7 orthogonally, p7) A small c/7 spaceship discovered by Josh Ball on 17 February 2013:

	.OO..O.OO
	O..O..OO.
	.O.O.....
	..O......
	........O
	......OOO
	.....O...
	......O..
	.......OO

It has a known 8-glider construction recipe, probably not minimal, discovered on the following day:

	.................................O
	...............................OO.
	................................OO
	.........O........................
	.O........O.......................
	..O.....OOO.......................
	OOO...............................
	..................................
	..................................
	.....O............................
	......O...........................
	....OOO...........................
	........................O.O.......
	.........................OO.......
	.........................O........
	..................................
	...........................O.O....
	...........................OO.....
	............................O.....
	...............................OOO
	...............................O..
	................................O.
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	.....OO...........................
	......OO..........................
	.....O............................
The loafer was therefore the first new glider-constructible spaceship in almost a decade. (A glider synthesis for a 2c/5 ship, 60P5H2V0, was found in March 2003.)

:loaflipflop (p15) Here four pentadecathlons hassle a loaf. Found by Robert Wainwright in 1990.

	................O.................
	...............OOO................
	..................................
	..................................
	...............OOO................
	..................................
	...............O.O................
	...............O.O................
	..................................
	...............OOO................
	..................................
	..................................
	...............OOO................
	................O.................
	..................................
	.O..O.OO.O..O...............OO....
	OO..O....O..OO...OO.......O....O..
	.O..O.OO.O..O...O..O.....O......O.
	................O.O.....O........O
	.................O......O........O
	........................O........O
	.........................O......O.
	..........................O....O..
	............................OO....
	..................OOO.............
	.................O...O............
	................O.....O...........
	..................................
	...............O.......O..........
	...............O.......O..........
	..................................
	................O.....O...........
	.................O...O............
	..................OOO.............

:loaf on loaf = bi-loaf

:loaf pull The following glider/loaf collision, which pulls a loaf (3,1) toward the glider source:

	.O.....
	O.O....
	O..O...
	.OO....
	.......
	.......
	....OOO
	....O..
	.....O.

:loaf siamese barge (p1)

	..OO.
	.O..O
	O.O.O
	.O.O.
	..O..

:lobster (c/7 diagonally, p7) A spaceship discovered by Matthias Merzenich in August 2011, the first diagonally traveling c/7 spaceship to be found. It consists of two gliders pulling a tagalong that then rephases them.

	............OOO...........
	............O.............
	.............O..OO........
	................OO........
	............OO............
	.............OO...........
	............O..O..........
	..........................
	..............O..O........
	..............O...O.......
	...............OOO.O......
	....................O.....
	OO..O.O.............O.....
	O.O.OO.............O......
	O....O..OO.............OO.
	......O...O......OO..OO..O
	..OO......O......O..O.....
	..OO....O.O....OO.........
	.........O.....O...O...O..
	..........O..O....OO......
	...........OO...O.....O.O.
	...............O........OO
	...............O....O.....
	..............O...O.......
	..............O.....OO....
	...............O.....O....

:logarithmic growth A pattern whose population or bounding box grows no faster than logarithmically, asymptotic to n.log(t) for some constant n. The first such pattern constructed was the caber tosser whose population is logarithmic, but whose bounding box still grows linearly. The first pattern whose bounding box and population both grow logarithmically was constructed by Jason Summers with Gabriel Nivasch in 2003. For a pattern with a slower growth rate than this, see Osqrtlogt.

:LoM = lumps of muck

:lone dot agar An agar in which every live cell is isolated in every generation.

:lonely bee = worker bee

:long A term applied to an object that is of the same basic form as some standard object, but longer. For examples see long barge, long boat, long bookend, long canoe, long shillelagh, long ship and long snake.

:long^3 The next degree of longness after long long. Some people prefer "extra long".

:long^4 The next degree of longness after long^3. Some people prefer "extra extra long".

:long barge (p1)

	.O...
	O.O..
	.O.O.
	..O.O
	...O.

:long boat (p1)

	.O..
	O.O.
	.O.O
	..OO

:long bookend The following induction coil, longer than a bookend.

	...OO
	O...O
	OOOO.

:long canoe (p1)

	....OO
	.....O
	....O.
	...O..
	O.O...
	OO....

:long hat = loop

:long hook = long bookend

:long house = dock

:long integral (p1)

	..OO
	.O.O
	.O..
	..O.
	O.O.
	OO..

:long long The next degree of longness after long. Some people prefer "very long".

:long long barge (p1)

	.O....
	O.O...
	.O.O..
	..O.O.
	...O.O
	....O.

:long long boat (p1)

	.O...
	O.O..
	.O.O.
	..O.O
	...OO

:long long canoe (p1)

	.....OO
	......O
	.....O.
	....O..
	...O...
	O.O....
	OO.....

:long long ship (p1)

	OO...
	O.O..
	.O.O.
	..O.O
	...OO

:long long snake (p1)

	OO....
	O.O...
	...O.O
	....OO

:long shillelagh (p1)

	OO..OO
	O..O.O
	.OO...

:long ship (p1)

	OO..
	O.O.
	.O.O
	..OO

:long sinking ship = long canoe

:long snake (p1)

	OO...
	O.O.O
	...OO

:loop (p1)

	.OO..
	O..O.
	.O.O.
	OO.OO

:low-density Life = sparse Life

:lumps of muck The common evolutionary sequence that ends in the blockade. The name is sometimes used of the blockade itself, and can in general be used of any stage of the evolution of the stairstep hexomino.

:LW emulator (p4) The smallest (and least useful) emulator, found by Robert Wainwright in June 1980.

	..OO.O..O.OO..
	..O........O..
	...OO....OO...
	OOO..OOOO..OOO
	O..O......O..O
	.OO........OO.

:LWSS (c/2 orthogonally, p4) A lightweight spaceship, the smallest known orthogonally moving spaceship, and the second most common (after the glider). Found by Conway when one formed from a random soup in 1970. See also MWSS and HWSS.

	.O..O
	O....
	O...O
	OOOO

:LWSS emulator = LW emulator

:LWSS-to-G See 135-degree MWSS-to-G.

:LWTDS Life Worker Time Deficiency Syndrome. Term coined by Dieter Leithner to describe the problem of having to divide scarce time between Life and real life.

:LW volcano = toaster

:Lx200 A composite conduit, one of the original sixteen Herschel conduits, discovered by Paul Callahan in June 1997. It is made up of two elementary conduits, HL141B + BFx59H. The Lx200 and F166 conduits are the two original dependent conduits (several more have since been discovered.) After 200 ticks, it produces an inverted Herschel turned 90 degrees counterclockwise at (17, -40) relative to the input. Its recovery time is 90 ticks. It can be made Spartan by replacing the snakes with eater1s in one of two orientations. A ghost Herschel in the pattern below marks the output location:

	.....................OO.............
	......................O.............
	......................OOO...........
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	.......................OO...........
	.......................OO...........
	....................................
	..............................O.OO..
	..............................OO.O..
	....................................
	....................................
	..............O.OO..................
	..............OO.O..................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	....................................
	................................OO..
	................................O.O.
	.OO...............................O.
	OOO.OO............................OO
	.OO.OOO.OO..........................
	OOO.OO..OO..........................
	OO..................................
	....................................
	....................................
	....................................
	................................OO..
	................................OO..
	....................................
	......OO............................
	.......O............................
	....OOO.........................OO..
	....O...........................OO..
	..................OO................
	.................O.O................
	.................O..................
	................OO........OO........
	..........................O.........
	...........................OOO......
	.............................O......
The input shown here is a Herschel great-grandparent, since the input reaction is catalysed by the transparent block before the Herschel's standard form can appear.

:macro-spaceship A self-constructing or self-supporting spaceship, such as the Caterpillar, Centipede, half-baked knightship, waterbear, Demonoid, Orthogonoid, and Caterloopillar. Engineered spaceships of these types are inevitably large and complex.

:mango (p1)

	.OO..
	O..O.
	.O..O
	..OO.

:mathematician (p5) Found by Dave Buckingham, 1972.

	....O....
	...O.O...
	...O.O...
	..OO.OO..
	O.......O
	OOO...OOO
	.........
	OOOOOOOOO
	O.......O
	...OOOO..
	...O..OO.

:Max A name for the smallest known spacefiller. The name represents the fact that the growth rate is the fastest possible. (This has not quite been proved, however. There remains the possibility, albeit not very likely, that a periodic agar could have an average density greater than 1/2, and a spacefiller stretching such an agar at the same speed as the known spacefillers would have a faster average growth rate.)

:mazing (p4) In terms of its minimum population of 12 this ties with mold as the smallest p4 oscillator. Found by Dave Buckingham in December 1973. For some constructions using mazings, see popover and sixty-nine.

	...OO..
	.O.O...
	O.....O
	.O...OO
	.......
	...O.O.
	....O..

:medium fish = MWSS

:megacell = p1 megacell.

:metacatacryst A 52-cell pattern exhibiting quadratic growth. Found by Nick Gotts, December 2000. This was for some time the smallest known pattern (in terms of initial population) with superlinear growth. See also catacryst for more recent record-holders.

:metacell CA logic circuitry that emulates the behavior of a single cell. The circuitry is hard-wired to emulate a particular CA rule, but changing the rule is usually a matter of making simple adjustments. Known examples include David Bell's original 500×500 unit cell, Jared Prince's Deep Cell, Brice Due's OTCA metapixel, and Adam P. Goucher's megacell.

:metamorphosis An oscillator built by Robert Wainwright that uses the following reaction (found by Bill Gosper) to turn gliders into LWSS, and converts these LWSS back into gliders by colliding them head on. (There are in fact two ways to do the following reaction, because the spark of the twin bees shuttle is symmetric.)

	...................O.........
	....................O........
	..................OOO........
	.............................
	.............................
	.............................
	.............................
	.............................
	............O...O.....O.OO...
	OO.........O.....O....O.O.O..
	OO.........O.........O....O..
	...........OO...O.....O.O.O..
	.............OOO......O.OO...
	.............................
	.............OOO.............
	...........OO...O............
	OO.........O...............OO
	OO.........O.....O.........OO
	............O...O............

:metamorphosis II An oscillator built by Robert Wainwright in December 1994 based on the following p30 glider-to-LWSS converter. This converter was first found by Paul Rendell, January 1986 or earlier, but wasn't widely known about until Paul Callahan rediscovered it in December 1994.

	......................O.
	.....................O..
	.....................OOO
	........................
	........................
	.........O.O............
	.........O..O...........
	OO..........OO..........
	OO........O...OO........
	.....OO.....OO..........
	....O....O..O...........
	.........O.O............
	........................
	........................
	........................
	........................
	................O.......
	...............OOO......
	..............OOOOO.....
	.............O.O.O.O....
	.............OO...OO....
	........................
	........................
	................O.......
	...............O.O......
	...............O.O......
	................O.......
	...............OO.......
	...............OO.......
	...............OO.......

:metapixel See metacell, OTCA metapixel.

:methuselah Any small pattern that stabilizes only after a long time. Term coined by Conway. Examples include rabbits, acorn, the R-pentomino, blom, Iwona, Justyna and Lidka. See also ark.

:Mickey Mouse (p1) A name proposed by Mark Niemiec for the following still life:

	.OO....OO.
	O..O..O..O
	O..OOOO..O
	.OO....OO.
	...OOOO...
	...O..O...
	....OO....

:middleweight emulator = MW emulator

:middleweight spaceship = MWSS

:middleweight volcano = MW volcano

:mini pressure cooker (p3) Found by Robert Wainwright before June 1972. Compare pressure cooker.

	.....O.....
	....O.O....
	....O.O....
	...OO.OO...
	O.O.....O.O
	OO.O.O.O.OO
	...O...O...
	...O.O.O...
	....O.O....
	.....O.....

:M.I.P. value The maximum population divided by the initial population for an unstable pattern. For example, the R-pentomino has an M.I.P. value of 63.8, since its maximum population is 319. The term is no longer in use.

:MIT oscillator = cuphook

:MMM breeder See breeder.

:MMS breeder See breeder.

:mod The smallest number of generations it takes for an oscillator or spaceship to reappear in its original form, possibly subject to some rotation or reflection. The mod may be equal to the period, but it may also be a quarter of the period (for oscillators that rotate 90 degrees every quarter period) or half the period (for other oscillators which rotate 180 degrees every half period, and also for flippers).

:mold (p4) Found by Achim Flammenkamp in 1988, but not widely known until Dean Hickerson rediscovered it (and named it) in August 1989. Compare with jam. In terms of its minimum population of 12 it ties with mazing as the smallest p4 oscillator. But in terms of its 6×6 bounding box it wins outright. In fact, of all oscillators that fit in a 6×7 box it is the only one with period greater than 2.

	...OO.
	..O..O
	O..O.O
	....O.
	O.OO..
	.O....

:monochromatic salvo A slow salvo that uses gliders of only one colour. For example, the slow salvos generated by half-baked knightships are monochromatic, because they are generated by a single type of reaction which can happen at any position along a diagonal line. The smallest possible step size is one full diagonal (1fd), which is two half diagonals (2hd), which means that any single glider-producing reaction can only reach half of the available glider lanes. See colour of a glider.

:monogram (p4) Found by Dean Hickerson, August 1989.

	OO...OO
	.O.O.O.
	.OO.OO.
	.O.O.O.
	OO...OO

:monoparity salvo A slow salvo that uses gliders of only one parity. Compare monochromatic salvo.

:Moore neighbourhood The set of all cells that are orthogonally or diagonally adjacent to a cell or group of cells. The von Neumann neighbourhood of a cell can be thought of as the points at a Chebyshev distance of 1 from that cell. Compare von Neumann neighbourhood. The Conway's Life rule is based on the Moore neighborhood, as are all the "Life-like" rules and many other commonly investigated rule families.

Cell neighbourhoods can also be defined with a higher range. The Moore neighbourhood of range n can be defined recursively as the Moore neighbourhood of the Moore neighbourhood of range n-1. For example, the Moore neighbourhood of range 2 includes all cells that are orthogonally or diagonally adjacent to the standard Moore neighbourhood.

:moose antlers (p1)

	OO.....OO
	O.......O
	.OOO.OOO.
	...O.O...
	....O....

:mosquito See mosquito1, mosquito2. mosquito3, mosquito4 and mosquito5.

:mosquito1 A breeder constructed by Nick Gotts in September 1998. The original version had an initial population of 103, which was then the smallest for any known pattern with superlinear growth (beating the record previously held by Jaws). This was reduced to 97 by Stephen Silver the following month, but was then almost immediately superseded by mosquito2.

Mosquito1 consists of the classic puffer train plus four LWSS and four MWSS (mostly in predecessor form, to keep the population down). Once it gets going it produces a new block-laying switch engine (plus a lot of junk) every 280 generations. It is therefore an MMS breeder, albeit a messy one.

:mosquito2 A breeder constructed by Nick Gotts in October 1998. Its initial population of 85 was for a couple of hours the smallest for any known pattern with superlinear growth, but was then beaten by mosquito3.

Mosquito2 is very like mosquito1, but uses two fewer MWSS and one more LWSS.

:mosquito3 A breeder constructed by Nick Gotts in October 1998. Its initial population of 75 was at the time the smallest for any known pattern with superlinear growth, but was beaten a few days later by mosquito4.

Mosquito3 has one less LWSS than mosquito2. It is somewhat different from the earlier mosquitoes in that the switch engines it makes are glider-producing rather than block-laying.

:mosquito4 A slightly improved version of mosquito3 which Stephen Silver produced in October 1998 making use of another discovery of Nick Gotts (September 1997): an 8-cell pattern that evolves into a LWSS plus some junk. Mosquito4 is a breeder with an initial population of 73, at the time the smallest for any known pattern with superlinear growth, but superseded a few days later by mosquito5.

:mosquito5 A slightly improved version of mosquito4 which Nick Gotts produced in October 1998. The improvement is of a similar nature to the improvement of mosquito4 over mosquito3. Mosquito5 is a breeder with an initial population of 71. At the time, this was the smallest population for any known pattern with superlinear growth, but it has since been superseded by teeth, catacryst, metacatacryst, Gotts dots and wedge.

:mould = mold

:moving sawtooth A sawtooth such that no cell is ON for more than a finite number generations. David Bell has constructed patterns of this type, with a c/2 front end and a c/3 back end.

:MSM breeder See breeder.

:multi-state Life = colourised Life

:multum in parvo (stabilizes at time 3933) A methuselah found by Charles Corderman, but not as long-lasting as his acorn.

	...OOO
	..O..O
	.O....
	O.....

:muttering moat Any oscillator whose rotor consists of a closed chain of cells each of which is adjacent to exactly two other rotor cells. Compare babbling brook. Examples include the bipole, the blinker, the clock, the cuphook, the Gray counter, the quad, the scrubber, the skewed quad and the p2 snake pit. The following diagram shows a p2 example (by Dean Hickerson, May 1993) with a larger rotor. See ring of fire for a very large one.

	OO.....
	O.O.OO.
	.....O.
	.O..O..
	..O....
	..O.O.O
	.....OO

:MW emulator (p4) Found by Robert Wainwright in June 1980. See also emulator and filter.

	.......O.......
	..OO.O...O.OO..
	..O.........O..
	...OO.....OO...
	OOO..OOOOO..OOO
	O..O.......O..O
	.OO.........OO.

:MWSS (c/2 orthogonally, p4) A middleweight spaceship, the third most common spaceship. Found by Conway in 1970 by modifying a LWSS. See also HWSS.

	...O..
	.O...O
	O.....
	O....O
	OOOOO.

:MWSS emulator = MW emulator

:MWSS out of the blue The following reaction, found by Peter Rott in November 1997, in which a LWSS passing by a p46 oscillator creates a MWSS travelling in the opposite direction. Together with some reactions found by Dieter Leithner, and a LWSS-turning reaction which Rott had found in November 1993 (but which was not widely known until Paul Callahan rediscovered it in June 1994) this can be used to prove that there exist gliderless guns for LWSS, MWSS and HWSS for every period that is a multiple of 46.

	O..O.................................
	....O................................
	O...O................................
	.OOOO................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	...................OO..............OO
	..................OO...............OO
	...................OOOOO.............
	..OO................OOOO.............
	..OO.....O...........................
	........OOO.........OOOO.............
	.......O.O.O.......OOOOO.............
	........O..O......OO...............OO
	........OOO........OO..............OO
	.........O...........................
	.....................................
	.....................................
	.....................................
	.....................................
	..O.......O..........................
	.....................................
	OOO.......OOO........................
	.OO.OO.OO.OO.........................
	..OOO...OOO..........................
	...O.....O...........................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	..OO.....OO..........................
	..OO.....OO..........................

:MWSS-to-G See 135-degree MWSS-to-G, 45-degree MWSS-to-G.

:MW volcano (p5) Found by Dean Hickerson in April 1992.

	......O......
	....O...O....
	.............
	...O.....O...
	.OOO.OOO.OOO.
	O...OO.OO...O
	O.OOO.O.OOOO.
	.O...........
	...O.O.O.OO.O
	..OO.OOO.O.OO
	...O.O..O....
	...O..OO.....
	..OO.........

:My Experience with B-heptominos in Oscillators An article by Dave Buckingham (October 1996) that describes his discovery of Herschel conduits, including sufficient (indeed ample) stable conduits to enable, for the first time, the construction of period n oscillators - and true period n guns - for every sufficiently large integer n. (See Herschel loop and emu.)

:natural Occurring often in random patterns. There is no precise measure of naturalness, since the most useful definition of "random" in this context is open to debate. Nonetheless, it is clear that objects such as blocks, blinkers, beehives and gliders are very natural, while eater2s, darts, guns, etc., are not.

:negative spaceship A type of signal traveling through a periodic agar such as zebra stripes. The leading edge of the signal removes the agar, and the trailing edge rebuilds the agar some time later. The distance between the two edges is sometimes adjustable -- see lightspeed bubble. The central part of the "spaceship" may consist of dying sparks or even simple empty space.

Below is a sample period-5 negative spaceship, found by Hartmut Holzwart in March 2007, in a small stabilized section of zebra stripes agar:

	.O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O.
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.........................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOO..OOO..OOOOOOOOOOOOOOOOOOO.
	O..............................OO...OO..................O
	.OOOOOOOOOOOOOOOOOOOOOOOO..OOO...OO...OOOO..OOOOOOOOOOOO.
	..........................OO...............OO............
	.OOOOOOOOOOOOOOOOOOOOOOOO..OOO...OO.....OO...OO..OOOOOOO.
	O..............................OO...O.OO........OO......O
	.OOOOOOOOOOOOOOOOOOOOOOOO..OOO..OOO...OO.....OO...OOOOOO.
	..........................OO............OO.OO............
	.OOOOOOOOOOOOOOOOOOOOOOOO...OOOOO..........OO.....OOOOOO.
	O............................O...............OO.OO......O
	.OOOOOOOOOOOOOOOOOOOOOOOO.....O.........O.......OO..OOOO.
	..........................O.O......O...O..........OO.....
	.OOOOOOOOOOOOOOOOOOOOOOOO...O.O.OOOOO......O.......OOOOO.
	O..............................OOO...O......O...........O
	.OOOOOOOOOOOOOOOOOOOOOOOO...O.O.OOOOO......O.......OOOOO.
	..........................O.O......O...O..........OO.....
	.OOOOOOOOOOOOOOOOOOOOOOOO.....O.........O.......OO..OOOO.
	O............................O...............OO.OO......O
	.OOOOOOOOOOOOOOOOOOOOOOOO...OOOOO..........OO.....OOOOOO.
	..........................OO............OO.OO............
	.OOOOOOOOOOOOOOOOOOOOOOOO..OOO..OOO...OO.....OO...OOOOOO.
	O..............................OO...O.OO........OO......O
	.OOOOOOOOOOOOOOOOOOOOOOOO..OOO...OO.....OO...OO..OOOOOOO.
	..........................OO...............OO............
	.OOOOOOOOOOOOOOOOOOOOOOOO..OOO...OO...OOOO..OOOOOOOOOOOO.
	O..............................OO...OO..................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOO..OOO..OOOOOOOOOOOOOOOOOOO.
	.........................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O.
The "spaceship" travels to the left at the speed of light, so it will eventually reach the edge of any finite patch and destroy itself and its supporting agar.

:negentropy (p2) Compare Hertz oscillator.

	...OO.O....
	...O.OO....
	...........
	....OOO....
	...O.O.O.OO
	...OO..O.OO
	OO.O...O...
	OO.O...O...
	....OOO....
	...........
	....OO.O...
	....O.OO...

:neighbour Any of the eight cells adjacent to a given cell. A cell is therefore not considered to be a neighbour of itself, although the neighbourhood used in Life does in fact include this cell (see cellular automaton).

:new five (p3) Found by Dean Hickerson, January 1990.

	..OO.....
	.O..O....
	.O.O..O..
	OO.O.OO..
	O........
	.OOO.OOOO
	.....O..O
	O.OO.....
	OO.OO....

:new gun An old name for the second known basic gun (found, like the first, by Bill Gosper), shown below. A number of other ways of constructing a gun from two twin bees shuttles have since been found - see edge shooter for one of these.

	.........................OO.....OO
	.........................OO.....OO
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	..................................
	...........................OO.OO..
	..........................O.....O.
	..................................
	.........................O.......O
	.........................O..O.O..O
	.........................OOO...OOO
	..................................
	..................................
	..................................
	..................................
	.................O................
	OO...............OO...............
	OO................OO..............
	.............OO..OO...............
	..................................
	..................................
	..................................
	.............OO..OO...............
	OO................OO.......OO.....
	OO...............OO........OO.....
	.................O................

:Noah's ark The following diagonal puffer consisting of two switch engines. This was found by Charles Corderman in 1971. The name comes from the variety of objects it leaves behind: blocks, blinkers, beehives, loaves, gliders, ships, boats, long boats, beacons and block on tables.

	..........O.O..
	.........O.....
	..........O..O.
	............OOO
	...............
	...............
	...............
	...............
	...............
	.O.............
	O.O............
	...............
	O..O...........
	..OO...........
	...O...........

See also ark.

:n-omino Any polyomino with exactly n cells.

:nonfiller = space nonfiller

:non-monotonic A spaceship is said to be non-monotonic if its leading edge falls back in some generations. The first example (shown below) was found by Hartmut Holzwart in August 1992. This is p4 and travels at c/4. In April 1994, Holzwart found examples of p3 spaceships with this property, and this is clearly the smallest possible period. Another non-monotonic spaceship is the weekender.

	..........OO.O.......
	......OOO.O.OOO......
	..O.O..........O...OO
	OO....OO.....O...OOOO
	..O.OO..O....OOO.O...
	........O....O.......
	..O.OO..O....OOO.O...
	OO....OO.....O...OOOO
	..O.O..........O...OO
	......OOO.O.OOO......
	..........OO.O.......

:non-spark Something that looks like a spark, but isn't. An OWSS produces one of these instead of a belly spark, and is destroyed by it.

:non-standard spaceship Any spaceship other than a glider, LWSS, MWSS or HWSS.

:non-trivial A non-trivial period-N oscillator contains at least one cell oscillates at the full period. In other words, it is not made up solely of separate oscillators with smaller periods; it includes a spark or other reaction that would not occur if all lower-period subpatterns were separated from each other. See omniperiodic.

:NW31 One of the most common stable edge shooters. This Herschel-to-glider converter suppresses the junk ordinarily left behind by an evolving Herschel while allowing both the first natural glider and second natural glider to escape on transparent lanes:

	.......OO.......................
	........O.......................
	........O.O.....................
	.........OO.....................
	................................
	................................
	................................
	..............................OO
	..............................OO
	................................
	.........O......................
	.........O.O....................
	.........OOO....................
	...........O....................
	................................
	................................
	................................
	................................
	..OO............................
	...O............................
	OOO.............................
	O...............................
	....................OO..........
	....................OO..........

:NW31T120 The full designator of NW31. The T120 timing measurement means that a canonical NW glider placed at time T=120, at (+31, +0) relative to the input Herschel, would reach the exact same spacetime locations as the converter's output glider (assuming no interference from the conversion circuitry).

:oblique Neither diagonal nor orthogonal. See also knightship.

:obo spark A spark of the form O.O (so called after its rle encoding).

:octagon II (p5) The first known p5 oscillator, discovered in 1971 independently by Sol Goodman and Arthur Taber. The name is due to the latter.

	...OO...
	..O..O..
	.O....O.
	O......O
	O......O
	.O....O.
	..O..O..
	...OO...

:octagon IV (p4) Found by Robert Wainwright, January 1979.

	.......OO.......
	.......OO.......
	................
	......OOOO......
	.....O....O.....
	....O......O....
	...O........O...
	OO.O........O.OO
	OO.O........O.OO
	...O........O...
	....O......O....
	.....O....O.....
	......OOOO......
	................
	.......OO.......
	.......OO.......

:octomino Any 8-cell polyomino. There are 369 such objects. The word is particularly applied to the following octomino (or its two-generation successor), which is fairly common but lacks a proper name:

	..OO
	..OO
	OOO.
	.O..

:odd keys (p3) Found by Dean Hickerson, August 1989. See also short keys and bent keys.

	..........O.
	.O.......O.O
	O.OOO..OO.O.
	.O..O..O....
	....O..O....

:omino = polyomino

:omniperiodic A cellular automaton is said to be omniperiodic if it has oscillators of all periods. It is not known if Life is omniperiodic, although this seems likely. Dave Buckingham's work on Herschel conduits in 1996 (see My Experience with B-heptominos in Oscillators) left only a finite number of unresolved cases, further reduced by Noam Elkies between 1999 and 2002. At the time of writing (August 2017) no oscillators are known for periods 19, 23, 38, or 41. If we insist that the oscillator must contain a cell oscillating at the full period, then 34 should be added to this list. Period 43 and 53 oscillators were made possible in 2013 by Mike Playle's Snark.

Note that if we were to allow infinite oscillators, then all periods are certainly possible, as any period of 14 or more can be obtained using a glider (or LWSS) stream, or an infinitely long 2c/3 wire containing signals with the desired separation.

:one per generation See grow-by-one object.

:one-sided spaceship synthesis A glider synthesis of a spaceship in which all gliders come from the same side of the spaceship's path. Such syntheses are used extensively in the 17c/45 Caterpillar.

:one-time A concept used for turners and splitters, specifying that the reaction in question is not repeatable as it would be in a reflector or fanout device. Instead, the constellation is used up in the course of the reaction, usually leaving nothing behind.

:onion rings For each integer n>1 onion rings of order n is a stable agar of density 1/2 obtained by tiling the plane with a certain 4n × 4n pattern. The tile for order 3 onion rings is shown below - the reader should then be able to deduce the form of tiles of other orders.

	......OOOOOO
	.OOOO.O....O
	.O..O.O.OO.O
	.O..O.O.OO.O
	.OOOO.O....O
	......OOOOOO
	OOOOOO......
	O....O.OOOO.
	O.OO.O.O..O.
	O.OO.O.O..O.
	O....O.OOOO.
	OOOOOO......

:Online Life-Like CA Soup Search = The Online Life-Like CA Soup Search.

:on-off Any p2 oscillator in which all rotor cells die from overpopulation. The simplest example is a beacon. Compare flip-flop.

:O-pentomino Conway's name for the following pentomino, a traffic light predecessor, although not one of the more common ones.

	OOOOO

:orbit A term proposed by Jason Summers to refer to a natural stabilization of a puffer. For example, the switch engine has two (known) orbits, the block-laying one and the glider-producing one.

:Orion (c/4 diagonally, p4) Found by Hartmut Holzwart, April 1993.

	...OO.........
	...O.O........
	...O..........
	OO.O..........
	O....O........
	O.OO......OOO.
	.....OOO....OO
	......OOO.O.O.
	.............O
	......O.O.....
	.....OO.O.....
	......O.......
	....OO.O......
	.......O......
	.....OO.......
In May 1999, Jason Summers found the following smaller variant:
	.OO..........
	OO...........
	..O..........
	....O....OOO.
	....OOO....OO
	.....OOO.O.O.
	............O
	.....O.O.....
	....OO.O.....
	.....O.......
	...OO.O......
	......O......
	....OO.......

:orphan Conway's preferred term for a Garden of Eden. According to some definitions, a orphan consists of just the minimum living and dead cells needed to ensure that no parent is possible -- whereas a GoE is an entire infinite Life plane that contains an orphan.

:Orthogonoid (256c/3476016, p3476016) A self-constructing spaceship with a slow orthogonal direction of travel, analogous to the Demonoids but using MWSSes instead of gliders in the construction recipe. The first example was completed by Dave Greene on 29 June 2017.

:oscillator Any pattern that is a predecessor of itself. The term is usually restricted to non-stable finite patterns. An oscillator is divided into a rotor and a stator. See also omniperiodic.

In general cellular automaton theory the term "oscillator" usually covers spaceships as well, but this usage is not normal in Life.

:Osqrtlogt (p1 circuitry) A pattern constructed by Adam P. Goucher in 2010, which uses an unbounded triangular region as memory for a binary counter. Empty space is read as a zero, and a boat is a 1. The pattern's diametric growth rate is O(sqrt(log(t))), which is the slowest possible for any Life pattern, or indeed any 2D Euclidean cellular automaton. Since the population returns infinitely often to its initial minimum value (during carry operations from 11111...1 to 100000...0, it can be considered to be an unusual form of sawtooth.

:OTCA metapixel (p46 circuitry) A 2048 × 2048 period 35328 metacell constructed by Brice Due in 2006. It contains a large "pixel" area that contains a large population of LWSS spaceships when the cell state is ON, but is empty when the cell state is OFF. This allows the state of the cell to be visible at high zoom levels, unlike all previous unit cells where the state was signaled by the presence or absence of a single glider in a specific location.

:overclocking A term used when a circuit can accept a signal at a specific period which it cannot accept at a higher period. A syringe is a simple example. A better example is a Silver reflector, where overclocking creates a situation where the circuit can process input gliders much faster than the normal repeat time of 497 ticks, but the stream of gliders has to be continuous. Any interruption of the stream will cause the destruction of the reflector.

Some staged recovery circuits also permit overclocking, and can function successfully at a rate faster than their recovery time. A Silver reflector has a recovery time of 497 ticks, but can be overclocked to reflect a period 250 glider stream, or any nearby period above 248, simply by removing a beehive after the first glider enters the reflector. However, a continuous stream of gliders is then required to maintain the circuit, with timing within a tightly bounded range.

:overcrowding = overpopulation

:over-exposure = underpopulation

:overpopulation Death of a cell caused by it having more than three neighbours. See also underpopulation.

:overweight spaceship = OWSS

:OWSS A would-be spaceship similar to LWSS, MWSS and HWSS but longer. On its own an OWSS is unstable, but it can be escorted by true spaceships to form a flotilla.

:Ox A 1976 novel by Piers Anthony which involves Life.

:p = period

:p1 Period 1, i.e., stable. In the context of logic circuitry, this tends to mean that a mechanism is constructed from Herschel conduits that contain only still lifes as catalysts.

:p15 bumper A periodic colour-preserving glider reflector with Karel's p15 providing the necessary spark. The minimum repeat time is 45 ticks. For an equivalent colour-changing periodic glider reflector see p15 reflector. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	............................O.O
	............................OO.
	.............................O.
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	.................O.............
	.................O.O...........
	.................OO............
	...............................
	...............OO..............
	.OO.OO.OO.....O..O.............
	.OO....OO......O.O.............
	.OO.OO.OO.......O..............
	...............................
	....OO..............OO.........
	..O....O............O..........
	.O......O............OOO.......
	O........O.............O.......
	O........O.....................
	O........O.....................
	.O......O......................
	..O....O.......................
	....OO.........................

:p15 reflector Noam Elkies' colour-changing glider reflector, with Karel's p15 providing the necessary domino spark. Compare to the colour-preserving Snark. Minimum repeat time is 30 ticks.

	........................O..
	........................O.O
	........................OO.
	...........................
	...........................
	...........................
	...........................
	.................O.........
	................O..........
	................OOO........
	...........................
	...OO....OO.........OO.....
	..O..O..O..O....OO..OO.....
	..OO......OO...O.O.........
	..OO......OO....O..........
	....OO..OO.................
	..................OO.......
	..................O........
	...................OOO.....
	.O..O.OO.O..O........O.....
	OO..O....O..OO.............
	.O..O.OO.O..O..............

:p16 Oscillating Picture constructed by Otis Arron Schmakel in December 2004.

.......OO.....OOO......OO.......OO.......OOO.........
......O..O.....OOO....O..O.....O..O.......OOO........
.......O.O.............O.O......O.O...O.........O....
.....OO.O............OO.O.....OO.O...O.O........O....
.....OOO.............OOO......OOO.....O.......OOO....
.....OO....O.....O...OO.......OO..............OO.....
..........O.O...O.O......OO.........OOOOO.....OO..OOO
..........O..O.O..O.................O....O......OOO..
.O..........O...O......O...O...........O..O.....OOO..
.O..O.......OO.OO......O....O..........OO.O..O.......
.O..O....................O.O.O......O.....O.O.O......
..O.O.....................O.O.O....O.O....O..O.....OO
..O.O......................O....O..O..O..OO.......O.O
....OO......................O...O...OO..........OOO..
....OO........O................................O...O.
..O.O........O.O.............OO..OO........O..O..OOO.
..O.O.........O.................O.O........OO.O......
.O..O............................O.........O..O..OOO.
.O..O.......OOOOO.....OOOOOO.OO................O...O.
.O.........O....O.....OOOOOO.OO.................OOO..
..........O..O...............OO.....OOO..OO.......O.O
.......O..O.OO........OO.....OO.....OO....O..O.....OO
......O.O.O.....O.....OO.....OO.....O.....O.O.O......
OO.....O..O....OO.....OO.....OO........OO.O..O.......
O.O.......OO..OOO.....OO...............O..O..........
..OOO.................OO.OOOOOO.....O....O.........O.
.O...O................OO.OOOOOO.....OOOOO.......O..O.
.OOO..O..O.........O............................O..O.
......O.OO........O.O.................O.........O.O..
.OOO..O..O........OO..OO.............O.O........O.O..
.O...O................................O........OO....
..OOO..........OO...O...O......................OO....
O.O.......OO..O..O..O....O......................O.O..
OO.....O..O....O.O....O.O.O.....................O.O..
......O.O.O.....O......O.O.O....................O..O.
.......O..O.OO..........O....O......OO.OO.......O..O.
..OOO.....O..O...........O...O......O...O..........O.
..OOO......O....O.................O..O.O..O..........
OOO..OO.....OOOOO.........OO......O.O...O.O..........
.....OO..............OO.......OO...O.....O....OO.....
....OOO.......O.....OOO......OOO.............OOO.....
....O........O.O...O.OO.....O.OO............O.OO.....
....O.........O...O.O......O.O.............O.O.......
........OOO.......O..O.....O..O....OOO.....O..O......
.........OOO.......OO.......OO......OOO.....OO.......

:p1 megacell (p1 circuitry) A metacell constructed by Adam P. Goucher in 2008, capable of being programmed to emulate any Moore neighborhood rule, including isotropic and anisotropic non-totalistic rules. It fits in a 32768 by 32768 bounding box, with the resulting metacell grid at 45 degrees to the underlying Life grid. Like the OTCA metapixel, it includes a large "pixel" area so that the state of the megacell can easily be seen even at extremely small-scale zoom levels.

:p1 telegraph (p1 circuitry) A variant of Jason Summers' telegraph pattern, constructed in 2010 by Adam P. Goucher using only stable circuitry. A single incoming glider produces the entire ten-part composite lightspeed signal that restores the beehive-chain lightspeed wire to its original position. The signal is detected at the other end of the telegraph and converted back into a single output signal. This simplification came at the cost of a much slower transmission speed, one bit per 91080 ticks. In this mechanism, sending the entire ten-part signal constitutes a '1' bit, and not sending the signal means '0'.

:p22 bumper A periodic colour-preserving glider reflector with a repeat time of 44 ticks. Unlike the p5 through p8 cases where Noam Elkies' domino-spark based reflectors are available, no small period-22 colour-changing reflector is known. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	............................O..
	............................O.O
	............................OO.
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	O..............................
	OOO..............O.............
	...O.............O.O...........
	..OO.............OO............
	...............................
	....OOO........OO..............
	...O...O......O..O.............
	........O......O.O.............
	........O.......O..............
	...OO...O......................
	.....OO.............OO.........
	....................O..........
	.....................OOO.......
	.......................O.......
	...............................
	...............................
	...OO..........................
	.O...OO........................
	.O.............................
	.O.............................
	..O...O........................
	...OOO.........................
	...............................
	......OO.......................
	......O........................
	.......OOO.....................
	.........O.....................

:p30 shuttle = queen bee shuttle

:p45 glider gun A true-period glider gun discovered by Matthias Merzenich in April 2010. By most measures this is the smallest known odd-period gun of any type, either true-period or pseudo-period:

	.................................................
	.................................................
	.........................OO......................
	.....O..O.OO.O..O........O.......................
	....OO..O....O..OO.....O.O.......................
	.....O..O.OO.O..O......OO........................
	.................................................
	.................................................
	.................................................
	.................................................
	.................................................
	.................O..O............................
	.............OO..O..O............................
	.............OO..O..O.......OO...................
	............................OO....OO...O..O...OO.
	..O...............................OOOOO....OOOOO.
	..OOO.............................OO...O..O...OO.
	.....O......................OOO..................
	....OO...........................................
	.................................................
	............................OOO..................
	...........OOO...................................
	...................................O.O...........
	....................................OO...........
	....O......OOO......................O............
	...OOO...........................................
	.................................................
	............OO...................................
	...OOO......OO.......O..O..OO....................
	.....................O..O..OO....................
	...O.O...............O..O........................
	...O.O...........................................
	.................................................
	...OOO..........................................O
	..............................................O.O
	...............................................OO
	...OOO...........OO......O..O.OO.O..O............
	....O...........O.O.....OO..O....O..OO...........
	................O........O..O.OO.O..O............
	...............OO................................
	.................................................
	.................................................

:p46 shuttle = twin bees shuttle

:p4 bumper A periodic colour-preserving glider reflector with a minimum repeat time of 36. Unlike the p5 through p8 cases where Noam Elkies' domino spark-based reflectors are available, no small period-4 colour-changing reflector is known. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	...........................O..
	...........................O.O
	...........................OO.
	..............................
	..............................
	..............................
	..............................
	..............................
	....OO........................
	...O....O.........O...........
	...O.O.O.OO.......O.O.........
	..OO.O...OO.......OO..........
	.O...OOO.O....................
	O..OO....O......OO............
	OOO..O.OOO.....O..O...........
	...OO...OO......O.O...........
	..O..O.OOO.......O............
	..OOO....O....................
	.....OOO.O...........OO.......
	..OO.O...OO..........O........
	...O.O.O.OO...........OOO.....
	...O....O...............O.....
	....OO........................

:p4 reflector The following glider reflector, discovered by Karel Suhajda in October 2012. Its minimum repeat time is 52 ticks. Unlike the pipsquirter-based reflectors it is a colour-preserving reflector, so it was made obsolete the following year by the discovery of the much smaller stable Snark, which uses the same initial bait reaction and so produces an output glider with the same timing. For a small periodic colour-preserving glider reflector, see p4 bumper.

	................................O.........................
	...............................O..........................
	...............................OOO.......O.O..............
	........................................O.OO..............
	......................................OOO.....O...........
	.....................................O...OOOOOOOO.........
	..................................O.O.O..O.......O........
	..............O...................OOOO.OO.OOOOOOO.O.......
	..............OOO..................OOO.....O.O..O.O..OO...
	.................O...................OOO.O.O...OO.O.O.O...
	................OO.............OOO..OO.OOOOO....O.O.O.....
	.............................O.O...OOO.OO.O..O.OOOO..O..OO
	...........................OO.....O....O..O..O...O....O..O
	...................O.......OO.O.O..O......O..O....OOOOOOO.
	..................O...........O.O..O..O..O.........O......
	..................OOO........O....O..O...........O...OO...
	............................O.OOOOOOO........OO.O.OOO.O...
	.............................O.........O.O....O.O.O.......
	...................OO..........OOOOOOOOO.OOO..O.O.........
	...................OO.......O...O.......O...O.O.O.........
	...........................O..O...OOOO..O..O.O.O..........
	.............................OO...O...O.O.O..O............
	.............................O.....OOO.O.O.OO..O..........
	........OO...............O...OOO.....O...O...OOO..........
	...OO..O..O..................O...OO..O..O.OO..............
	...O....O.O..................O...OOOO...O.O.OO............
	OO.O.....O................OOO...O......OO...O.O...........
	.O.O.OO....................OOO.....O..OO..O.O.O...........
	O..O..O........OO...........OOO..OOO.OOO..O.O.OO..........
	OO..O....O.....O.O..........O..O...O...O..O.O.............
	.....OOOOO.......O...........O.O..O.OO...OOOO.............
	................O..........O.O.O.OOO.OOO.O................
	.......O.........OOO......O.OO.O..OO......................
	......O.O..........O......O.....O......OO.O...............
	.......O...................OOOOO......O..OO...............
	.............................O........OO..................

:p54 shuttle (p54) A surprising variant of the twin bees shuttle found by Dave Buckingham in 1973. See also centinal.

	OO.........................OO
	.O.........................O.
	.O.O.......O.............O.O.
	..OO.....O..O.....O......OO..
	............O.....OO.........
	........O..........OO........
	........O...OO....OO.........
	.........OOOOO...............
	.............................
	.........OOOOO...............
	........O...OO....OO.........
	........O..........OO........
	............O.....OO.........
	..OO.....O..O.....O......OO..
	.O.O.......O.............O.O.
	.O.........................O.
	OO.........................OO

:p5 bumper A periodic colour-preserving glider reflector with a middleweight volcano producing the necessary spark. Minimum repeat time is 35 ticks. For an equivalent colour-changing periodic glider reflector see p5 reflector. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	............................O
	..........................OO.
	...........................OO
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	...OO..O..........O..........
	...O..O.O.........O.O........
	....O.O.O.........OO.........
	...OO.O.OO...................
	..O...OO..O.....OO...........
	.O..OO...OOO...O..O..........
	.O.O.OO..OOO....O.O..........
	..O.OO...OOO.....O...........
	......OO..O..................
	OOOOO.O.OO...........OO......
	O..O..O.O............O.......
	.....O..O.............OOO....
	......OO................O....

:p5 reflector A colour-changing glider reflector constructed by Noam Elkies in September 1998, by welding together two special-purpose period-5 sparkers. Minimum repeat time is 25 ticks. For colour-preserving glider reflectors see p5 bumper and the stable Snark reflector.

	..........................O..
	........................OO...
	.........................OO..
	.............................
	.............................
	........OO...................
	.....O..O.O........O.........
	....O.O.O.O.......O..........
	...O.O.O..OO......OOO........
	...O...O.O..O................
	OO.OO..O.O.O..........OO.....
	O.O....OOO..O.....OO..OO.....
	..O.OOO...OO.....O.O.........
	..O..O.....O......O..........
	...O...O.O..O............OO..
	....OOO.OO.OO.......OO....O..
	......O....O........OO..OOO..
	.......OOO.O.....OO.....OOO..
	..........O.OO...OO.....OO...
	.........O..O..OOO.O........O
	.........OO..OOO...........OO
	................O............
	.............OOOO.O..........
	............O..O...O.........
	............OO...O.OOO.......
	.............O.O..O...O......
	.............O.OO.O..OO......
	..............O..O...........
	...............OO............

:p6 bumper A periodic colour-preserving glider reflector with a unix providing the necessary spark. Minimum repeat time is 36 ticks. For an equivalent colour-changing periodic glider reflector see p6 reflector. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	.......................O..
	.......................O.O
	.......................OO.
	..........................
	..........................
	..........................
	..........................
	..........................
	..........................
	..............O...........
	..............O.O.........
	..............OO..........
	..........................
	............OO............
	.....OO....O..O...........
	.....OO.....O.O...........
	.............O............
	..........................
	.....OOO.........OO.......
	OO..O.OO.........O........
	OO..OO............OOO.....
	....OO..............O.....

:p6 pipsquirter (p6) A pipsquirter oscillator found by Noam Elkies in November 1997, used in various hasslers and the colour-changing p6 reflector.

	.....O.........
	.....O.........
	...............
	...O...O.......
	.OOO.O.OOO.....
	O...OO....O....
	O.OO..OO.O.O...
	.O..OO..OO.O...
	..OO..OO.O.O.OO
	....O..O.O.O.OO
	....OOOO.OO....
	........O......
	......O.O......
	......OO.......

:p6 reflector (p7) Noam Elkies' colour-changing glider reflector using the p6 pipsquirter, with a minimum repeat time of 24 ticks. For colour-preserving glider reflectors see p6 bumper and the stable Snark reflector.

	.......................O.
	......................O..
	......................OOO
	...OO....................
	...O.....................
	.....O...................
	....OOOO.........O.......
	...O....O.......O........
	...OOOOO.O......OOO......
	.OO....O.O...............
	O..O.....OO.........OO...
	OO.O.O.O..O.....OO..OO...
	...O..O.OOO....O.O.......
	...OO.O...O.....O........
	.....O.O.OO..............
	.....O.O.O........OO.....
	......O..O........O......
	.......OO..........OOO...
	.....................O...

:p6 shuttle (p6) The following oscillator found by Nicolay Beluchenko in February 2004.

	O.............
	OOO...........
	...O..........
	..OO..........
	..............
	......O.......
	.....OOOO.....
	......O..O....
	.......OOO....
	..............
	..........OO..
	..........O...
	...........OOO
	.............O
This is extensible in more than one way:
	O........................
	OOO......................
	...O.....................
	..OO.....................
	.........................
	......O..................
	.....OOOO................
	......O..O...............
	.......OOO...............
	.........................
	..........OOO............
	..........O..O...........
	...........OOOO..........
	.............O...........
	.........................
	.................O.......
	................OOO......
	.................O.O.....
	.................O.O.....
	..................OO.....
	.....................OO..
	.....................O.O.
	.......................O.
	.......................OO

:p72 quasi-shuttle (p72) The following oscillator, found by Jason Summers in August 2005. Although this looks at first sight like a shuttle, it isn't really.

	..............................O......
	.............................OO......
	............................O.OO.....
	.OOOO......................OOO..O....
	O....O.......................O.O.O...
	O...O.O.......................O.O.O..
	.O...O.O......OO...............O..OOO
	.......O.....O.O................OO.O.
	.......O.....O...................OO..
	....O..O.....OOO.................O...
	.....OO..............................
	.....................................
	.....OO..............................
	....O..O.....OOO.................O...
	.......O.....O...................OO..
	.......O.....O.O................OO.O.
	.O...O.O......OO...............O..OOO
	O...O.O.......................O.O.O..
	O....O.......................O.O.O...
	.OOOO......................OOO..O....
	............................O.OO.....
	.............................OO......
	..............................O......

:p7 bumper A periodic colour-preserving glider reflector with a p7 pipsquirter attached to provide the necessary spark. Minimum repeat time is 35 ticks. For an equivalent colour-changing periodic glider reflector see p7 reflector. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	............................O
	..........................OO.
	...........................OO
	.............................
	.............................
	.............................
	.............................
	.............................
	.............................
	..................O..........
	.......O..........O.O........
	......O.O.........OO.........
	......O.O....................
	....O.O.OO......OO...........
	...O.OO..O.....O..O..........
	...O...OOO......O.O..........
	.O.OOOO..O.......O...........
	O.O...O.OO...................
	O..OOOO.O............OO......
	.O.O..O.O............O.......
	OO.O.O.O.OO...........OOO....
	O..OOO.O..O.............O....
	..O...O.O....................
	...OO.O.OO...................
	....O........................
	..O.O.OOOO...................
	.O.OOOO..O...................
	.O.....O.....................
	..OOOOOO.O...................
	....O...O.O..................
	.......O..O..................
	........OO...................

:p7 pipsquirter A pipsquirter oscillator found by Noam Elkies in August 1999, used in various hasslers and the colour-changing p7 reflector.

	................O.....
	........O.......O.....
	.OO...OOO..O..........
	..O..O...OOO..O...O.OO
	..O.O.OO....OOO.O.OO.O
	OO..O.O.OOOO....O.....
	.O.OO........OOO.OOOO.
	.O....O.O.OO...O.O..O.
	OO.O.O.OO....O.O......
	.O.O......OOOO.O......
	.O..OOOOOO....O.......
	OO....O..O..O.........
	............OO........

A larger period-7 pipsquirter is used in cases where space is limited where the reflector should extend southward for as short a distance as possible:

	.....OO..................................
	......OOO................................
	....O....O...............................
	..OOOOOO.O.............................O.
	.O.....O.OO....OO.....................O..
	.O.OO.O....O..O.O.....................OOO
	..O...O.OO.O..O..........................
	....O.O..O.OO.O..........................
	...OO...O.....OO.........................
	..O..OO.O.OOOO..O...OO...................
	O..O...O.O...O.O...O.O..........O........
	OO.O...O..OO.O..OOOO..OO.......O.........
	.O.O.OO.O.O.O.O.O...OO..O......OOO.......
	O..OOO..O.....O....O..O.O................
	O.O...O.OO...OO....O.OO.OO.........OO....
	.O.OOOO..O..O.O....O.....O.....OO..OO....
	...O...O......OO...O..OOOO....O.O........
	...O.OO..O..O.O....O.....O.....O.........
	....O.O.OO...OO....O.OO.OO...............
	......O.O.....O....O..O.O........OO......
	......O.O...O.O.O...OO..O........O.......
	.......O...O.O..OOOO..OO..........OOO....
	...........O.O.O...O.O..............O....
	............OO.OO...OO...................

:p7 reflector Noam Elkies' colour-changing glider reflector using a p7 pipsquirter, with a minimum repeat time of 28 ticks. A high-clearance version is shown in p7 pipsquirter. For colour-preserving glider reflectors see p7 bumper and the stable Snark reflector.

	.......................O.
	......................O..
	......................OOO
	.........................
	.........................
	.........................
	.........................
	................O........
	......OO.......O.........
	......O.O......OOO.......
	........O................
	...O..O.OO.........OO....
	...OOOO..O.....OO..OO....
	.......OOO....O.O........
	...OOOO..O.....O.........
	..O...O.OO...............
	.O.OOOO.O........OO......
	.O.O..O.O........O.......
	OO.O.O.O.OO.......OOO....
	O..OOO.O..O.........O....
	..O...O.O................
	...OO.O.OO...............
	....O....................
	..O.O.OOOO...............
	.O.OOOO..O...............
	.O.....O.................
	..OOOOOO.O...............
	....O...O.O..............
	.......O..O..............
	........OO...............

:p8 bumper A periodic colour-preserving glider reflector with a blocker attached to provide the necessary spark. Minimum repeat time is 40 ticks. For an equivalent colour-changing periodic glider reflector see p8 reflector. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	....................O..
	....................O.O
	....................OO.
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	.......................
	..........O............
	..........O.O..........
	..........OO...........
	.......................
	........OO.............
	.OO....O..O............
	.OO.....O.O............
	.OO......O.............
	..O....................
	.O.O.........OO........
	OO.O.........O.........
	..............OOO......
	................O......
	.OO....................
	.OO....................

:p8 G-to-H A small periodic variant of a stable two-glider-to-Herschel component found by Paul Callahan in November 1998 and used in the Callahan G-to-H, Silver reflector and Silver G-to-H. Minimum repeat time is 192 ticks, though some lower periods such as 96 are possible via overclocking. Here a ghost Herschel marks the output signal location:

	....O.........O...................
	....OOO.....OOO...................
	.......O...O......................
	..O...OO...OO.....................
	...O..............................
	.OOO..............................
	..................................
	..................................
	..................................
	...............................O..
	...............................O..
	....................OO.........OOO
	....................OO...........O
	........OO........................
	.......O..O.......................
	..OO....OO........................
	.O.O..............................
	.O................................
	OO................................
	..........OO......................
	..........O.......................
	...........OOO....................
	.............O...........OO.......
	.....................OO..OO.......
	....................O.O...........
	.....................O............
	.................O................
	................O.O....OO.........
	...............O...O...O..........
	..............O...O.....OOO.......
	.............O...O........O.......
	............O...O.................
	.............O.O..................
	..............O...................

:p8 reflector A glider reflector constructed by Noam Elkies in September 1998, with a mnimum repeat time of 24 ticks. It is a constellation containing a figure-8, boat, eater1, and block. For colour-preserving glider reflectors see p8 bumper and the stable Snark reflector.

	................O.
	...............O..
	...............OOO
	..................
	..................
	..................
	..........O.......
	.........O........
	.........OOO......
	..................
	.............OO...
	.........OO..OO...
	........O.O.......
	.........O........
	.....O............
	....O.O....OO.....
	...O...O...O......
	..O...O.....OOO...
	.O...O........O...
	O...O.............
	.O.O..............
	..O...............

:p9 bumper A periodic colour-preserving glider reflector with a repeat time of 36. Unlike the p5 through p8 cases where Noam Elkies' domino spark-based reflectors are available, no small period-9 colour-changing reflector is known. A stable Snark reflector can be substituted for any bumper. This changes the timing of the output glider, which can be useful for rephasing periodic glider streams.

	........................O..
	........................O.O
	........................OO.
	...........................
	...........................
	...........................
	...........................
	...........................
	...........................
	...............O...........
	......OO.......O.O.........
	.....O.O.......OO..........
	.OO..O.....................
	.O.O.OO......OO............
	...O...O....O..O...........
	O..O.O.OO....O.O...........
	OOO..O.O......O............
	...OO.O....................
	..O..O..O.........OO.......
	...OOOOOO.........O........
	...................OOO.....
	.....OO..............O.....
	.....OO....................

:p9 reflector = p9 bumper.

:pair of bookends = bookends

:pair of tables = table on table

:paperclip (p1)

	..OO.
	.O..O
	.O.OO
	OO.O.
	O..O.
	.OO..

:parallel grey ship = with-the-grain grey ship

:Parallel HBK ((6,3)c/245912, p245912) A much smaller successor to the half-baked knightship, constructed by Chris Cain in September 2014. Several slow-salvo recipes are needed to support the multi-glider salvo seeds at the upstream end of the spaceship. "Parallel" means that these recipes are sent in parallel instead of one after the other, in series, as in the original HBK.

:Parallel HBK gun An armless constructor pattern that is programmed to build Parallel HBK oblique spaceships every 125906944 ticks. This gun was created by Chris Cain on 3 January 2015.

:parasite A self-sustaining reaction attached to the output of a rake or puffer, that damages or modifies the standard output. Compare tagalong. In 2009, while experimenting with novelty generating patterns in Golly, Mitchell Riley discovered parasites on glider streams from p20 and p8 backward rakes. In some cases, parasites can even "reproduce", as in the pattern below, though the number of copies is limited since they will eventually use up their host glider stream:

	......O.............O.........
	.....OOO...........OOO........
	...OO.OOO.........OOO.OO......
	....O..O.OO.....OO.O..O.......
	.OO.O....O.O...O.O....O.OO....
	.OO.O.O..O.OO.OO.O..O.O.OO....
	.O........O.O.O.O........O....
	OO.......OO.O.O.OO.......OO...
	............O.O...............
	.......OOO.O...O.OOO..........
	......OO...........OO.........
	......O.....O....OO..O........
	.....OO....OOO...OO..O........
	...........O.OO...OOO.........
	............OOO....O..........
	............OOO...............
	............OOO...............
	............OO................
	..............................
	...................O.O........
	....................OO........
	...............OO...O.........
	........OO......OO............
	.......OO......O..............
	.........O....................
	..............................
	..............................
	.................OO...........
	..........O......OOO..........
	.........OOO.O...OOO..........
	........OO.O.....OOO..........
	........OO......O.OO..........
	........OO......OOO....OO.....
	........OO.OO....O.....O......
	.........OO...........OO......
	..........OOO.O...O.OOO.......
	...............O.O............
	...OO.......OO.O.O.OO.......OO
	....O........O.O.O.O........O.
	....OO.O.O..O.OO.OO.O..O.O.OO.
	....OO.O....O.O...O.O....O.OO.
	.......O..O.OO.....OO.O..O....
	......OO.OOO.........OOO.OO...
	........OOO...........OOO.....
	.........O.............O......

:parent A pattern is said to be a parent of the pattern it gives rise to after one generation. Some patterns have infinitely many parents, but other have none at all (see Garden of Eden).

:parent cells The three cells that cause a new cell to be born.

:parity Even or odd, particularly as applied to the phase of an oscillator or spaceship. For example, in slow salvo constructions, the intermediate targets are frequently period 2, most often because they contain blinkers or traffic lights. A glider striking a P2 constellation will generally produce a different result depending on its parity. Period-4 intermediate targets are rare (or not used), so it doesn't matter if an incoming glider is in phase 1 or phase 3 -- i.e., only the even/odd parity is important.

:PD = pentadecathlon

:pedestle (p5)

	.....O.....
	....O.O....
	.O..OO.....
	.OOO.......
	.....OOO...
	...OO...O..
	..O....O..O
	.O.O.O.O.OO
	.O.O...O.O.
	OO.O.O.O.O.
	O..O....O..
	..O...OO...
	...OOO.....
	.......OOO.
	.....OO..O.
	....O.O....
	.....O.....

:penny lane (p4) Found by Dave Buckingham, 1972.

	...OO.....OO...
	...O.......O...
	OO.O.......O.OO
	OO.O.OOOOO.O.OO
	....O..O..O....
	.....OOOOO.....
	...............
	.......O.......
	......O.O......
	.......O.......

:pentadecathlon (p15) Found in 1970 by Conway while tracking the history of short rows of cells, 10 cells giving this object, which is the most natural oscillator of period greater than 3. In fact it is the fifth or sixth most common oscillator overall, being about as frequent as the clock, but much less frequent than the blinker, toad, beacon or pulsar.

	..O....O..
	OO.OOOO.OO
	..O....O..
The pentadecathlon is the only known oscillator which is a polyomino in more than one phase.

:pentant (p5) Found by Dave Buckingham, July 1976.

	OO........
	.O........
	.O.O......
	..OO....OO
	.........O
	.....OOOO.
	.....O....
	..O...OOO.
	..OOOO..O.
	.....O....
	....O.....
	....OO....

:pentaplet Any 5-cell polyplet.

:pentapole (p2) The barberpole of length 5.

	OO......
	O.O.....
	........
	..O.O...
	........
	....O.O.
	.......O
	......OO

:pentoad (p5) Found by Bill Gosper, June 1977. This is extensible: if an eater is moved back four spaces then another Z-hexomino can can be inserted. (This extensibility was discovered by Scott Kim.)

	...........OO
	...........O.
	.........O.O.
	.........OO..
	.....OO......
	......O......
	......O......
	......OO.....
	..OO.........
	.O.O.........
	.O...........
	OO...........

:pentomino Any 5-cell polyomino. There are 12 such patterns, and Conway assigned them all letters in the range O to Z, loosely based on their shapes. Only in the case of the R-pentomino has Conway's label remained in common use, but all of them can nonetheless be found in this lexicon.

:period The smallest number of generations it takes for an oscillator or spaceship to reappear in its original form. The term can also be used for a puffer, wick, fuse, superstring, stream of spaceships, factory or gun. In the last case there is a distinction between true period and pseudo period. There is also a somewhat different concept of period for wicktrailers.

:period doubler See period multiplier.

:period multiplier A commonly used term for a pulse divider. Dividing the number of signals in a regular stream by N necessarily multiplies the period by N. For Herschel signals, a number of small period doubler, tripler, and quadrupler mechanisms are known. The term "period multiplier" can be somewhat misleading, because most such circuits can accept input streams that are not strictly periodic.

:perpendicular grey ship = against-the-grain grey ship

:perturb To change the fate of an object by reacting it with other objects. Typically, the other objects are sparks from spaceships or oscillators, or are eaters or impacting spaceships. Perturbations are typically done to turn a dirty reaction into a clean one, or to change the products of a reaction. In many desirable cases the perturbing objects are not destroyed by the reaction, or else are easily replenished.

:perturbation = perturb.

:phase A representative generation of a periodic object such as an oscillator or spaceship. The number of phases is equal to the period of the object. The phases of an object usually repeat in the same cyclic sequence forever, although some perturbations can cause a phase change.

:phase change A perturbation of a periodic object that causes the object to skip ahead by one or more phases. If the perturbation is repeated indefinitely, this can effectively change the period of the object. An example of this, found by Dean Hickerson in November 1998, is shown below. In this example, the period of the oscillator would be 7 if the mold were removed, but the period is increased to 8 because of the repeated phase changes caused by the mold's spark.

	..........O....
	.........O.OO..
	..OO.........O.
	..O......O..O.O
	.......O...O..O
	OOOOOO.O....OO.
	O..............
	.OO.OO...OO....
	..O.O....O.O...
	..O.O......O...
	...O.......OO..

The following pattern demonstrates a p4 c/2 spaceship found by Jason Summers, in which the phase is changed as it deletes a forward glider. This phase change allows the spaceship to be used to delete a glider wave produced by a rake whose period is 2 (mod 4).

	........O...........................
	.......OOO.OO.......................
	......OO...O.OO.....................
	.....OO..O.....O....................
	......O.....O...O.OOO...............
	.....OO.....O...O.O..O..............
	...OO.O.OO....O.O.O...O.............
	....O.O..OO...........O.............
	.OO.O..O..O.........O...............
	.OO.O.....OO.........O.OOO..........
	.O.O.............OOO.O.O.OO.........
	OO.OO...........OO.O..O.O.O.........
	..............OO.O...OOO..OO.....OO.
	.............O...O......O........O.O
	............O.....O..OO.O.OO.....O..
	...........O..O.O......O.O..........
	...........O.....OO....OOO..........
	.............O..........O...........
	..........O.O...........O...........
	.........OO.O.OOO...................
	........O.O.O...O...................
	.......OO.O.........................
	......O...O.....OO..................
	....................................
	......OO.OO.........................

Phase changing reactions have enabled the construction of spaceships having periods that were otherwise unknown, and also allow the construction of period-doubling and period-tripling convoys to easily produce very high period rakes.

See also blinker puffer.

:phi The following common spark. The name comes from the shape in the generation after the one shown here.

	.OOO.
	O...O
	O...O
	.OOO.

:phi calculator (p1 circuitry) See pi calculator.

:phoenix Any pattern all of whose cells die in every generation, but which never dies as a whole. A spaceship cannot be a phoenix, and in fact every finite phoenix eventually evolves into an oscillator. The following 12-cell oscillator (found by the MIT group in December 1971) is the smallest known phoenix, and is sometimes called simply "the phoenix".

	....O...
	..O.O...
	......O.
	OO......
	......OO
	.O......
	...O.O..
	...O....
Every known phoenix oscillator has period 2. In January 2000, Stephen Silver showed that a period 3 oscillator cannot be a phoenix. The situation for higher periods is unknown.

:pi = pi-heptomino

:Pianola breeder A series of patterns by by Paul Tooke in 2010, based on a simplification and extension of the Gemini spaceship's construction mechanism. Tooke produced a number of slow-salvo-constructed patterns with superlinear growth, including a series of breeder patterns of previously unknown types. For some patterns, the Gemini's two construction arms were moved to a permanent stationary platform, using fourteen glider-loop channels instead of twelve.

Some of these breeder patterns remain difficult to classify unambiguously. For example, one pattern was designed to be an MSS breeder -- a modified Gemini spaceship puffing slide guns which build lines of blocks. However, the slide guns produce both moving and stationary objects at a linear rate, because streams of gliders are needed to reach out to the construction zone to do the push reaction and build more blocks. The pattern could therefore be classified as a hybrid MSM/MSS breeder. Other breeder patterns utilizing slide guns and universal constructor technology are likely to cause similar classification ambiguities.

:pi calculator (p1 circuitry) A device constructed by Adam P. Goucher in February 2010, which calculates the decimal digits of pi (the transcendental number, not the Life pattern!) and displays them in the Life universe as 8×10 dot matrix characters formed by arrangements of blocks along a diagonal stripe at the top. A push reaction moves a ten-block diagonal cursor to the next position as part of the "printing" operation for each new digit.

The actual calculation is done in binary, using a streaming spigot algorithm based on linear fractional transformations. The pi calculator is made up of a 188-state computer connected to a printing device via period-8 regulators and a binary-to-decimal conversion mechanism. The complete pattern can be found in Golly's Very Large Patterns online archive, along with the very similar 177-state phi calculator which uses a simpler algorithm to calculate and print the Golden Ratio.

:pi climber The reaction that defines rate of travel of the Caterpillar spaceship. A pi climber consists of a pi-heptomino "climbing" a chain of blinkers, moving 17 cells every 45 ticks, and leaving behind an identical chain of blinkers, shifted downward by 6 cells. A single pi climber does not produce any gliders or other output, but two or more of them traveling on nearby blinker chains can be arranged to emit gliders every 45 ticks. Compare Herschel-pair climber.

	..O..
	..O..
	..O..
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	.....
	..O..
	.OOO.
	.O.O.

:pi-heptomino (stabilizes at time 173) A common pattern. The name is also applied to later generations of this object - in a pi ship, for example, the pi-heptomino itself never arises.

	OOO
	O.O
	O.O

:pincers = great on-off

:pinwheel (p4) Found by Simon Norton, April 1970. Compare clock II.

	......OO....
	......OO....
	............
	....OOOO....
	OO.O....O...
	OO.O..O.O...
	...O...OO.OO
	...O.O..O.OO
	....OOOO....
	............
	....OO......
	....OO......

:pi orbital (p168) Found by Noam Elkies, August 1995. In this oscillator, a pi-heptomino is turned ninety degrees every 42 generations. A second pi can be inserted to reduce the period to 84.

	..............OO....OO....OO...............................
	.............O..O.O....O.O..O..............................
	.............OOO..........OOO..............................
	................OO......OO.................................
	...............O..OOOOOO..O................................
	...............OO........OO................................
	...........................................................
	........O.............................OO..........O........
	.......O...OOO......O.........O.......OO.........O.O.......
	........O.OOOOO..........OOO...O...........................
	............O...O.....O.OOOOO.O..................O.........
	............OO....OOO.....O......................OO........
	............OO....OOO....OO...................OOOOO........
	...................O.....OO...................OO.OO.....OO.
	.................................................O......O.O
	.....................................................OO.O.O
	.....................................................O.O.O.
	.......................................................O...
	...................................OOO.........O.O...O..O..
	.......OO..........................O..O........O..O.....O..
	.......OO..............................O.......O.O..O...O..
	...................................O..O.............O...O..
	...................................OOO..................O..
	.....................................................O..O..
	................................................O......O...
	.............................................OO.OO...O.O.O.
	.............................................OOOOO...OO.O.O
	.........O......................................OO......O.O
	........O.O.....................................O.......OO.
	...........................................................
	.OO.......O.....................................O.O........
	O.O......OO......................................O.........
	O.O.OO...OOOOO.............................................
	.O.O.O...OO.OO.............................................
	...O......O................................................
	..O..O.....................................................
	..O........................................................
	..O...O....................................................
	..O...O..O.O......................................OO.......
	..O.....O..O......................................OO.......
	..O..O...O.O...............................................
	...O.......................................................
	.O.O.O.....................................................
	O.O.OO.....................................................
	O.O......O.................................................
	.OO.....OO.OO...................OO.....O...................
	........OOOOO...................OO....OOO....OO............
	........OO......................O.....OOO....OO............
	.........O..................O.OOOOO.O.....O...O............
	...........................O...OOO..........OOOOO.O........
	.......O.O.........OO.......O.........O......OOO...O.......
	........O..........OO.............................O........
	...........................................................
	................................OO........OO...............
	................................O..OOOOOO..O...............
	.................................OO......OO................
	..............................OOO..........OOO.............
	..............................O..O.O....O.O..O.............
	...............................OO....OO....OO..............

:pi portraitor (p32) Found by Robert Wainwright in 1984 or 1985. Compare with gourmet and popover.

	...........OO...........
	......OO.O....O.OO......
	......O..........O......
	.......OO......OO.......
	....OOO..OOOOOO..OOO....
	....O..O........O..O....
	.OO.O.O..........O.O.OO.
	.O.O.O............O.O.O.
	...O................O...
	.O..O..............O..O.
	....O.......OOO....O....
	O...O.......O.O....O...O
	O...O.......O.O....O...O
	....O..............O....
	.O..O..............O..O.
	...O................O...
	.O.O.O............O.O.O.
	.OO.O.O..........O.O.OO.
	....O..O........O..O....
	....OOO..OOOOOO..OOO....
	.......OO......OO.......
	......O..........O......
	......OO.O....O.OO......
	...........OO...........

:pipsquirt = pipsquirter

:pipsquirter An oscillator that produces a domino spark that is orientated parallel to the direction from which it is produced (in contrast to domino sparkers like the pentadecathlon and HWSS, which produce domino sparks perpendicular to the direction of production). See p6 pipsquirter, p7 pipsquirter.

:pi ship A growing spaceship in which the back part consists of a pi-heptomino travelling at a speed of 3c/10. The first example was constructed by David Bell. All known pi ships are too large to show here, but the following diagram shows how the pi fuse works.

	............O............
	...........O.O...........
	OO........OO.OO........OO
	OO.....................OO

:piston (p2) Found in 1971.

	OO.......OO
	O.O..O..O.O
	..OOOO..O..
	O.O..O..O.O
	OO.......OO

:pi wave A line of pi-heptominoes stabilizing one another. For example, an infinite line of pi-heptominoes arranged as shown below produces a pi wave that moves at a speed of 3c/10, and leaves no debris.

	OOO...............OOO...............OOO...............OOO
	O.O...............O.O...............O.O...............O.O
	O.O...............O.O...............O.O...............O.O

:pixel = cell

:plet = polyplet

:polyomino A finite collection of orthogonally connected cells. The mathematical study of polyominoes was initiated by Solomon Golomb in 1953. Conway's early investigations of Life and other cellular automata involved tracking the histories of small polyominoes, this being a reasonable way to ascertain the typical behaviour of different cellular automata when the patterns had to be evolved by hand rather than by computer. Polyominoes have no special significance in Life, but their extensive study during the early years lead to a number of important discoveries and has influenced the terminology of Life. (Note on spelling: As with "dominoes" the plural may also be spelt without an e. In this lexicon I have followed Golomb in using the longer form.)

It is possible for a polyomino to be an oscillator. In fact there are infinitely many examples of such polyominoes, namely the cross and its larger analogues. The only other known examples are the block, the blinker, the toad, the star and (in two different phases) the pentadecathlon.

A polyomino can also be a spaceship, as the LWSS, MWSS and HWSS show.

:polyplet A finite collection of orthogonally or diagonally connected cells. This king-wise connectivity is a more natural concept in Life than the orthogonal connectivity of the polyomino.

:pond (p1)

	.OO.
	O..O
	O..O
	.OO.

:pond on pond (p1) This term is often used to mean bi-pond, but may also be used of the following pseudo still life.

	.OO...OO.
	O..O.O..O
	O..O.O..O
	.OO...OO.

:popover (p32) Found by Robert Wainwright in August 1984. Compare with gourmet and pi portraitor.

	.....................O..........
	.....................O..........
	.....................OOO........
	.............OO.......OO........
	.............OO..OOO..OO........
	...................OOO..........
	...................OOO..........
	..............OO................
	..OOO........O..O...............
	..OOO........O.O................
	OOO..OO...O...O....OOO..........
	.....OO...O.....................
	....OOO...O.....................
	....O.................OO...OO...
	....O...........OOO..O..O..OO...
	........O.......O.O...O.O.......
	.......O.O......O.O....O........
	...OO..O..O................O....
	...OO...OO.................O....
	.....................O...OOO....
	.....................O...OO.....
	..........OOO........O...OO..OOO
	.................OO........OOO..
	................O..O.......OOO..
	................O.O.............
	..........OOO....O..............
	..........OOO...................
	........OO..OOO..OO.............
	........OO.......OO.............
	........OOO.....................
	..........O.....................
	..........O.....................

:population The number of ON cells.

:P-pentomino Conway's name for the following pentomino, a common spark.

	OO
	OO
	O.

:PPS (c/5 orthogonally, p30) A pre-pulsar spaceship. Any of three different p30 c/5 orthogonal spaceships in which a pre-pulsar is pushed by a pair of spiders. The back sparks of the spaceship can be used to perturb gliders in many different ways, allowing the easy construction of c/5 puffers. The first PPS was found by David Bell in May 1998 based on a p15 pre-pulsar spaceship found by Noam Elkies in December 1997. See also SPPS and APPS.

:pre-beehive The following common parent of the beehive.

	OOO
	OOO

:pre-block The following common parent of the block. Another such pattern is the grin.

	O.
	OO

:precursor = predecessor

:predecessor Any pattern that evolves into a given pattern after one or more generations.

:pre-pulsar A common predecessor of the pulsar, such as that shown below. This duplicates itself in 15 generations. (It fails, however, to be a true replicator because of the way the two copies then interact.)

	OOO...OOO
	O.O...O.O
	OOO...OOO

A pair of tubs can be placed to eat half the pre-pulsar as it replicates; this gives the p30 oscillator Eureka where the pre-pulsar's replication becomes a movement back and forth. (See twirling T-tetsons II for a variation on this idea.) By other means the replication of the pre-pulsar can be made to occur in just 14 generations as half of it is eaten; this allows the construction of p28 and p29 oscillators, and is in fact the only known method for creating a p29 oscillator. The pre-pulsar is also a vital component of the only known p47 oscillator.

See also PPS.

:pre-pulsar spaceship = PPS.

:pressure cooker (p3) Found by the MIT group in September 1971. Compare mini pressure cooker.

	.....O.....
	....O.O....
	....O.O....
	...OO.OO...
	O.O.....O.O
	OO.O.O.O.OO
	...O...O...
	...O...O...
	....OOO....
	...........
	...O.OO....
	...OO.O....

:primer A pattern originally constructed by Dean Hickerson in November 1991 that emits a stream of LWSSs representing the prime numbers. Some improvements were found by Jason Summers in October 2005.

:PRNG = pseudo-random number generator

:protein (p3) Found by Dave Buckingham, November 1972.

	....OO.......
	....O........
	......O......
	..OOOO.O.OO..
	.O.....O.O..O
	.O..OO.O.O.OO
	OO.O.....O...
	...O..OO.O...
	...O....O....
	....OOOO.....
	.............
	....OO.......
	....OO.......

:pseudo Opposite of true. A gun emitting a period n stream of spaceships (or rakes) is said to be a pseudo period n gun if its mechanism oscillates with a period different from n. This period will necessarily be a multiple of n. Pseudo period n glider guns are known to exist for all periods greater than or equal to 14, with smaller periods being impossible. The first pseudo p14 gun was built by Dieter Leithner in 1995.

The same distinction between true and pseudo also exists for puffers.

:pseudo-barberpole (p5) Found by Achim Flammenkamp in August 1994. In terms of its minimum population of 15 this is the smallest known p5 oscillator.

	..........OO
	...........O
	.........O..
	.......O.O..
	............
	.....O.O....
	............
	...O.O......
	............
	..OO........
	O...........
	OO..........

:pseudo-random glider generator A pseudo-random number generator in which the bits are represented by the presence or absence of gliders. The first pseudo-random glider generator was built by Bill Gosper. David Bell built the first moving one in 1997, using c/3 rakes.

:pseudo-random number generator A pseudo-random number generator (PRNG) is an algorithm that produces a sequence of bits that looks random (but cannot really be random, being algorithmically determined).

In Life, the term refers to a PRNG implemented as a Life pattern, with the bits represented by the presence or absence of objects such as gliders or blocks. Such a PRNG usually contains gliders or other spaceships in a loop with a feedback mechanism that causes later spaceships to interfere with the generation of earlier spaceships. The period can be very high, as a loop of n spaceships has 2n possible states.

:pseudo still life The strict definition of still life rules out such stable patterns as the bi-block. In such patterns there are dead cells which have more than 3 neighbours in total, but fewer than 3 in any component still life. These patterns are called pseudo still lifes. Mark Niemiec and others have enumerated the pseudo still lifes up to 32 bits; these figures are shown below.

	--------------
	Bits    Number
	--------------
	 8           1
	 9           1
	10           7
	11          16
	12          55
	13         110
	14         279
	15         620
	16        1645
	17        4067
	18       10843
	19       27250
	20       70637
	21      179011
	22      462086
	23     1184882
	24     3068984
	25     7906676
	26    20463274
	27    52816265
	28   136655095
	29   353198379
	30   914075620
	31  2364815358
	32  6123084116
	--------------

:puffer An object that moves like a spaceship, except that it leaves debris behind. The first known puffers were found by Bill Gosper and travelled at c/2 orthogonally (see diagram below for the very first one, found in 1971). Not long afterwards c/12 diagonal puffers were found (see switch engine). Discounting wickstretchers (which are not puffers in the conventional sense), no new velocity was obtained after this until David Bell found the first c/3 orthogonal puffer in April 1996. Since then c/5 orthogonal puffers have also been found, the first by Tim Coe in May 1997. Jason Summers built the first c/4 orthogonal puffer in January 1999, and the first 2c/5 orthogonal puffer in February 1999. Hartmut Holzwart built the first c/4 diagonal puffer (as opposed to a wickstretcher) in February 2004.

	.OOO......O.....O......OOO.
	O..O.....OOO...OOO.....O..O
	...O....OO.O...O.OO....O...
	...O...................O...
	...O..O.............O..O...
	...O..OO...........OO..O...
	..O...OO...........OO...O..

:puffer engine A pattern which can be used as the main component of a puffer. The pattern may itself be a puffer (e.g. the classic puffer train), it may be a spaceship (e.g. the Schick engine), or it may even be unstable (e.g. the switch engine).

:pufferfish (c/2, p12) A puffer discovered by Richard Schank in November 2014, from a symmetric soup search using an early version of apgsearch. It consists of a pair of B-heptominoes stabilised by a backend that leaves only pairs of blocks behind. It is simple enough to be easily synthesized with gliders.

	...O.......O...
	..OOO.....OOO..
	.OO..O...O..OO.
	...OOO...OOO...
	...............
	....O.....O....
	..O..O...O..O..
	O.....O.O.....O
	OO....O.O....OO
	......O.O......
	...O.O...O.O...
	....O.....O....

:pufferfish spaceship (c/2, p36) Generally, any spaceship constructed using pufferfish. May refer specifically to the extensible c/2 spaceship constructed by Ivan Fomichev in December 2014, the first such spaceship to contain no period-2 or period-4 parts. (The first two or three rows might be considered to be period 2 or 4, but they are directly dependent on following rows for support.).

The pattern consists of two adjacent pufferfish spaceships, plus four copies of a nontrivial period 36 c/2 fuse for pufferfish exhaust, discovered using a randomized soup search.

	.......O.......O..................O.......O........
	......OOO.....OOO................OOO.....OOO.......
	.....O..OO...OO..O..............OO.O.....O.OO......
	.....O...O...O...O...............OO.O...O.OO.......
	......OO.OO.OO.OO..............O.OO.......OO.O.....
	......OO.O...O.OO.............O.O..O.O.O.O..O.O....
	........O.....O...............O.O...OO.OO...O.O....
	.........OO.OO.................OOO.O.....O.OOO.....
	....OO..O.....O..OO.............OOO.......OOO......
	....OO..O.....O..OO.............OO.........OO......
	................................O...........O......
	........O.O.O.O................OO...........OO.....
	........OO...OO................OO...........OO.....
	...................................................
	...................................OO...OO.........
	...................O..........O....OO...OO.........
	...O..............OOO........OOO..............O....
	..OOO...OO...O.O.OO.O.......OO.O.............OOO...
	.OO..O..OO.........O........OOO.............OO.O...
	.OOOO.O......O...O.O........OOO.............OO.....
	OO.....O.......OO..OO.......OOOO..............OO...
	.O................O..O......O..O...........O..OO...
	.O.OOO..O....O.O..OO.......OO..............O....O..
	.O.O...OO....O.O..OO...O....O.O...........O..O.O...
	.OO......O..O.......O..O....OOO..........OO...OO...
	O.....O.O....O.O....O.OO................O..........
	.OO..O..O....O......O.OO............O....OO........
	.OO...OO.......OO...OO.OO..OO......OOOOOO..........
	........................O....O....O.O.O.O.......OOO
	..............................O...O..O.........O...
	..............................O....O..........O....
	.............................O.................O.O.

:puffer train The full name for a puffer, coined by Conway before any examples were known. The term was also applied specifically to the classic puffer train found by Bill Gosper and shown below. This is very dirty, and the tail does not stabilize until generation 5533. It consists of a B-heptomino (shown here one generation before the standard form) escorted by two LWSS. (This was the second known puffer. The first is shown under puffer.)

	.OOO...........OOO
	O..O..........O..O
	...O....OOO......O
	...O....O..O.....O
	..O....O........O.
In April 2006, Jason Summers found a way to make the classic puffer train into a p20 spaceship by adding a glider at the back:
	OOO...........OOO.
	O..O..........O..O
	O......OOO....O...
	O.....O..O....O...
	.O.O..O...O....O.O
	.......OOOO.......
	.........O........
	..................
	..................
	..................
	.......OOO........
	.......O..........
	........O.........

:puff suppressor An attachment at the back of a line puffer that suppresses all or some of its puffing action. The example below (by Hartmut Holzwart) has a 3-cell puff suppressor at the back which suppresses the entire puff, making a p2 spaceship. If you delete this puff suppressor then you get a p60 double beehive puffer. Puff suppressors were first recognised by Alan Hensel in April 1994.

	............O....................
	..........OO.O...................
	..........OO...O.................
	........O...OO.O.....O...........
	........OOOO.OO...OOOO.......O.O.
	......O......O....OOO.....O.O..O.
	......OOOOOOO...O...O....O..O....
	...O.O......OO..O...O.O.OO....O..
	..OOOOOOOOO.....O..OO........O...
	.OO..............O.OO.OOOO...O..O
	OO....OO.O..........O...O..O.O...
	.OO....O........OOO......O.O.O..O
	.........O......OO......O....OO..
	.OO....O........OOO......O.O.O..O
	OO....OO.O..........O...O..O.O...
	.OO..............O.OO.OOOO...O..O
	..OOOOOOOOO.....O..OO........O...
	...O.O......OO..O...O.O.OO....O..
	......OOOOOOO...O...O....O..O....
	......O......O....OOO.....O.O..O.
	........OOOO.OO...OOOO.......O.O.
	........O...OO.O.....O...........
	..........OO...O.................
	..........OO.O...................
	............O....................

:pull A reaction, most often mediated by gliders, that moves an object closer to the source of the reaction. See block pull, blinker pull, loaf pull; also elbow.

:pulsar (p3) Despite its size, this is the fourth most common oscillator (and by far the most common of period greater than 2) and was found very early on by Conway. See also pre-pulsar and pulsar quadrant.

	..OOO...OOO..
	.............
	O....O.O....O
	O....O.O....O
	O....O.O....O
	..OOO...OOO..
	.............
	..OOO...OOO..
	O....O.O....O
	O....O.O....O
	O....O.O....O
	.............
	..OOO...OOO..

:pulsar 18-22-20 = two pulsar quadrants

:pulsar CP 48-56-72 = pulsar (The numbers refer to the populations of the three phases.)

        ..OOO...OOO..
        .............
        O....O.O....O
        O....O.O....O
        O....O.O....O
        ..OOO...OOO..
        .............
        ..OOO...OOO..
        O....O.O....O
        O....O.O....O
        O....O.O....O
        .............
        ..OOO...OOO..

:Pulsar Pixel Display (p30 circuitry) A large-scale raster line display device constructed by Mark Walsh in August 2010, where pulsars form the individual pixels in an otherwise empty grid. The published sample pattern displays and erases eight 7×5-pixel characters on each of two lines of text.

:pulsar quadrant (p3) This consists of a quarter of the outer part of a pulsar stabilized by a cis fuse with two tails. This is reminiscent of mold and jam. Found by Dave Buckingham in July 1973. See also two pulsar quadrants.

	.....O..
	...OOO..
	..O...OO
	O..O..O.
	O...O.O.
	O....O..
	........
	..OOO...

:pulse A moving object, such as a spaceship or Herschel, which can be used to transmit information. See pulse divider.

Also another name for a pulsar quadrant.

:pulse divider A mechanism that lets every n-th object that reaches it pass through, and deletes all the rest, where n > 1 and the objects are typically spaceships or Herschels. For n=2, the simplest known stable pulse divider is the semi-Snark.

The following diagram shows a p5 glider pulse divider by Dieter Leithner (February 1998). The first glider moves the centre block and is reflected at 90 degrees. The next glider to come along will not be reflected, but will move the block back to its original position. The relatively small size and low period of this example made it useful for constructing compact glider guns of certain periods, but it became largely obsolete with the discovery of the semi-Snark. p7, p22, p36 and p46 versions of this pulse divider are also known.

	.....OO...................
	.....OO...................
	..........................
	..................OO......
	.................O..O.....
	.................O.O..O..O
	O...............OO.O.OOOOO
	.OO...........O...OO......
	OO...............OO..OOO..
	.............O...O.O..O.O.
	........OO.......OO..OO.O.
	........OO....O...OO...O..
	................OO.O.OO...
	.................O.O.O....
	.................O.O..O...
	..................O..OO...
	..OO......................
	...O......................
	OOO.......................
	O.........................
	..........................
	............OO............
	............O.............
	.............OOO..........
	...............O..........

:pulshuttle V (p30) Found by Robert Wainwright, May 1985. Compare Eureka.

	.............O..............O.............
	............O.O.......O....O.O............
	.............O......OO.OO...O.............
	......................O...................
	..OO......OO..................OO......OO..
	O....O..O....O..............O....O..O....O
	O....O..O....O..............O....O..O....O
	O....O..O....O........O.....O....O..O....O
	..OO......OO........OO.OO.....OO......OO..
	......................O...................
	..........................................
	..........................................
	..OO......OO..................OO......OO..
	O....O..O....O........O.....O....O..O....O
	O....O..O....O......OO.OO...O....O..O....O
	O....O..O....O........O.....O....O..O....O
	..OO......OO..................OO......OO..
	..........................................
	..........................................
	......................O...................
	..OO......OO........OO.OO.....OO......OO..
	O....O..O....O........O.....O....O..O....O
	O....O..O....O..............O....O..O....O
	O....O..O....O..............O....O..O....O
	..OO......OO..................OO......OO..
	......................O...................
	.............O......OO.OO...O.............
	............O.O.......O....O.O............
	.............O..............O.............

:pure glider generator A pattern that evolves into one or more gliders, and nothing else. There was some interest in these early on, but they are no longer considered important. Here's a neat example:

	..O............
	..O............
	OOO............
	...............
	......OOO......
	.......O.......
	............OOO
	............O..
	............O..

:push A reaction that moves an object farther away from the source of the reaction. See sliding block memory, pi calculator, elbow, universal constructor. See also pull, fire.

:pushalong Any tagalong at the front of a spaceship. The following is an example (found by David Bell in 1992) attached to the front of a MWSS.

	..OOO.O.....
	.OOOO.O.....
	OO..........
	.O.O........
	..OOOO.O....
	...OOO......
	............
	............
	......OOOOO.
	......O....O
	......O.....
	.......O...O
	.........O..

:pyrotechnecium (p8) Found by Dave Buckingham in 1972.

	.......O........
	.....OOOOO......
	....O.....O.....
	.O..O.O.OO.O....
	O.O.O.O....O..O.
	.O..O....O.O.O.O
	....O.OO.O.O..O.
	.....O.....O....
	......OOOOO.....
	........O.......

:pyrotechneczum A common mistaken spelling of pyrotechnecium, caused by a copying error in the early 1990s.

:python = long snake

:Q = Quetzal

:qd Abbreviation for quarter diagonal.

:Q-pentomino Conway's name for the following pentomino, a traffic light predecessor.

	OOOO
	...O

:quad (p2) Found by Robert Kraus, April 1971. Of all oscillators that fit in a 6×6 box this is the only flipper.

	OO..OO
	O..O.O
	.O....
	....O.
	O.O..O
	OO..OO

:QuadLife A form of colourised Life in which there are four types of ON cell. A newly-born cell takes the type of the majority of its three parent cells, or the remaining type if its parent cells are all of different types. In areas where there are only two types of ON cell QuadLife reduces to Immigration.

:quadpole (p2) The barberpole of length 4.

	OO.....
	O.O....
	.......
	..O.O..
	.......
	....O.O
	.....OO

:quadratic filter A toolkit developed by Dean Hickerson and Gabriel Nivasch in 2006, enabling the construction of patterns with asymptotic population growth matching an infinite number of different sublinear functions -- namely, O(t(1/2n)) for any chosen n. See also exponential filter, recursive filter.

:quadratic growth The fastest possible asymptotic rate of population growth for any Life pattern -- O(t2) in big-O notation, where t is the number of ticks. The first quadratic-growth pattern found was Bill Gosper's breeder, in 1971; many other types of breeders and spacefillers have been constructed since.

In April 2011, Stephen Silver gave an example of a one-cell-thick pattern over a million cells long that exhibited quadratic growth. In November 2014, Chris Cain constructed a one-cell-thick pattern with a reduced bounding box of 7242×1.

There are an infinite number of possible growth rates for Life patterns, between linear and quadratic growth -- see superlinear growth.

:quadratic replicator A pattern that fills all or part of the Life plane by making copies of itself in a nonlinear way. Small quadratic replicators are known in other Life-like rules, but as of January 2016 no example has been found or constructed in Conway's Life.

:quadratic sawtooth Any sawtooth pattern with a quadratic envelope, or specifically a pattern assembled by Martin Grant in May 2015, consisting of two caber tossers with period multipliers for timing which activate and deactivate two toggle rake guns. The gliders emitted by those rakes annihilate on the diagonal while the rakes are eaten by 2c/5 ships. All the rakes and gliders are destroyed before the next cycle. See also Osqrtlogt.

:quapole = quadpole

:quarter (c/4 diagonally, p4) The following spaceship, found by Jason Summers in September 2000. The name is due to the 25-cell minimum population. This is the smallest known c/4 spaceship other than the glider. This spaceship can also be used to make the smallest known tubstretcher.

	........OO...
	.......OO....
	.........O...
	...........OO
	..........O..
	.............
	.........O..O
	.OO.....OO...
	OO.....O.....
	..O....O.O...
	....OO..O....
	....OO.......

:quarter diagonal A unit of measurement sometimes used for diagonal distances, especially for slow salvo glider lanes. One advantage of measurement in quarter diagonals is that gliders travel diagonally at 1qd/tick, so that the same integer value can serve as either a time or a diagonal distance measurement.

:quasar (p3) Found by Robert Wainwright, August 1971. See pulsar.

	..........OOO...OOO..........
	.............................
	........O....O.O....O........
	........O....O.O....O........
	........O....O.O....O........
	..........OOO...OOO..........
	.............................
	........OOO.......OOO........
	..OOO..O....O...O....O..OOO..
	.......O....O...O....O.......
	O....O.O....O...O....O.O....O
	O....O.................O....O
	O....O..OOO.......OOO..O....O
	..OOO...................OOO..
	.............................
	..OOO...................OOO..
	O....O..OOO.......OOO..O....O
	O....O.................O....O
	O....O.O....O...O....O.O....O
	.......O....O...O....O.......
	..OOO..O....O...O....O..OOO..
	........OOO.......OOO........
	.............................
	..........OOO...OOO..........
	........O....O.O....O........
	........O....O.O....O........
	........O....O.O....O........
	.............................
	..........OOO...OOO..........

:queen bee See queen bee shuttle.

:queen bee shuttle (p30) Found by Bill Gosper in 1970. There are a number of ways to stabilize the ends. Gosper originally stabilized shuttles against one another in a square of eight shuttles. Two simpler methods are shown here; for a third see buckaroo. The queen bee shuttle is the basis of all known true p30 guns (see Gosper glider gun).

	.........O............
	.......O.O............
	......O.O.............
	OO...O..O.............
	OO....O.O.............
	.......O.O........OO..
	.........O........O.O.
	....................O.
	....................OO

:Quetzal Dieter Leithner's name for the true p54 glider gun he built in January 1998. (This is short for Quetzalcoatlus and expresses the fact that the gun was a very large Herschel loop that was not an emu.) Shortly afterwards Leithner also built a p56 Quetzal using a mechanism found by Noam Elkies for this purpose. In October 1998 Stephen Silver constructed a p55 Quetzal using Elkies' p5 reflector of the previous month.

Some of the more recent Quetzals are not Herschel loops, but are instead short Herschel tracks firing several glider streams all but one of which is reflected back to the beginning of the track to create a new Herschel. Noam Elkies first had the idea of doing this for the p55 case, and Stephen Silver constructed the resulting gun shortly after building the original (much larger) p55 Quetzal. Jason Summers later built a p54 version, which is more complicated because the evenness of the period makes the timing problems considerably more difficult.

:Quetzalcoatlus A giant flying dinosaur after which Dieter Leithner named his p54 gun. Usually abbreviated to Quetzal, or simply Q (as in Q54, Q55, Q56, Q-gun, etc.).

:quilt = squaredance

:R = R-pentomino

:R190 A composite conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in July 1996. It is made up of two elementary conduits, HRx131B + BFx59H. After 190 ticks, it produces a Herschel turned 90 degrees clockwise at (24, 16) relative to the input. Its recovery time is 107 ticks. A ghost Herschel in the pattern below marks the output location:

	..........OO.........................
	.......OO..O.........................
	.....OOO.OO..........................
	....O................................
	.O..OOOO.OO..........................
	.OOO...O.OO..........................
	....O................................
	...OO..........................OO....
	...............................O.....
	.............................O.O.....
	.............................OO......
	.....................................
	.....................................
	.....................................
	.....................................
	.................................OO.O
	.................................O.OO
	.....................................
	O.........................OO.........
	O.O.......................OO.........
	OOO..................................
	..O..................................
	.....................................
	.....................................
	.........OO...OO.....................
	..........O...O......................
	.......OOO.....OOO...................
	.......O.........O...................
	.................O.O.................
	..................OO.................
	.....................................
	.....................................
	.....................................
	.....................................
	.....................................
	.........................OOO.........
	.........................O...........
	........................OO...........

:R2D2 (p8) This was found, in the form shown below, by Peter Raynham in the early 1970s. The name derives from a form with a larger and less symmetric stator found by Noam Elkies in August 1994. Compare with Gray counter.

	.....O.....
	....O.O....
	...O.O.O...
	...O.O.O...
	OO.O...O.OO
	OO.O...O.OO
	...O...O...
	...O.O.O...
	....O.O....
	.....O.....

:r5 = R-pentomino

:R64 An elementary conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in September 1995. After 64 ticks, it produces a Herschel rotated 90 degrees clockwise at (11, 9) relative to the input. Its recovery time is 153 ticks, though this can be improved to 61 ticks by adding a from-the-side eater inside the turn to avoid interference from the output Herschel's first natural glider, as shown below. A ghost Herschel in the pattern below marks the output location:

	..........OO...........
	..........OO.....OO....
	.................OO....
	.......................
	.......................
	...............OO......
	...............OO......
	.....................OO
	.....................OO
	.......................
	.......................
	.......................
	.O.....................
	.O.O...................
	.OOO...................
	...O...................
	.......................
	.......................
	.......................
	...OO.OO...............
	..O.O.O.O..............
	..O.O..O...............
	.OO.O........OOO.......
	O...OO.......O.........
	.O.O..O.O...OO.........
	OO.OO..OO..............
R64 is one of the simplest known Spartan conduits, one of the two known Blockic conduits, and one of the few elementary conduits in the original set of sixteen.

:rabbits (stabilizes at time 17331) A 9-cell methuselah found by Andrew Trevorrow in 1986.

	O...OOO
	OOO..O.
	.O.....
The following predecessor, found by Trevorrow in October 1995, has the same number of cells and lasts two generations longer.
	..O....O
	OO......
	.OO.OOO.

:rabbits in pulsar synthesis field, constructed by Otis Arron Schmakel in December 2004. See rabbits. Rabbits, one of the longest-living Methuselah patterns (17,331 generations), and initially only 9 cells, is here contained in a Pulsar Synthesis Field. Rabbits throws off 40 free gliders, 12 of which are killed here by various means, and the other 28 gliders are each fed into Schmakel's Glider to Pulsar Reaction, comprising 3 blocks and a traffic light, which react with the incoming glider to produce a pulsar with a blinker along side, and a great S with a block along side ( initials O. S. ).

..................................................................................................................................................................................................................................O..........................................................................................................................................................................
..................................................................................................................................................................................................................................O..........................................................................................................................................................................
..................................................................................................................................................................................................................................O..........................................................................................................................................................................
.........................................................................................................................................................................................................................................OO..................................................................................................................................................................
..............................................................................................................................................................................................................................OOO...OOO..OO..................................................................................................................................................................
.............................................................................................................................................................................................................................................................................................................................................................................................................
..................................................................................................................................................................................................................................O..........................................................................................................................................................................
..................................................................................................................................................................................................................................O..........................................................................................................................................................................
..................................................................................................................................................................................................................................O..........................................................................................................................................................................
.............................................................................................................................................................................................................................................................................................................................................................................................................
..............................................................................................................................................................OOO............................................................................................................................................................................................................................................
.....................................................................................................................................................................................................................................OO......................................................................................................................................................................
....................................................................................................................O..................................OO...O.....O..................................................................OO......................................................................................................................................................................
....................................................................................................................O..................................OO...O.....O..........................................................................................................................................................................................................................................
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:rake Any puffer whose debris consists of spaceships. A rake is said to be forwards, backwards or sideways according to the direction of the spaceships relative to the direction of the rake. Originally the term "rake" was applied only to forwards c/2 glider puffers (see space rake). Many people prefer not to use the term in the case where the puffed spaceships travel parallel or anti-parallel to the puffer, as in this case they do not rake out any significant region of the Life plane (and, in contrast to true rakes, these puffers cannot travel in a stream, and so could never be produced by a gun).

Although the first rakes (circa 1971) were c/2, rakes of other velocities have since been built. Dean Hickerson's construction of Corderships in 1991 made it easy for c/12 diagonal rakes to be built, although no one actually did this until 1998, by which time David Bell had constructed c/3 and c/5 rakes (May 1996 and September 1997, respectively). Jason Summers constructed a 2c/5 rake in June 2000 (building on work by Paul Tooke and David Bell) and a c/4 orthogonal rake in October 2000 (based largely on reactions found by David Bell).

The smallest possible period for a rake is probably 7, as this could be achieved by a 3c/7 orthogonal backwards glider puffer. The smallest period attained to date is 8 (Jason Summers, March 2001) - see backrake.

:$rats (p6) Found by Dave Buckingham, 1972.

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:R-bee = bun. This name is due to the fact that the pattern is a single-cell modification of a beehive.

:reaction envelope The collection of cells that are alive during some part of a given active reaction. This term is used for Herschel circuits and other stable circuitry, whereas construction envelope is specific to recipes in self-constructing circuitry.

There are some subtleties at the edges of the envelope. Specifically, two reactions that have the exact same set of cells defining their envelopes may have different behavior when placed next to a single-cell protrusion like the tail of an eater1, or one side of a tub. The difference depends on whether two orthogonally adjacent cells at the edge of the envelope are ever simultaneously alive, within the protruding cell's zone of influence.

:reburnable fuse A very rare type of fuse whose output is identical to its input, possibly with some spatial and/or temporal offset. Reburnable fuses are used primarily in the construction of fixed-speed self-supporting macro-spaceships, where the speed of the fuse's burning reaction becomes the speed of the spaceship. Examples include the Caterpillar, Centipede, and waterbear.

:receiver See Herschel receiver.

:recipe = glider synthesis or construction recipe.

:recovery time The number of ticks that must elapse after a signal is sent through a conduit, before another signal can be safely sent on the same path. In general, a lower recovery time means a more useful conduit. For example, the Snark's very low recovery time allowed for the creation of oscillators with previously unknown periods, 43 and 53.

For the most part this is a synonym for repeat time. However, overclocking a complex circuit can often allow it to be used at a repeat time much lower than its safe recovery time.

:rectifier The smallest known 180-degree reflector, discovered by Adam P. Goucher in 2009. It was the smallest and fastest stable reflector of any kind until the discovery of the Snark in 2013. The rectifier has the same output glider as the boojum reflector but a much shorter repeat time of only 106 ticks.

Another advantage of the rectifier is that the output glider is on a transparent lane, so it can be used in logic circuitry to merge two signal paths.

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:recursive filter A toolkit developed by Alexey Nigin in July 2015, which enables the construction of patterns with population growth that asymptotically matches an infinite number of different superlinear functions. Toolkits enabling other, sublinear infinite series had been completed by Dean Hickerson and Gabriel Nivasch in 2006 -- see quadratic filter, exponential filter.

Sublinear functions are possible using the recursive-filter toolkit as well. It can be used to construct a glider-emitting pattern with a slowness rate S(X) = O(log***...*(t)), the nth-level iterated logarithm of t, which asymptotically dominates any primitive-recursive function f(t).

:reflector Any stable or oscillating pattern that can reflect some type of spaceship (usually a glider) without suffering permanent damage. The first known reflector was the pentadecathlon, which functions as a 180-degree glider reflector (see relay). Other examples include the buckaroo, the twin bees shuttle and some oscillators based on the traffic jam reaction. Glider guns can also be made into reflectors, although these are mostly rather large.

In September 1998 Noam Elkies found some fast small-period glider reflectors, with oscillators supplying the required domino sparks at different periods -- a figure-8 produced a p8 reflector, and a p6 pipsquirter produced an equivalent p6 reflector. A more complicated construction allows a p5 reflector (which, as had been anticipated, soon led to a true p55 gun - see Quetzal). And in August 1999 Elkies found a suitable sparker to produce a p7 reflector, allowing the first p49 oscillator to be constructed.

On 6 April 2016, Tanner Jacobi discovered an equally small and simple reaction -- see bumper -- starting with a loaf as bait instead of a boat. This resulted in a series of periodic colour-preserving reflectors, whereas Elkies' reflectors are all colour-changing.

Stable reflectors are special in that if they satisfy certain conditions they can be used to construct oscillators of all sufficiently large periods. It was known for some time that stable reflectors were possible (see universal constructor), but no one was able to construct an explicit example until Paul Callahan did so in October 1996.

All known stable reflectors are very slow. Callahan's original reflector has a repeat time of 4840, soon improved to 1686 and then 894 and then 850. In November 1996 Dean Hickerson found a variant in which this is reduced to 747. Dave Buckingham reduced it to 672 in May 1997 using a somewhat different method, and in October 1997 Stephen Silver reduced it to 623 by a method closer to the original. In November 1998 Callahan reduced this to 575 with a new initial reaction. A small modification by Silver a few days later brought this down to 497.

But in April 2001 Dave Greene found a 180-degree stable reflector with a repeat time of only 202 (see boojum reflector). This reflector won bounties offered by Dietrich Leithner and Alan Hensel. Half of the prize money was recycled into a new prize for a small 90-degree reflector, which in turn was won by Mike Playle's colour-preserving Snark reflector. The Snark is currently the smallest known stable reflector, with a recovery time of 43. Playle has offered a $100 prize for a colour-changing stable reflector contained within a 25 by 25 bounding box, with a recovery time of 50 generations or less.

See also rectifier, glider turner.

:regulator An object which converts input gliders aligned to some period to output gliders aligned to a different period. The most interesting case is a universal regulator, of which several have been constructed by Paul Chapman and others.

:relay Any oscillator in which spaceships (typically gliders) travel in a loop. The simplest example is the p60 one shown below using two pentadecathlons. Pulling the pentadecathlons further apart allows any period of the form 60+120n to be achieved - this is the simplest proof of the existence of oscillators of arbitrarily large period.

	...........................O....O..
	................OO.......OO.OOOO.OO
	.................OO........O....O..
	................O..................
	..O....O...........................
	OO.OOOO.OO.........................
	..O....O...........................

:repeater Any oscillator or spaceship.

:repeat time The minimum number of generations that is possible between the arrival of one object and the arrival of the next. This term is used for things such as reflectors or conduits where the signal objects (gliders or Herschels, for example) will interact fatally with each other if they are too close together, or one will interact fatally with a disturbance caused by the other. For example, the repeat time of Dave Buckingham's 59-step B-heptomino to Herschel conduit (shown under conduit) is 58.

:rephaser The following reaction that shifts the phase and path of a pair of gliders. There is another form of this reaction that reflects the gliders 180 degrees - see glider-block cycle.

	..O..O..
	O.O..O.O
	.OO..OO.
	........
	........
	...OO...
	...OO...

:replicator A finite pattern which repeatedly creates copies of itself. Such objects are known to exist (see universal constructor), but no concrete example is known. The linear propagator may be considered to be the first example of a replicator built in Life, but this is debatable as each of its copies replicate themselves only once, allowing no possibility of superlinear growth.

:reverse fuse A fuse that produces some initial debris, but then burns cleanly. The following is a simple example.

	.............OO
	............O.O
	...........O...
	..........O....
	.........O.....
	........O......
	.......O.......
	......O........
	.....O.........
	....O..........
	...O...........
	..O............
	OO.............

:revolver (p2)

	O............O
	OOO....O...OOO
	...O.O.O..O...
	..O......O.O..
	..O.O......O..
	...O..O.O.O...
	OOO...O....OOO
	O............O

:ring of fire (p2) The following muttering moat found by Dean Hickerson in September 1992.

	................O.................
	..............O.O.O...............
	............O.O.O.O.O.............
	..........O.O.O.O.O.O.O...........
	........O.O.O..OO.O.O.O.O.........
	......O.O.O.O......O..O.O.O.......
	....O.O.O..O..........O.O.O.O.....
	.....OO.O..............O..O.O.O...
	...O...O..................O.OO....
	....OOO....................O...O..
	..O.........................OOO...
	...OO...........................O.
	.O...O........................OO..
	..OOOO.......................O...O
	O.............................OOO.
	.OOO.............................O
	O...O.......................OOOO..
	..OO........................O...O.
	.O...........................OO...
	...OOO.........................O..
	..O...O....................OOO....
	....OO.O..................O...O...
	...O.O.O..O..............O.OO.....
	.....O.O.O.O..........O..O.O.O....
	.......O.O.O..O......O.O.O.O......
	.........O.O.O.O.OO..O.O.O........
	...........O.O.O.O.O.O.O..........
	.............O.O.O.O.O............
	...............O.O.O..............
	.................O................

:rle Run-length encoded. Run-length encoding is a simple (but not very efficient) method of file compression. In Life the term refers to a specific ASCII encoding used for Life patterns (and patterns for other similar cellular automata). This encoding was introduced by Dave Buckingham and is now the usual means of exchanging Life patterns by email or in online forum discussions.

:R-mango A small active reaction, so named because it is a single-cell modification of a mango, but now more commonly known as dove.

:rock Dean Hickerson's term for an eater which remains intact throughout the eating process. The snake in Dave Buckingham's 59-step B-to-Herschel conduit (shown under conduit) is an example. Other still lifes that sometimes act as rocks include the tub, the hook with tail, the eater1 (eating with its tail) and the hat (in Heinrich Koenig's stabilization of the twin bees shuttle).

:roteightor (p8) Found by Robert Wainwright in 1972.

	.O............
	.OOO........OO
	....O.......O.
	...OO.....O.O.
	..........OO..
	..............
	.....OOO......
	.....O..O.....
	.....O........
	..OO..O...O...
	.O.O......O...
	.O.......O....
	OO........OOO.
	............O.

:rotor The cells of an oscillator that change state. Compare stator. It is easy to see that any rotor cell must be adjacent to another rotor cell.

:R-pentomino This is by far the most active polyomino with less than six cells: all the others stabilize in at most 10 generations, but the R-pentomino does not do so until generation 1103, by which time it has a population of 116, including six gliders.

	.OO
	OO.
	.O.

:rule 22 Wolfram's rule 22 is the 2-state 1-D cellular automaton in which a cell is ON in the next generation if and only if exactly one of its three neighbours is ON in the current generation (a cell being counted as a neighbour of itself). This is the behaviour of Life on a cylinder of width 1.

:ruler A pattern constructed by Dean Hickerson in May 2005 that produces a stream of LWSS with gaps in it, such that the number of LWSS between successive gaps follows the "ruler function" (sequence A001511 in The On-Line Encyclopedia of Integer Sequences).

:rumbling river Any oscillator in which the rotor is connected and contained in a strip of width 2. The following p3 example is by Dean Hickerson, November 1994.

	..............OO......OO......OO...O.OO..........
	....O........O..O....O..O....O..O..OO.O..........
	O..O.O....O...OO..O...OO..O...O.O.....O.OO.......
	OOOO.O..OOOOOO..OOOOOO..OOOOOO..OOOOOO.O.O.......
	.....O.O.....O.O.....O.O.....O.O.....O.O......OO.
	..OO.O.O.O.O...O.O.O...O.O.O...O.O.O...O.O.....O.
	.O.....O.O...O.O.O...O.O.O...O.O.O...O.O.O.O.OO..
	.OO......O.O.....O.O.....O.O.....O.O.....O.O.....
	.......O.O.OOOOOO..OOOOOO..OOOOOO..OOOOOO..O.OOOO
	.......OO.O.....O.O...O..OO...O..OO...O....O.O..O
	..........O.OO..O..O....O..O....O..O........O....
	..........OO.O...OO......OO......OO..............

:Rx202 A composite conduit, one of the original sixteen Herschel conduits, discovered by Dave Buckingham in May 1997. It is made up of two elementary conduits, HR143B +BFx59H. After 202 ticks, it produces an inverted Herschel turned 90 degrees clockwise at (7, 32) relative to the input. Its recovery time is 201 ticks. A ghost Herschel in the pattern below marks the output location:

	..............OO...............
	...........OO..O...............
	.........OOO.OO......O.........
	........O..........OOO.........
	.........OOO.OO...O............
	...........O.OO...OO...........
	...............................
	...............................
	...............................
	...............................
	.......................OO......
	.......................O.......
	.....................O.O.......
	.....................OO........
	...............................
	...............................
	...............................
	...............................
	...............................
	...O...........................
	...O.O.........................
	...OOO.........................
	.....O.........................
	......................OO.......
	......................OO.......
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	...............................
	O.OO...........................
	OO.O...........................
	.....................OO........
	.........OO.........O..O..OO...
	.........OO.........O.O....O...
	.....................O.....O.OO
	........................OO.O.O.
	........................O..O..O
	.....................O....O..OO
	.....................OOOOO.....
	...............................
	...................OOOOOOO.....
	...................O..O..O.....
	.................O.O...........
	.................OO............
	...............................
	...............................
	...............................
	...............................
	...............................
	.........OOO...................
	...........O...................
	...........OO..................

:S Usually means big S, but may sometimes mean paperclip.

:sailboat (p16) A boat hassled by a Kok's galaxy, a figure-8 and two eater3s. Found by Robert Wainwright in June 1984.

	........O...........O........
	.......O.O.........O.O.......
	........O...........O........
	.............................
	......OOOOO.......OOOOO......
	.....O....O.......O....O.....
	....O..O.............O..O....
	.O..O.OO.............OO.O..O.
	O.O.O.....O.......O.....O.O.O
	.O..O....O.O.....O.O....O..O.
	....OO..O..O.....O..O..OO....
	.........OO.......OO.........
	.............OO..............
	.............O.O.............
	........O..O..O..............
	.......O.....................
	.....OO..........OOO.........
	..O......OO.O....OOO.........
	.....O...O..O....OOO.........
	.....OOO.O...O......OOO......
	..O...........O.....OOO......
	...O...O.OOO........OOO......
	....O..O...O.................
	....O.OO......O..............
	..........OO.................
	.........O...................
	.....O..O....................

:salvo A collection of spaceships, usually gliders, all traveling in the same direction. Any valid glider construction recipe can be partitioned into no more than four salvos. Compare flotilla.

:sawtooth Any finite pattern whose population grows without bound but does not tend to infinity. (In other words, the population reaches new heights infinitely often, but also infinitely often returns to some fixed value.) Conway's preferred plural is "sawteeth".

The first sawtooth was constructed by Dean Hickerson in April 1991. The current smallest known sawtooth was found by a conwaylife.com forum user with the online handle 'thunk'. It has a bounding box of 74×60, and is the smallest known sawtooth in terms of its minimum repeating population of 177 cells. The following variant has a higher repeating population of 195 and an optimized bounding box of 62×56:

	.....................................................OO.O.....
	.....................................................O.OO.....
	..............................................................
	...........OO.................................................
	...........OO.................................................
	..............................................................
	..............................................................
	..............OO............................OO.......OO.....OO
	....OO........OO.....................................OO.....OO
	.....O.....................................O.O................
	....O......OO............................O..............OO....
	....OO.....OO........................OO.O.OO............OO....
	......................................O.OO....................
	.......................................O......................
	..............................................................
	.................................OO...........................
	........OO.......................OO...........................
	........O.O...................................................
	........O....................OO.....OO........................
	.............................OO.....OO........................
	..............................................................
	..............................................................
	..............................................................
	.....................OOO......................................
	.....................O..O.....................................
	.....................O.OO.....................................
	..............................................................
	..............................................................
	..............................................................
	....................OO............O.........O.................
	....................O..O..........O.O.....OOO.................
	..OOOO...............OOO..........OO.....O....................
	OO....OO.................................OO...................
	OO.....O......................................................
	..OO.O.O..............OO......................................
	.......O..............OO......................................
	...O...O..........................O....O......................
	...O....O.......................OO.....O......................
	.....OOO...O.....................OO...O.O.....................
	.....OO....O.........................OO.OO....................
	...........OO.......................O.....O...................
	.............O.........................O......................
	.............OOO....................OO...OO...................
	..............................................................
	..............................................................
	................O.....................O.......................
	...............O.OOOOO................O.......................
	..............OO.....O...............O........................
	..............OO...O..O.......................................
	......................O.......................................
	................OO.O..O................OO.....................
	...................O..O................OO.....................
	....................OO........................................
	....................OO.....O....O.............................
	.........................OO.OOOO.OO...........................
	...........................O....O.............................
Moving sawtooth patterns combining a fast puffer with a slower spaceship have also been constructed. See also tractor beam.

:SBM = sliding block memory

:Schick engine (c/2 orthogonally, p12) This spaceship, found by Paul Schick in 1972, produces a large spark (the 15 live cells at the rear in the phase shown below) which can be perturbed by other c/2 spaceships to form a variety of puffers. The diagram below shows the smallest form of the Schick engine, using two LWSS. It is also possible to use two MWSS or two HWSS, or even a LWSS and a HWSS.

	OOOO..............
	O...O.........O...
	O...........OO....
	.O..O..OO.....OOO.
	......OOO......OOO
	.O..O..OO.....OOO.
	O...........OO....
	O...O.........O...
	OOOO..............

:Schick ship = Schick engine

:scorpion (p1)

	...O...
	.OOO...
	O...OO.
	O.O.O.O
	.OO.O.O
	.....O.

:scrubber (p2) Found in 1971.

	....O......
	..OOO......
	.O.........
	.O..OOO....
	OO.O...O...
	...O...O...
	...O...O.OO
	....OOO..O.
	.........O.
	......OOO..
	......O....

:SE = switch engine

:seal (c/6 diagonally, p6) The first diagonal c/6 spaceship, found by Nicolay Beluchenko in September 2005.

	...O..OO..........................
	.OOO.O.O.O........................
	.O..OOO..OO.......................
	O..OOOOOO.O.OOO...................
	.O..OOO.O.OOOOO...................
	......O.O.O.O.....................
	O.O...O.O.OOOOO...................
	O..O.O..O.OO...O..................
	...O..OO.......OOO................
	.O...OOOOO.OOO..OO................
	....O.........O...................
	..O.O.........O...................
	....OO.OOOOO...O..................
	......O.OOO..O.....OO.............
	......O..O...O.OOO.OO.............
	........OO...OOO.O..O...O.........
	........OO....OO.OOOO...OOO.......
	...................O.O..O.........
	.............O.O.....OO..OO.......
	.............O..O.....O.OOO.....O.
	.............O...O....OO..O...O..O
	...............OOO.....OO........O
	...............O.O..O..O.....OO..O
	.................O..OO.OO.O..O....
	................O.......O.O.......
	.................O...OOOO.........
	..................O...O...........
	..................................
	.......................O..........
	......................O.O.........
	.....................OO...........
	.....................O.O..........
	.....................OO...........
	.......................O..........
	......................O...........

:second glider domain The second glider domain of an edge shooter is the set of displacements (in space and time, relative to the glider stream emitted by the edge shooter) that a glider stream may have without interfering with the edge shooter. This is useful to know, because edge shooters are often used to generate glider streams very close to other glider streams.

:second natural glider The glider produced at T=72 during the evolution of a Herschel. This is the common edge-shooting glider output used in the NW31 converter and several other converter variants.

:seed A constellation of still lifes and/or oscillators, which can be converted into another Life object when it is struck by one or more gliders. Usually the resulting object is a rare still life or spaceship, more complex than the original constellation. Spartan single-glider (1G) seeds are more commonly seen than multi-glider seeds, because a Spartan 1G seed can be readily constructed and triggered using a slow salvo. See also freeze-dried. For example, the following is a 14sL 1G seed for a c/7 loafer spaceship.

	...................................O..........
	..................................O...........
	..................................OOO.........
	.............OO...............................
	..............O...............................
	..............O.O.............................
	...............OO.............................
	..............................................
	...O..........................................
	..O.O.........................................
	.O.O..........................................
	.OO...........................................
	..............OO..............................
	.............O.O..............................
	.............OO...............................
	..............................................
	..............................................
	..............................................
	....................OO........................
	...................O.O........................
	..........O.........O.........................
	.........O.O....O.............................
	..........OO...O.O............................
	..............O.O.............................
	..............OO..............................
	..............................................
	.............................................O
	.........................OO................OOO
	....................OO...OO...............O...
	...................O..O...................OO..
	.O.................O..O.......................
	O.O.................OO........................
	.OO...........................................
	..............................................
	..............................................
	..............................................
	.....................OO.......................
	.....................O.O....OO................
	......................O.....O.O...............
	.............................OO...............
	.................................OO...........
	.................................OO...........
	..............................................
	..............................................
	......................OO......................
	.....................O..O.....................
	.....................O..O.....................
	......................OO......................

:Seeds of Destruction Game An interactive search application written by Paul Chapman in 2013. Its primary purpose was to assist in the design of self-destruct circuits in self-constructing circuitry. It has also regularly been helpful in completing glider syntheses, and was used to find the 31c/240 base reaction for the shield bug and Centipede spaceships.

:self-constructing A type of pattern, generally a spaceship, that contains encoded construction information about itself, and makes a complete copy of itself using those instructions. The Gemini, linear propagator, Demonoids and Orthogonoid are examples of self-constructing patterns. Self-constructing spaceships often have trivially adjustable speeds. In many cases, the direction of travel can also be altered, less easily, by changing the encoded construction recipe. Compare self-supporting.

:self-supporting A type of pattern, specifically a spaceship, that constructs signals or tracks or other scaffolding to assist its movement, but does not contain complete information about its own structure. Examples include the Caterpillar, Centipede, HBK, waterbear, and the Caterloopillars. In general a self-supporting pattern cannot be trivially adjusted to alter its speed or direction; the HBK's variable speed is an exception, but its direction of travel is fixed. Compare self-constructing.

:semi-Snark A small 90-degree glider reflector requiring two input gliders on the same lane for each output glider. It was discovered by Sergei Petrov on 1 July 2013, using a custom-written search utility. It functions as a very compact period doubler in some signal circuitry, for example the linear propagator.

	......O..........OO
	.......OO........O.
	......OO.......O.O.
	...............OO..
	..........O........
	OO.........OO......
	OO........OO.......
	...................
	...................
	.................OO
	..........OO.....OO
	..........OO.......
	...................
	.....O.............
	....O.O............
	....OO......OO.....
	............O......
	.............OOO...
	...............O...

:sesquihat (p1) Halfway between a hat and a twinhat.

	....O
	OO.O.O.
	.O.O.O.
	.O.O.OO
	..O...

:SGR Abbreviation for stable glider reflector. This term is no longer in use.

:shield bug (31c/240 orthogonally, p240) The first 31c/240 macro-spaceship, constructed by Dave Greene on September 9, 2014.

:shillelagh (p1)

	OO...
	O..OO
	.OO.O

:ship (p1) The term is also used as a synonym of spaceship.

	OO.
	O.O
	.OO

:ship in a bottle (p16) Found by Bill Gosper in August 1994. See also bottle.

	....OO......OO....
	...O..O....O..O...
	...O.O......O.O...
	.OO..OOO..OOO..OO.
	O......O..O......O
	O.OO..........OO.O
	.O.O..........O.O.
	...OO...OO...OO...
	.......O.O........
	.......OO.........
	...OO........OO...
	.O.O..........O.O.
	O.OO..........OO.O
	O......O..O......O
	.OO..OOO..OOO..OO.
	...O.O......O.O...
	...O..O....O..O...
	....OO......OO....

:ship on boat = ship tie boat

:ship on ship = ship-tie

:ship-tie (p1) The name is by analogy with boat-tie.

	OO....
	O.O...
	.OO...
	...OO.
	...O.O
	....OO

:ship tie boat (p1)

	OO....
	O.O...
	.OO...
	...OO.
	...O.O
	....O.

:short keys (p3) Found by Dean Hickerson, August 1989. See also bent keys and odd keys.

	.O........O.
	O.OOO..OOO.O
	.O..O..O..O.
	....O..O....

:shoulder The fixed upper end of a construction arm, generally consisting of one or more glider guns or edge shooters aimed at an elbow object.

:shuttle Any oscillator which consists of an active region moving back and forth between stabilizing objects. The most well-known examples are the queen bee shuttle (which has often been called simply "the shuttle") and the twin bees shuttle. See also p54 shuttle and Eureka. Another example is the p72 R-pentomino shuttle that forms part of the pattern given under factory.

:siamese A term used in naming certain still lifes (and the stator part of certain oscillators). It indicates that the object consists of two smaller objects sharing two or more cells. See snake siamese snake and loaf siamese barge for examples.

:side Half a sidewalk. In itself this is unstable and requires an induction coil.

	OO...
	O.OOO
	....O

:sidecar A small tagalong for a HWSS that was found by Hartmut Holzwart in 1992. The resulting spaceship (shown below) has a phase with only 24 cells, making it in this respect the smallest known spaceship other than the standard spaceships and some trivial two-spaceship flotillas derived from them. Note also that a HWSS can support two sidecars at once.

	.O......
	O.....O.
	O.....O.
	OOOOO.O.
	........
	....OO..
	..O....O
	.O......
	.O.....O
	.OOOOOO.

:side-shooting gun = slide gun

:sidesnagger A Spartan eater found by Chris Cain in May 2015 with functionality similar to the eater5, as shown below. It has one lane less diagonal clearance on the high-clearance side than other eater5 variants, due to the presence of the boat. See also highway robber.

	.O...........
	..O..........
	OOO..........
	.............
	......O......
	.....O.......
	.....OOO.....
	.............
	.............
	......O......
	.....O.O.....
	....O..O...OO
	.....OO....OO
	.O...........
	O.O..........
	OO...........
	......OO.....
	......OO.....

:side-tracking See universal constructor.

:sidewalk (p1)

	.OO.OO
	..O.O.
	.O..O.
	.O.O..
	OO.OO.

:siesta (p5) Found by Dave Buckingham in 1973. Compare sombreros.

	...........OO...
	...OO.....O.O...
	...O.O....O.....
	.....O...OO.O...
	...O.OO.....OOO.
	.OOO.....O.O...O
	O...O.O.....OOO.
	.OOO.....OO.O...
	...O.OO...O.....
	.....O....O.O...
	...O.O.....OO...
	...OO...........

:signal Movement of information through the Life universe. Signals can be carried by spaceships, fuses, drifters, or conduits. Spaceships can only transfer a signal at the speed of the spaceship, while fuses can transfer a signal at speeds up to the speed of light.

In practice, many signals are encoded as the presence or absence of a glider or other spaceship at a particular point at a particular time. Such signals can be combined by the collision of gliders to form logic operations such as AND, OR, and NOT gates. Signals can be duplicated using glider duplicators or other fanout devices, and can be used up by causing perturbations on other parts of the Life object.

Signals are used in Herschel conduit circuitry, universal constructors, macro-spaceships, and other computational patterns such as the pi calculator and Osqrtlogt patterns.

:signal elbow A conduit with signal output 90 degrees from its input. This term is commonly used only for signal wires, particularly 2c/3 signals. A Snark could reasonably be called a "glider elbow", but glider reflector is the standard term. A signal elbow with a recovery time less than 20 ticks would enable a trivial proof that Conway's Life is omniperiodic.

Relatively small composite MWSS elbows can now be constructed, using Tanner Jacobi's 2015 discovery of a small H-to-MWSS component. The extra beehive can be easily cleaned up in various ways using Snarks, syringes or Herschel conduits.

:Silver G-to-H A variant of the Silver reflector made by substituting an Fx119 conduit for the final NW31, allowing a Herschel output as well as the beehive-annihilating reset glider. It is still Spartan and retains the recovery time of 497 ticks.

:Silver reflector A stable glider reflector found by Stephen Silver in November 1998, by substituting an NW31 converter for the second Fx77 conduit in the Callahan G-to-H found a few days previous. The repeat time is 497 ticks:

	........O.............O.......................................
	......O.O...........OOO.......................................
	.......OO..........O..........................................
	...................OO.........................................
	....OO........................................................
	.....O........................................................
	.....O.O......................................................
	......OO..........O...........................................
	.................O.O..........................................
	.................O.O..........................................
	..................O....OO.....................................
	......OO...............O.O....................................
	.....O.O.................O....................................
	.....O...................OO...................................
	....OO........................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	...............OO.............................................
	...............OO.............................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	...OO.........................................................
	....O.........................................................
	....O.O.......................................................
	.....OO.......................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	......OO...............OO.....................................
	......OO...............O.O....................................
	.........................O....................................
	.........................OO...................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	..............................................................
	...................O..........................................
	.................OOO..........................................
	................O.............................................
	................OO...................OO.......................
	....................OO................O.......................
	.....................O................O.O.....................
	...................O...................OO.....................
	...................OO.........................................
	..............................................................
	..............................................................
	............................................................OO
	............................................................OO
	..............................................................
	......................OO......................................
	...OO.................OO......................................
	...OO.........................................................
	..............................................................
	..............................................................
	..OO..........................................................
	...O..........................................................
	OOO............OO.............................................
	O..............O..............................................
	................OOO...........................................
	..................O...........................................
	..............................................................
	..................................................OO..........
	..................................................OO..........

:Silver's p5 (p5) The following oscillator found by Stephen Silver in February 2000:

	OO.........
	O..........
	.O..O......
	...OO......
	...O...O.OO
	..O....OO.O
	..OO.......

As this has no spark, it appears useless. Nonetheless, in March 2000, David Eppstein found a way to use it to reduce the size of Noam Elkies' p5 reflector.

:Simkin glider gun A Herschel-based period 120 glider gun discovered by Michael Simkin in April 2015. It consists of a Herschel running through two B60 conduits. In terms of its 36-cell minimum population, it is one of the smallest known guns, sharing the record with the Gosper glider gun. In the double-barreled form, as well as the pseudo-period, snake-stabilized form shown below, it is the absolute record holder.

	OO.....OO........................
	OO.....OO........................
	.................................
	....OO...........................
	....OO...........................
	.................................
	.................................
	.................................
	.................................
	......................OO.OO......
	.....................O.....O.....
	.....................O......O..OO
	.....................OOO...O...OO
	..........................O......
	.................................
	.................................
	.................................
	.................................
	........................O.OO.....
	........................OO.O.....

:single-arm A type of universal constructor using just one construction arm and slow salvo techniques to construct, usually, Spartan or near-Spartan circuitry. Compare two-arm.

:single-channel A universal construction method discovered by Simon Ekstrom in December 2015. The initial elbow operation toolkit was near-minimal -- just one push, one pull, and one output glider of each colour -- but later searches produced a much larger library. See colour of a glider

:single-lane = single-channel.

:singular flip flop (p2) Found by Robert Wainwright, July 1972.

	..O...
	..O.O.
	O....O
	OOOOOO
	......
	..OO..
	..OO..

:sinking ship = canoe

:six Ls (p3) This is a compact form of loading dock.

	...O...
	.OOO..O
	O...OOO
	OOO....
	....OOO
	OOO...O
	O..OOO.
	...O...

:sixty-nine (p4) Found by Robert Wainwright, October 1978.

	.........O...........
	........O.O..........
	.....................
	......O...OO.........
	.....O.....O.........
	......O.O............
	........OO......O....
	................O....
	..O.....OO....OOO....
	..O...........OO.....
	OOO.......OO..OO..OOO
	OO......O.OO....OOO..
	OO..OOO.O.O.....OOO..
	..OOO................
	..OOO......O.........
	..........O.O........
	.....................
	........O...OO.......
	.......O.....O.......
	........O.O..........
	..........OO.........

:skewed quad (p2)

	.OO....
	.O...OO
	..O.O.O
	.......
	O.O.O..
	OO...O.
	....OO.

:skewed traffic light (p3) Found by Robert Wainwright, August 1989.

	.............OO.........
	............O..O........
	.............O.O........
	.........OO...O.........
	..........O.OO..........
	............O...........
	............O...........
	........................
	OO........OOO......O....
	OOOO.O........O...OO....
	O.O..OOO.O....O.........
	.........O....O.OOO..O.O
	....OO...O........O.OOOO
	....O......OOO........OO
	........................
	...........O............
	...........O............
	..........OO.O..........
	.........O...OO.........
	........O.O.............
	........O..O............
	.........OO.............

:sL Still life. This abbreviation is used most often in rough measurements of the complexity of a Spartan constellation.

:slide gun A gun which fires sideways from an extending arm. The arm consists of streams of spaceships which are pushing a pattern away from the body of the gun and releasing an output spaceship every time they do so. Each output spaceship therefore travels along a different path.

Dieter Leithner constructed the first slide gun in July 1994 (although he used the term "side shooting gun"). The following pattern shows the key reaction of this slide gun. The three gliders shown will push the block one cell diagonally, thereby extending the length of the arm by one cell, and at the same time they release an output glider sideways. (In 1999, Jason Summers constructed slide guns using other reactions.)

	..............OO.
	..............OO.
	........OOO......
	..........O......
	.........O.....OO
	..............O.O
	................O
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.................
	.O...............
	.OO..............
	O.O..............

:sliding block memory A memory register whose value is stored as the position of a block. The block can be moved by means of glider collisions - see block pusher for an example.

In Conway's original formulation (as part of his proof of the existence of a universal computer in Life) 2 gliders were used to pull the block inwards by three diagonal spaces, and 30 gliders were used to push it out by the same amount. Dean Hickerson later greatly improved on this, finding a way to pull a block inwards by one diagonal space using 2 gliders, and push it out using 3 gliders. In order for the memory to be of any use there also has to be a way to read the value held. It suffices to be able to check whether the value is zero (as Conway did), or to be able to detect the transition from one to zero (as Hickerson did).

Dean Hickerson's sliding block memory is used in Paul Chapman's URM.

:slow elbow A movable elbow in a construction arm toolkit that is controlled by a slow salvo, which most likely comes from a previous construction elbow. Unlike a standard elbow which is generally fixed on a single construction lane or at least within a narrow range, a slow elbow can move freely in two dimensions as long as there is room for it.

:slow glider construction Construction an object by a "slow salvo" of gliders all coming from the same direction, in such a way that timing of the gliders does not matter as long as they are not too close behind one another. This type of construction requires an initial seed object, such as a block, which is modified by each glider in turn until the desired object is produced.

In May 1997, Nick Gotts produced a slow glider construction of a block-laying switch engine from a block, using a slow salvo of 53 gliders. Constructions like this are important in the study of sparse Life, as they will occur naturally as gliders created in the first few generations collide with blonks and other debris.

Slow glider constructions are also useful in some designs for universal constructors. However, in this case the above definition is usually too restrictive, and it is desirable to allow constructions in which some gliders in the salvo are required to have a particular timing modulo 2 (a "p2 slow salvo"). This gives much greater flexibility, as blinkers can now be freely used in the intermediate construction steps.

:slow salvo See slow glider construction.

:small fish = LWSS

:small lake (p1) See also lake.

	....O....
	...O.O...
	...O.O...
	.OO...OO.
	O.......O
	.OO...OO.
	...O.O...
	...O.O...
	....O....

:smiley (p8) Found by Achim Flammenkamp in July 1994 and named by Alan Hensel.

	OO.O.OO
	...O...
	O.....O
	.OOOOO.
	.......
	.......
	OOO.OOO

:SMM breeder See breeder.

:smoke Debris which is fairly long-lived but eventually dies completely. Basically, a large spark. This term is used especially when talking about the output from a spaceship - see smoking ship.

:smoking ship A spaceship which produces smoke. If the smoke extends past the edge of the rest of the spaceship, then it can be used to perturb other objects as the spaceship passes by. Running gliders into the smoke is often a good way to turn or duplicate the them, or convert them into other objects. Sometimes the smoke from a smoking ship may itself be perturbed by accompanying spaceships in order to form a puffer. A simple example of a smoking ship is the Schick engine.

:snacker (p9) Found by Mark Niemiec in 1972. This is a pentadecathlon with stabilizers which force it into a lower period.

	OO................OO
	.O................O.
	.O.O............O.O.
	..OO............OO..
	.......O....O.......
	.....OO.OOOO.OO.....
	.......O....O.......
	..OO............OO..
	.O.O............O.O.
	.O................O.
	OO................OO
The stabilizers make the domino spark largely inaccessible, but the snacker is extensible, as shown in the next diagram, and so a more accessible p9 domino spark can be obtained. In April 1998 Dean Hickerson found an alternative stabilizer that is less obtrusive than the original one, and this is also shown in this diagram.
	OO................................
	.O................................
	.O.O.........................OO...
	..OO.......................O..O...
	.......O....O..............OOO....
	.....OO.OOOO.OO...O....O......OOO.
	.......O....O...OO.OOOO.OO...O...O
	..OO..............O....O......OOO.
	.O.O.......................OOO....
	.O.........................O..O...
	OO...........................OO...
An end can also be stabilized by killer candlefrobras.

:snail (c/5 orthogonally, p5) The first known c/5 spaceship, discovered by Tim Coe in January 1996. For some time it was the slowest known orthogonal spaceship.

	.O....................................
	.O....................................
	O.....................................
	.OOO.................OOO...OOO........
	.OO.O.........O...O.O......OOO........
	..O...........OO.O.......O....OOOO....
	......O......O...O.O...OO.O.....OO....
	...O..O.OOO...OO.........O........OO.O
	...OO.O.....O.....O.................O.
	.........O.OOOOOOO....................
	......................................
	.........O.OOOOOOO....................
	...OO.O.....O.....O.................O.
	...O..O.OOO...OO.........O........OO.O
	......O......O...O.O...OO.O.....OO....
	..O...........OO.O.......O....OOOO....
	.OO.O.........O...O.O......OOO........
	.OOO.................OOO...OOO........
	O.....................................
	.O....................................
	.O....................................

:snake (p1)

	OO.O
	O.OO

:snake bit An alternative name for a boat-bit. Not a very sensible name, because various other things can be used instead of a snake.

:snake bridge snake (p1)

	....OO
	....O.
	.....O
	....OO
	OO.O..
	O.OO..

:snake dance (p3) Found by Robert Wainwright, May 1972.

	...OO.O..
	...O.OO..
	OO.O.....
	.O..O.OOO
	O..O.O..O
	OOO.O..O.
	.....O.OO
	..OO.O...
	..O.OO...

:snake pit This term has been used for two different oscillators: the p2 snake pit (essentially the same as fore and back)

	O.OO.OO
	OO.O.O.
	......O
	OOO.OOO
	O......
	.O.O.OO
	OO.OO.O
and the p3 snake pit.
	.....OO....
	....O..O...
	....O.OO...
	.OO.O......
	O.O.O.OOOO.
	O.........O
	.OOOO.O.O.O
	......O.OO.
	...OO.O....
	...O..O....
	....OO.....

:snake siamese snake (p1)

	OO.OO.O
	O.OO.OO

:Snark A small stable 90-degree glider reflector with a repeat time of 43 ticks, discovered by Mike Playle on 25 April 2013 using a search utility he wrote called Bellman. Compare boojum reflector. Four common Snark variants are shown below -- Playle's original (top), and variants by Heinrich Koenig, Simon Ekstrom, and Shannon Omick (left, bottom, and right, respectively):

	.............................OO....................
	............................O.O....................
	......................OO....O......................
	....................O..O..OO.OOOO..................
	....................OO.O.O.O.O..O..................
	.......................O.O.O.O.....................
	.......................O.O.OO......................
	........................O..........................
	...................................................
	.....................................OO............
	............................OO.......O.............
	............................OO.....O.O.............
	.........O.........................OO..............
	.........OOO.......................................
	............O........O.............................
	...........OO.......O..............................
	....................OOO............................
	...................................................
	...OO..............................................
	...O.....................OO........................
	OO.O......................O........................
	O..OOO....OO...........OOO.........................
	.OO...O...OO...........O......................O....
	...OOOO.....................OO..............OOOOO..
	...O...............OO........O.............O.....O.
	....OOO............O.O.......O.O............OOO..O.
	.......O.............O........OO...............O.OO
	..OOOOO..............OO.....................OOOO..O
	.O..O......................O...........OO...O...OO.
	.OO......................OOO...........OO....OOO...
	........................O......................O...
	........................OO.....................O.OO
	..............................................OO.OO
	...................................................
	...................................................
	......................................OO...........
	......................................O............
	.......................................OOO.........
	..............OO.........................O.........
	.............O.O.....OO............................
	.............O.......OO............................
	............OO.....................................
	...................................................
	..........................O........................
	................OO....OO.O.O.......................
	...............O..O..O.O.O.O.......................
	................OO...O.O.O.OO......................
	..................OOOO.OO..O.......................
	..................O...O....O.......................
	...................O..O.OOO........................
	....................O.O.O..........................
	.....................O.............................

:SNG = second natural glider.

:SODGame = Seeds of Destruction Game

:sombrero One half of sombreros or siesta.

:sombreros (p6) Found by Dave Buckingham in 1972. If the two halves are moved three spaces closer to one another then the period drops to 4, and the result is just a less compact form of Achim's p4. Compare also siesta.

	...OO........OO...
	...O.O......O.O...
	.....O......O.....
	...O.OO....OO.O...
	.OOO..........OOO.
	O...O.O....O.O...O
	.OOO..........OOO.
	...O.OO....OO.O...
	.....O......O.....
	...O.O......O.O...
	...OO........OO...

:soup A random initial pattern, often assumed to cover the whole Life universe.

:space dust A part of a spaceship or oscillator which looks like a random mix of ON and OFF cells. It is usually very difficult to find a glider synthesis for an object that consists wholly or partly of space dust.

:spacefiller Any pattern that grows at a quadratic rate by filling space with an agar. The first example was found in September 1993 by Hartmut Holzwart, following a suggestion by Alan Hensel. The diagram below shows a smaller spacefiller found by Tim Coe. See also Max. Spacefillers can be considered as breeders (more precisely, MMS breeders), but they are very different from ordinary breeders. The word "spacefiller" was suggested by Harold McIntosh and soon became the accepted term.

	..................O........
	.................OOO.......
	............OOO....OO......
	...........O..OOO..O.OO....
	..........O...O.O..O.O.....
	..........O....O.O.O.O.OO..
	............O....O.O...OO..
	OOOO.....O.O....O...O.OOO..
	O...OO.O.OOO.OO.........OO.
	O.....OO.....O.............
	.O..OO.O..O..O.OO..........
	.......O.O.O.O.O.O.....OOOO
	.O..OO.O..O..O..OO.O.OO...O
	O.....OO...O.O.O...OO.....O
	O...OO.O.OO..O..O..O.OO..O.
	OOOO.....O.O.O.O.O.O.......
	..........OO.O..O..O.OO..O.
	.............O.....OO.....O
	.OO.........OO.OOO.O.OO...O
	..OOO.O...O....O.O.....OOOO
	..OO...O.O....O............
	..OO.O.O.O.O....O..........
	.....O.O..O.O...O..........
	....OO.O..OOO..O...........
	......OO....OOO............
	.......OOO.................
	........O..................

:space nonfiller Any pattern that expands indefinitely to affect every cell in the Life plane, but leaves an expanding region of vacuum at its center. Compare spacefiller; see also antstretcher. The first nonfiller was discovered by Jason Summers on 14 April 1999:

	...................OOO...............
	..................O..O...............
	............OOO......O....OOO........
	............O..O.O...O....O..O.......
	............O..O.O...O....O..O.......
	..........O..........O..O.O.OOO......
	..........OO..OO..O.O....O.....O.....
	........O................OO..OOO.....
	........OOO.O.OO..........O......O...
	......O........O.........O.O...OOO...
	......OOO.....O..........O........O..
	...O.O.........................O.OOO.
	..OOOOO.O..........................O.
	.OO......O.....................OOOOO.
	OO....OO..................O.O........
	.O.O...O..O...............O..O...O.O.
	........O.O..................OO....OO
	.OOOOO.....................O......OO.
	.O..........................O.OOOOO..
	.OOO.O.........................O.O...
	..O........O..........O.....OOO......
	...OOO...O.O.........O........O......
	...O......O..........OO.O.OOO........
	.....OOO..OO................O........
	.....O.....O....O.O..OO..OO..........
	......OOO.O.O..O..........O..........
	.......O..O....O...O.O..O............
	.......O..O....O...O.O..O............
	........OOO....O......OOO............
	...............O..O..................
	...............OOO...................

:space rake The following p20 forwards glider rake, which was the first known rake. It consists of an ecologist with a LWSS added to turn the dying debris into gliders.

	...........OO.....OOOO
	.........OO.OO...O...O
	.........OOOO........O
	..........OO.....O..O.
	......................
	........O.............
	.......OO........OO...
	......O.........O..O..
	.......OOOOO....O..O..
	........OOOO...OO.OO..
	...........O....OO....
	......................
	......................
	......................
	..................OOOO
	O..O.............O...O
	....O................O
	O...O............O..O.
	.OOOO.................

:spaceship Any finite pattern that reappears (without additions or losses) after a number of generations and displaced by a non-zero amount. By far the most natural spaceships are the glider, LWSS, MWSS and HWSS, followed by the Coe ship which has also evolved multiple times from random asymmetric soup starting conditions. See also the entries on individual spaceship speeds: c/2 spaceship, c/3 spaceship, c/4 spaceship, c/5 spaceship, c/6 spaceship, c/7 spaceship, c/10 spaceship, c/12 spaceship, 2c/5 spaceship, 2c/7 spaceship, 3c/7 spaceship, and 17c/45 spaceship.

It is known that there exist spaceships travelling in all rational directions and at arbitrarily slow speeds (see universal constructor). Before 1989, however, the only known examples travelled at c/4 diagonally (gliders) or c/2 orthogonally (everything else).

In 1989 Dean Hickerson started to use automated searches to look for new elementary spaceships, and had considerable success. Other people have continued these searches using tools such as lifesrc and gfind, and as a result we now have a great variety of elementary spaceships travelling at fifteen different velocities. The following table details the discovery of elementary spaceships with new velocities as of August 2017.

	--------------------------------------------------------------
	Speed Direction  First Discovery   Discoverer             Date
	--------------------------------------------------------------
	c/4   diagonal   glider            Richard Guy            1970
	c/2   orthogonal LWSS              John Conway            1970
	c/3   orthogonal 25P3H1V0.2        Dean Hickerson     Aug 1989
	c/4   orthogonal 119P4H1V0         Dean Hickerson     Dec 1989
	c/12  diagonal   Cordership        Dean Hickerson     Apr 1991
	2c/5  orthogonal 44P5H2V0          Dean Hickerson     Jul 1991
	c/5   orthogonal snail             Tim Coe            Jan 1996
	2c/7  orthogonal weekender         David Eppstein     Jan 2000
	c/6   orthogonal dragon            Paul Tooke         Apr 2000
	c/5   diagonal   295P5H1V1         Jason Summers      Nov 2000
	c/6   diagonal   seal              Nicolay Beluchenko Sep 2005
	c/7   diagonal   lobster           Matthias Merzenich Aug 2011
	c/7   orthogonal loafer            Josh Ball          Feb 2013
	c/10  orthogonal copperhead        zdr                Mar 2016
	3c/7  orthogonal spaghetti monster Tim Coe            Jun 2016
	--------------------------------------------------------------

Several infinite families of adjustable-velocity macro-spaceships have also been constructed, of which the first was Gabriel Nivasch's Caterpillar from December 2004. The macro-spaceship with the widest range of possible speeds is Michael Simkin's Caterloopillar from April 2016; in theory it supports any rational speed strictly less than c<4. A somewhat similar design supporting any rational speed strictly less than c/2 has been shown to be feasible, but as of August 2017 no explicit examples have been constructed.

A period p spaceship that displaces itself (m,n) during its period, where m>=n, is said to be of type (m,n)/p. It was proved by Conway in 1970 that p>=2m+2n. (This follows immediately from the easily-proved fact that a pattern cannot advance diagonally at a rate greater than one half diagonal step every other generation.)

:Spaceships in Conway's Life A series of articles posted by David Bell to the newsgroup comp.theory.cell-automata during the period August-October 1992 that described many of the new spaceships found by himself, Dean Hickerson and Hartmut Holzwart. Bell produced an addendum covering more recent developments in 1996.

:spaghetti monster The first 3c/7 spaceship, found by Tim Coe in June 2016. The spaceship travels orthogonally, has a minimum of 702 live cells and fits in a 27×137 bounding box.

:spark A pattern that dies. The term is typically used to describe a collection of cells periodically thrown off by an oscillator or spaceship, but other dying patterns, particularly those consisting or only one or two cells (such as produced by certain glider collisions, for example), are also described as sparks. For examples of small sparks see unix and HWSS. For an example of a much larger spark see Schick engine.

:spark coil (p2) Found in 1971.

	OO....OO
	O.O..O.O
	..O..O..
	O.O..O.O
	OO....OO

:sparker An oscillator or spaceship that produces sparks. These can be used to perturb other patterns without being themselves affected.

:sparky A certain c/4 tagalong, shown here attached to the back of a spaceship.

	..........O....................
	..........O...............OO...
	......OO.O.OOO..........OO...O.
	O.OO.OO.OO..O.O...OO.OOOO......
	O...OO..O.OO..OOO..O.OO..OO...O
	O.OO....OOO.O.OOO......OO..O...
	........OO.O...............O..O
	O.OO....OOO.O.OOO......OO..O...
	O...OO..O.OO..OOO..O.OO..OO...O
	O.OO.OO.OO..O.O...OO.OOOO......
	......OO.O.OOO..........OO...O.
	..........O...............OO...
	..........O....................

:sparse Life This refers to the study of the evolution of a Life universe which starts off as a random soup of extremely low density. Such a universe is dominated at an early stage by blocks and blinkers (often referred to collectively as blonks) in a ratio of about 2:1. Much later it will be dominated by simple infinite growth patterns (presumably mostly switch engines). The long-term fate of a sparse Life universe is less certain. It may possibly become dominated by self-reproducing patterns (see universal constructor), but it is not at all clear that there is any mechanism for these to deal with the all junk produced by switch engines.

:Spartan A pattern composed of subunits that can be easily constructed in any orientation, usually with a slow salvo. Generally this means that the pattern is a constellation of Spartan still lifes -- block, tub, boat, hive, ship, loaf, eater1, or pond. Other small objects may sometimes be counted as Spartan, including period-2 oscillators -- mainly blinkers, but also beacons or toads, which may occur as intermediate targets in slow salvo recipes. Most self-constructing patterns are Spartan or mostly Spartan, to simplify the process of self-construction.

:speed of light A speed of one cell per generation, the greatest speed at which any effect can propagate. Usually denoted c.

:S-pentomino Conway's name for the following pentomino, which rapidly dies.

	..OO
	OOO.

:spider (c/5 orthogonally, p5) This is the smallest known c/5 spaceship, and was found by David Bell in April 1997. Its side sparks have proved very useful in constructing c/5 puffers, including rakes. See also PPS.

	......O...OOO.....OOO...O......
	...OO.OOOOO.OO...OO.OOOOO.OO...
	.O.OO.O.....O.O.O.O.....O.OO.O.
	O...O.O...OOOOO.OOOOO...O.O...O
	....OOO.....OO...OO.....OOO....
	.O..O.OOO.............OOO.O..O.
	...O.......................O...

:spiral (p1) Found by Robert Wainwright in 1971.

	OO....O
	.O..OOO
	.O.O...
	..O.O..
	...O.O.
	OOO..O.
	O....OO

:spiral growth A self-constructing pattern built by Dave Greene in August 2014 that uses four universal constructors (UCs) arranged in a diamond to build four more UCs in a slightly larger diamond. This was the first B3/S23 pattern that exhibited spiral growth, and as of 2016 it isthe only such pattern, though a much smaller version could now be designed with a single-channel construction toolkit.

:splitter A signal converter that accepts a single input signal and produces two or more output signals, usually of the same type as the input. An older term for this is fanout, or "fanout device".

A sub-category is the one-time splitter, which is not technically a converter because it can only be used once. One-time splitters are usually small constellations that produce two or more clean gliders when struck by a single glider. In other words, they are multi-glider seeds. These are important for constructing self-destruct circuitry in self-constructing spaceships.

:SPPS (c/5 orthogonally, p30) The symmetric PPS. The original PPS found by David Bell in May 1998. Compare APPS.

:sqrtgun Any glider-emitting pattern which emits its nth glider at a time asymptotically proportional to n2. The first examples were constructed by Dean Hickerson around 1991. See also quadratic filter, exponential filter, recursive filter.

:squaredance The p2 agar formed by tiling the plane with the following pattern. Found by Don Woods in 1971.

	OO......
	....OO..
	..O....O
	..O....O
	....OO..
	OO......
	...O..O.
	...O..O.

:squirter = pipsquirter

:S-spiral = big S

:stable A pattern is said to be stable if it is a parent of itself. See still life.

:stable pseudo-Heisenburp A multi-stage converter constructed by Dave Greene in January 2007, using a complex recipe found by Noam Elkies to insert a signal into a 2c/3 wire. The wire's high transmission speed allows a signal from a highway robber to catch up to a salvo of gliders. Ultimately the mechanism restores the key glider -- which was destroyed by the highway robber in the first stage of the converter -- to its exact original position in the salvo.

Much smaller stable pseudo-Heisenburp devices have since been designed that use simple 0-degree glider seed constellations instead of a 2c/3 wire.

These patterns are labeled "pseudo-Heisenburp", because a true Heisenburp device does not even temporarily damage or affect a passing glider, yet can still produce an output signal in response. However, it is impossible to construct a stable device that can accomplish this for gliders. True stable Heisenburp devices are possible with many other types of spaceships, but not with gliders which have no usable side sparks to initiate an output signal.

:staged recovery A type of signal-processing circuit where the initial reaction between catalysts an incoming signal results in an imperfect recovery -- a catalyst is damaged, destroyed completely as in a bait reaction, or one or more objects are left behind that must be cleaned up before the circuit can be reused. In any of these three cases, output signals from the circuit must be used to complete the cleanup. In theory the cleanup process might itself be dirty, requiring additional cleanup stages. In rare cases this might theoretically allow the construction of special-purpose circuits with a lower recovery time than would otherwise be possible, but in practice this kind of situation does not commonly arise.

An example is the record-breaking (at the time) 487-tick reflector constructed by Adam P. Goucher on 12 April 2009. 487 ticks was a slight improvement over the repeat time of the Silver reflector. The reflector featured a standard Callahan G-to-H, with cleanup by an internal dirty glider reflector found by Dietrich Leithner many years before -- which in turn was cleaned up by the usual ungainly Herschel plumbing attached to the G-to-H's output. The dirty glider reflector is not actually fully recovered before a second p487 signal enters the full reflector. However, it has been repaired by the time the internal reflector is actually needed again, so the cycle can be successfully repeated at p487 instead of p497.

:stairstep hexomino (stabilizes at time 63) The following predecessor of the blockade.

	..OO
	.OO.
	OO..

:stamp collection A collection of oscillators (or perhaps other Life objects) in a single diagram, displaying the exhibits much like stamps in a stamp album. The classic examples are by Dean Hickerson (see http://conwaylife.com/ref/DRH/stamps.html).

:standard spaceship A glider, LWSS, MWSS or HWSS. These have all been known since 1970.

:star (p3) Found by Hartmut Holzwart, February 1993.

	.....O.....
	....OOO....
	..OOO.OOO..
	..O.....O..
	.OO.....OO.
	OO.......OO
	.OO.....OO.
	..O.....O..
	..OOO.OOO..
	....OOO....
	.....O.....

:star gate A device by Dieter Leithner (October 1996) for transporting a LWSS faster than the speed of light. The key reaction is the Fast Forward Force Field.

:stator The cells of an oscillator that are always on. Compare rotor. (The stator is sometimes taken to include also some of those cells which are always off.) The stator is divided into the bushing and the casing.

By analogy, the cells of an eater that remain on even when the eater is eating are considered to constitute the stator of the eater. This is not always well-defined, because an eater can have more than one eating action.

:statorless A statorless oscillator is one in which no cell is permanently on - that is, the stator is empty.

:step Another term for a generation or tick. This term is particularly used in describing conduits. For example, a 64-step conduit is one through which the active object takes 64 generations to pass.

:stillater (p3) Found by Robert Wainwright, September 1985. This is one of only three essentially different p3 oscillators with only three cells in the rotor. The others are 1-2-3 and cuphook.

	...O....
	..O.O.OO
	..O.OO.O
	OO......
	.O.O.OO.
	.O.O..O.
	..O..O..
	...OO...

:still life Any stable pattern, usually assumed to be finite and nonempty. For the purposes of enumerating still lifes this definition is, however, unsatisfactory because, for example, any pair of blocks would count as a still life, and there would therefore be an infinite number of 8-bit still lifes. For this reason a stricter definition is often used, counting a stable pattern as a single still life only if its islands cannot be divided into two nonempty sets both of which are stable in their own right. Compare pseudo still life.

The requirement that a still life not be decomposable into two separate stable patterns may seem a bit arbitrary, as it does not rule out the possibility that it might be decomposable into more than two. This is shown by the patterns in the following diagram, both found by Gabriel Nivasch in July 2001. On the left is a 32-cell pattern that can be broken down into three stable pieces but not into two. On the right is a 34-cell pattern that can be broken down into four stable pieces but not into two or three. (Note that, as a consequence of the Four-Colour Theorem, four is as high as you need ever go.) It is arguable that patterns like these ought not to be considered as single still lifes.

	......OO...........OO.
	..O.O..O......OO.O..O.
	.O.OO.O.......O.OO.O..
	.O....OO...........OO.
	OO.OO.........O.OO...O
	...OO.OO....OOO.OO.OO.
	OO....O....O.......O..
	.O.OO.O.....OOO.OO.O..
	O..O.O........O.O.O...
	OO....................

Still lifes have been enumerated by Conway (4-7 bits), Robert Wainwright (8-10 bits), Dave Buckingham (11-13 bits), Peter Raynham (14 bits) and Mark Niemiec (15-24 bits). The resulting figures are shown below. (These figures shouldn't be affected by the above discussion of the strict definition of "still life", because it is unlikely that there are any doubtful cases with much less than 32 cells.)

	--------------
	Bits    Number
	--------------
	 4           2
	 5           1
	 6           5
	 7           4
	 8           9
	 9          10
	10          25
	11          46
	12         121
	13         240
	14         619
	15        1353
	16        3286
	17        7773
	18       19044
	19       45759
	20      112243
	21      273188
	22      672172
	23     1646147
	24     4051711
	25     9971377
	26    24619307
	27    60823008
	28   150613157
	29   373188952
	30   926068847
	31  2299616637
	32  5716948683
	--------------
All still lifes up to 18 bits have been shown to be glider constructible. It is an open question whether all still lifes can be incrementally constructed using glider collisions. For the subset of small still lifes that have been found to be especially useful in self-constructing circuitry, see also Spartan.

:still life tagalong A tagalong which takes the form of a still life in at least one phase. An example is shown below.

	..OO...............
	.OO.OO.............
	..OOOO.............
	...OO..............
	...................
	...OOOOO...........
	..OOOOOOO..........
	.OO.OOOOO..........
	..OO...............
	...................
	........O.O.....OO.
	......O....O...O..O
	......OO.....O.O..O
	.O..O..OOOO.O...OO.
	O.......OO.........
	O...O..............
	OOOO...............

:stream A line of identical objects (usually spaceships), each of which is moving in the same direction, this direction being parallel to the line. Compare with wave.

:stretcher Any pattern that grows by stretching a wick or agar. See wickstretcher and spacefiller.

:strict volatility A term suggested by Noam Elkies in August 1998 for the proportion of cells involved in a period n oscillator which themselves oscillate with period n. For prime n this is the same as the ordinary volatility.

:super beehive = honeycomb

:superfountain (p4) A p4 sparker which produces a 1-cell spark that is separated from the rest of the oscillator by two clear rows of cells. The first superfountain was found by Noam Elkies in February 1998. In January 2006 Nicolay Beluchenko found the much smaller one shown below. See also fountain.

	...........O...........
	.......................
	.......................
	.....O..O.....O..O.....
	...OO..O.OOOOO.O..OO...
	.....O...........O.....
	...O.OO.........OO.O...
	.O.O...OOO...OOO...O.O.
	OOO.O.............O.OOO
	..........O.O..........
	....OOO...O.O...OOO....
	....O..O...O...O..O....
	...OOOO..O.O.O..OOOO...
	...OO..OOO.O.OOO..OO...
	..O...O...O.O...O...O..
	...O..O.O.O.O.O.O..O...
	....O.O.OO...OO.O.O....
	.....O...........O.....

:superlinear growth Growth faster than any rate proportional to T, where T is the number of ticks that a pattern has been run. This term usually applies to a pattern's population growth -- e.g., breeders' and spacefillers' population asymptotically grows faster than any linear-growth pattern -- rather than diametric growth or bounding-box growth. It may also be used to describe the rate of increase in the number of subpatterns present in a pattern, such as when describing a replicator's rate of reproduction. Due to limits enforced by the speed of light, no pattern's population can grow at an asymptotic rate faster than quadratic growth.

:superstring An infinite orthogonal row of cells stabilized on one side so that it moves at the speed of light, often leaving debris behind. The first examples were found in 1971 by Edward Fitzgerald and Robert Wainwright. Superstrings were studied extensively by Peter Rott during 1992-1994, and he found examples with many different periods. (But no odd periods. In August 1998 Stephen Silver proved that odd-period superstrings are impossible.)

Sometimes a finite section of a superstring can be made to run between two tracks ("waveguides"). This gives a fuse which can be made as wide as desired. The first example was found by Tony Smithurst and uses tubs. (This is shown below. The superstring itself is p4 with a repeating section of width 9 producing one blinker per period and was one of those discovered in 1971. With the track in place, however, the period is 8. This track can also be used with a number of other superstrings.) Shortly after seeing this example, in March 1997 Peter Rott found another superstring track consisting of boats. At present these are the only two waveguides known. Both are destroyed by the superstring as it moves along - it would be interesting to find one that remains intact.

See titanic toroidal traveler for another example of a superstring.

	.OO..........................................................
	O..O...O...O...O...O...O...O...O...O...O...O...O...O...O...O.
	....O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O
	O..O...O...O...O...O...O...O...O...O...O...O...O...O...O...O.
	.OOO.........................................................
	..OO.........................................................
	..OO.........................................................
	...O.........................................................
	...O.........................................................
	...O.........................................................
	...O.........................................................
	...O.........................................................
	...O.........................................................
	...O.........................................................
	..OO.........................................................
	..OO.........................................................
	.OOO.........................................................
	O..O...O...O...O...O...O...O...O...O...O...O...O...O...O...O.
	....O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O
	O..O...O...O...O...O...O...O...O...O...O...O...O...O...O...O.
	.OO..........................................................

:support Those parts of an object which are only present in order to keep the rest of the object (such an engine or an edge spark) working correctly. These can be components of the object, or else accompanying objects used to perturb the object. In many cases there is a wide variation of support possible for an engine. The arms in many puffers are an example of support.

:surprise (p3) Found by Dave Buckingham, November 1972.

	...O....OO
	...OOO..O.
	.OO...O.O.
	O..OO.O.OO
	.O......O.
	OO.O.OO..O
	.O.O...OO.
	.O..OOO...
	OO....O...

:swan (c/4 diagonally, p4) A diagonal spaceship producing some useful sparks. Found by Tim Coe in February 1996.

	.O..........OO..........
	OOOOO......OO...........
	O..OO........O.......OO.
	..OO.O.....OO......OOO.O
	...........OO...O.OO....
	.....O.O......OO........
	..........OOO.O....O....
	.......OOO...O....O.....
	........O.......O.......
	........O......O........
	........................
	...........O............

:swimmer = switch engine.

:swimmer lane = switch engine channel.

:switch A signal-carrying circuit that can be modified so that it cleanly absorbs any future signals instead of allowing them to pass. Optionally there may be a separate mechanism to restore the circuit to its original function.

In the following example, a glider from the northeast (shown) will perform a simple block pull that switches off an F166 conduit, so that any future Herschel inputs will be cleanly absorbed. A glider from the southwest (also shown) can restore the block to its original position.

	.OO........................................................
	..O........................................................
	.O.........................................................
	.OO...............................................OO.......
	...................................................O.......
	..................................................O........
	..................................................OO.......
	..................................O........................
	..................................O.O......................
	O...OO............................OO.......................
	OO..OO.....................................................
	.OO......................OO................................
	OO.......................OO..........................OO....
	.....................................................OO....
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	.............OO............................................
	............O.O........OO..................................
	..............O.......O.O..................................
	......................O....................................
	.....................OO.........................OO.........
	................................................OO.........
	...........................................................
	...........................................................
	..................................OO.....................OO
	...................................O......................O
	................................OOO....................OOO.
	................................O......................O...
	............................................OO.............
	............................................O..............
	.............................................OOO...........
	...............................................O...........

:switchable gun A gun that includes a mechanism to turn the output stream off and on with simple signals, often gliders. A small example is Dietrich Leithner's switchable LWSS gun from July 8, 1995. The ON signal enters from the northeast, and the OFF signal from the northwest:

	.................OO...........................................
	.................O..O.........................................
	..............................................................
	.....................O........................................
	..............................................................
	.O.................OO.........................................
	..O...............O...........................................
	OOO...........................................................
	..............................................................
	...............OO...OO........................................
	...............OO...OO........................................
	................OOOOO........................O................
	.................O.O........................O.................
	............................................OOO...............
	.................OOO..........................................
	....................................O.O.......................
	....................................O...O.....................
	........................................O.......O.............
	..........................OO........O....O....OOOO............
	..........................OO............O....O.O.OO...........
	.....................O..............O...O...O..O.OOO........OO
	......................O.............O.O......O.O.OO.........OO
	....................OOO.......................OOOO............
	................O...............................O.............
	...............OOO...................O........................
	..............OOOOO..................O.O.....O................
	.............OO...OO.................OO....OOO................
	..........................................O...................
	.............................O............OO..................
	...........................O..O.........OOO...................
	...............OOO..........OOO.........OO....................
	...............OOO..........O..........O.O....................
	.............................O................................
	.............................OOO..............................
	................OO............................................
	................OO............................................
	.....................O........................................
	...................OOOO......OO..OO...........................
	.............OO...O.O.OO.....OOOO.O..O.O......................
	.............OO..O..O.OOO.....OO.O...O...O....................
	..................O.O.OO....O............O.....OO.............
	...................OOOO..............O....O....OO.............
	.....................O...................O....................
	.....................................O...O....................
	.....................................O.O......................

:switch engine The following pattern, which in itself is unstable, but which can be used to make c/12 diagonal puffers and spaceships.

	.O.O..
	O.....
	.O..O.
	...OOO

The switch engine was discovered by Charles Corderman in 1971. He also found the two basic types of stabilized switch engine: a p288 block-laying type (the more common of the two) and p384 glider-producing type. These two puffers are the most natural infinite growth patterns in Life, being the only ones ever seen to occur from random starting patterns.

Patterns giving rise to block-laying switch engines can be seen under infinite growth, and one giving rise to a glider-producing switch engine is shown under time bomb. See also Cordership and ark.

:switch engine channel Two lines of boats (or other suitable objects, such as tub with tails) arranged so that a switch engine can travel between them, in the following manner:

	..............OO................
	.............O.O................
	..............O.................
	................................
	................................
	................................
	................................
	................................
	.......OOO............OO........
	........O..O.........O.O........
	............O.........O.........
	.........O.O....................
	................................
	................................
	................................
	................................
	..............................OO
	.............................O.O
	..............................O.
	................................
	................................
	.O..............................
	O.O.............................
	OO..............................
	................................
	................................
	................................
	................................
	................................
	.........O......................
	........O.O.....................
	........OO......................
David Bell used this in June 2005 to construct a "bobsled" oscillator, in which a switch engine factory sends switch engines down a channel, at the other end of which they are deleted.

:switch engine chute = switch engine channel

:switch-engine ping-pong A very large (210515×183739) quadratic growth pattern found by Michael Simkin in October 2014. Currently this is the smallest starting population (23 cells) known to result in a quadratic population growth rate.

:synthesis = glider synthesis

:syringe A small stable glider-to-Herschel converter found by Tanner Jacobi in March 2015. A second glider can safely follow the first any time after 78 ticks, but overclocking also allows the syringe to work at a repeat time of 74 or 75 ticks. If followed by a dependent conduit a simple eater2 can be used instead of the large welded shown here. A ghost Herschel marks the output location.

	....O.............................
	.....O............................
	...OOO............................
	..................O...............
	................OOO...............
	...............O..................
	...............OO.................
	OO................................
	.O................................
	.O.OO.............................
	..O..O.......................O....
	...OO........................O....
	..................OO.........OOO..
	..................OO...........O..
	..................................
	..................................
	..................................
	...........................O...OO.
	..........................O.O...O.
	.........................O.O...O..
	.....................OO.O.O...O...
	.....................OO.O..OOOO.O.
	.........................O.O...O.O
	.....................OO.OO..O..O.O
	......................O.O..OO...O.
	..........OO..........O.O.........
	..........OO...........O..........

:T = T-tetromino

:table The following induction coil.

	OOOO
	O..O

:table on table (p1)

	O..O
	OOOO
	....
	OOOO
	O..O

:tag = tagalong

:tagalong An object which is not a spaceship in its own right, but which can be attached to one or more spaceships to form a larger spaceship. For examples see Canada goose, fly, pushalong, sidecar and sparky. See also Schick engine, which consists of a tagalong attached to two LWSS (or similar).

The following c/4 spaceship (Nicolay Beluchenko, February 2004) has two wings, either of which can be considered as a tagalong. But if either wing is removed, then the remaining wing becomes an essential component of the spaceship, and so is no longer a tagalong.

	.......................O.......................
	.......................O.......................
	......................O.O......................
	...............................................
	.....................O...O.....................
	....................OO...OO....................
	..................OO.O...O.OO..................
	................OO.O.O...O.O.OO................
	............O...OOO.O.....O.OOO...O............
	............OOOOOO...........OOOOOO............
	...........O..O....O.......O....O..O...........
	...................O.......O...................
	..........OOO.....................OOO..........
	.........O.OO.....................OO.O.........
	........O..O.......................O..O........
	........O.............................O........
	.........OO.........................OO.........
	.........OO.........................OO.........
	OOO......O...........................O......OOO
	.O......OOO.........................OOO......O.
	......OO..O.........................O..OO......
	..OO.O.OOO...........................OOO.O.OO..
	.O...O.O...............................O.O...O.
	.O...OO.................................OO...O.

:tail spark A spark at the back of a spaceship. For example, the 1-bit spark at the back of a LWSS, MWSS or HWSS in their less dense phases.

:tame To perturb a dirty reaction using other patterns so as to make it clean and hopefully useful. Or to make a reaction work which would otherwise fail due to unwanted products which interfere with the reaction.

:taming See tame.

:tandem glider Two synchronized gliders traveling at a fixed spacetime offset, usually as a single signal in a Herschel transceiver. See also glider pair.

:target A necessary component of a slow salvo recipe used by a single-arm universal constructor. A target usually consists of a single object, or sometimes a small constellation of common still lifes and/or oscillators. See intermediate target. If no hand target is available, a construction arm may be unable to construct anything, unless recipes are available to generate targets directly from the elbow.

:teardrop The following induction coil, or the formation of two beehives that it evolves into after 20 generations. (Compare butterfly, where the beehives are five cells further apart.)

	OOO.
	O..O
	O..O
	.OO.

:technician (p5) Found by Dave Buckingham, January 1973.

	.....O.....
	....O.O....
	....OO.....
	..OO.......
	.O...OOO...
	O..OO...O.O
	.OO....O.OO
	...O.O.O...
	...O...O...
	....OOO....
	......O.O..
	.......OO..

:technician finished product = technician

:tee A head-on collision between three gliders, producing a perpendicular output glider that can be used to construct closely spaced glider salvos. There are several workable recipes. One of the more useful is the following, because the tandem glider can be generated by a small Herschel converter:

	...............O.
	..............O..
	..............OOO
	.........O.......
	.........O.O.....
	.........OO......
	.OO..............
	O.O..............
	..O..............

:teeth A 65-cell quadratic growth pattern found by Nick Gotts in March 2000. This (and a related 65-cell pattern which Gotts found at about the same time) beat the record previously held by mosquito5 for smallest population known to have superlinear growth. Now superseded by catacryst, metacatacryst, Gotts dots and wedge.

:telegraph A pattern created by Jason Summers in February 2003. It transmits and receives information using a beehive-chain lightspeed wire -- a rare type of reburnable fuse -- at the rate of 1440 ticks per bit. The rate of travel of signals through the entire transceiver device can be increased to any speed strictly less than the speed of light by increasing the length of the chain of beehives appropriately.

"Telegraph" may also refer to any device that sends and receives lightspeed signals; see also p1 telegraph, high-bandwidth telegraph.

:ternary reaction Any reaction between three objects. In particular, a reaction in which two gliders from one stream and one glider from a crossing stream of the same period annihilate each other. This can be used to combine two glider guns of the same period to produce a new glider gun with double the period.

:test tube baby (p2)

	OO....OO
	O.O..O.O
	..O..O..
	..O..O..
	...OO...

:tetraplet Any 4-cell polyplet.

:tetromino Any 4-cell polyomino. There are five such objects, shown below. The first is the block, the second is the T-tetromino and the remaining three rapidly evolve into beehives.

	OO......OOO......OOOO......OOO......OO.
	OO.......O...................O.......OO

:The Online Life-Like CA Soup Search A distributed search effort set up by Nathaniel Johnston in 2009, using a Python script running in Golly. Results included a collection of the longest-lived 20×20 soups, as well as a census of over 174 billion ash objects. It has since been superseded by Catagolue.

:The Recursive Universe A popular science book by William Poundstone (1985) dealing with the nature of the universe, illuminated by parallels with the game of Life. This book brought to a wider audience many of the results that first appeared in LifeLine. It also outlines the proof of the existence of a universal constructor in Life first given in Winning Ways.

:thumb A spark-like protrusion which flicks out in a manner resembling a thumb being flicked. Below on the left is a p9 thumb sparker found by Dean Hickerson in October 1998. On the right is a p4 example found by David Eppstein in June 2000.

	.......O..............O.....
	...OO...O.........OO...O....
	...O.....O.OO.....O.....O...
	OO.O.O......O......OOO.O.OO.
	OO.O.OO.OOOO............OO.O
	...O.O...........OOOOOO....O
	...O.O.OOO.......O....OOOOO.
	....O.O...O.........O.......
	......O..OO........O.OOOO...
	......OO...........O.O..O...
	....................O.......

:thunderbird (stabilizes at time 243)

	OOO
	...
	.O.
	.O.
	.O.

:tick = generation

:tie A term used in naming certain still lifes (and the stator part of certain oscillators). It indicates that the object consists of two smaller objects joined point to point, as in ship tie boat.

:time bomb The following pattern by Doug Petrie, which is really just a glider-producing switch engine in disguise. See infinite growth for some better examples of a similar nature.

	.O...........OO
	O.O....O......O
	.......O....O..
	..O..O...O..O..
	..OO......O....
	...O...........

:titanic toroidal traveler The superstring with the following repeating segment. The front part becomes p16, but the eventual fate of the detached back part is unknown.

	OOOOOO
	OOO...

:TL = traffic light

:T-nosed p4 (p4) Found by Robert Wainwright in October 1989. See also filter.

	.....O.....
	.....O.....
	....OOO....
	...........
	...........
	...........
	...OOOOO...
	..O.OOO.O..
	..O.O.O.O..
	.OO.O.O.OO.
	O..OO.OO..O
	OO.......OO

:T-nosed p5 (p5) Found by Nicolay Beluchenko in April 2005.

	.....OO...............OO.OO.....O........
	..O..O.........OO.O.OOO.OO......O........
	.O.O.O.....O....O.O.OOO......OO.O........
	O..O.O.OOOOOO.....O....O.O...OO.O........
	.OO.O.O..O...OOO..O.OOOO..O.O.OO.OO......
	..O.O..OO.O..O..O.OO....OOO.O.O....OO....
	.O..O...O..O.O.OO....OOO...O.............
	.O.O.O...OOO.O...OOOO...O..O.O..OO.O..O..
	OO.O.........OO.O....O.O.O.O........O.OOO
	.O.O.O...OOO.O...OOOO...O..O.O..OO.O..O..
	.O..O...O..O.O.OO....OOO...O.............
	..O.O..OO.O..O..O.OO....OOO.O.O....OO....
	.OO.O.O..O...OOO..O.OOOO..O.O.OO.OO......
	O..O.O.OOOOOO.....O....O.O...OO.O........
	.O.O.O.....O....O.O.OOO......OO.O........
	..O..O.........OO.O.OOO.OO......O........
	.....OO...............OO.OO.....O........

:T-nosed p6 (p6) Found by Achim Flammenkamp in September 1994. There is also a much larger and fully symmetric version found by Flammenkamp in August 1994.

	......OO...OO......
	......O.O.O.O......
	.......O...O.......
	...................
	..O.O.O.....O.O.O..
	OOO.O.OO...OO.O.OOO
	..O.O.O.....O.O.O..
	...................
	.......O...O.......
	......O.O.O.O......
	......OO...OO......

:toad (p2) Found by Simon Norton, May 1970. This is the second most common oscillator, although blinkers are more than a hundred times as frequent. See also killer toads.

	.OOO
	OOO.

:toad-flipper A toad hassler that works in the manner of the following example. Two domino sparkers, here pentadecathlons, apply their sparks to the toad in order to flip it over. When the sparks are applied again it is flipped back. Either or both domino sparkers can be moved down two spaces from the position shown and the toad-flipper will still work, but because of symmetry there are really only two different types. Compare toad-sucker.

	.O..............O.
	.O..............O.
	O.O............O.O
	.O..............O.
	.O......O.......O.
	.O......OO......O.
	.O......OO......O.
	O.O......O.....O.O
	.O..............O.
	.O..............O.

:toad-sucker A toad hassler that works in the manner of the following example. Two domino sparkers, here pentadecathlons, apply their sparks to the toad in order to shift it. When the sparks are applied again it is shifted back. Either or both domino sparkers can be moved down two spaces from the position shown and the toad-sucker will still work, but because of symmetry there are really only three different types. Compare toad-flipper.

	.O................
	.O..............O.
	O.O.............O.
	.O.............O.O
	.O......O.......O.
	.O......OO......O.
	.O......OO......O.
	O.O......O......O.
	.O.............O.O
	.O..............O.
	................O.

:toaster (p5) Found by Dean Hickerson, April 1992.

	....O......OO..
	...O.O.OO..O...
	...O.O.O.O.O...
	..OO.O...O.OO..
	O...OO.O.OO...O
	...O.......O...
	...O.......O...
	O...OO.O.OO...O
	..OO.O...O.OO..
	...O.O.O.O.O...
	...O.O.OO..O...
	....O......OO..

:toggleable gun Any gun that can be turned off or turned on by the same external signal -- the simplest possible switching mechanism. An input signal causes the gun to stop producing gliders. Another input signal from the same source restores the gun to its original function. Compare switchable gun.

Here's a small example by Dean Hickerson from September 1996:

	..............OO..............O..
	..............O.O.............O.O
	..............O...............OO.
	.................................
	.................................
	.................................
	.................................
	...............O..O....b.........
	.OOOO..............O..b..........
	O...O..........O...O..bbb........
	....O...........OOOO.............
	O..O........................aaa..
	............................a....
	.............................a...
In the figure above, glider B and an LWSS are about to send a glider NW. Glider A will delete the next glider after B, turning off the output stream. But if the device were already off, B wouldn't be present and A would instead delete the leading LWSS, turning the device back on.

:toggle circuit Any signal-processing circuit that switches back and forth between two possible states or outputs . An example is the following alternating H-to-G converter:

	............O.....................................O........
	...........O.O...................................O.O.......
	............O.....................................O........
	...........................................................
	..........OOOOO.................................OOOOO......
	..........O....O................................O....O.....
	.............O..O..................................O..O....
	.............OO.O..O...............................OO.O..O.
	..........O.....O.O.O...........................O.....O.O.O
	.........O.O....O..O...........................O.O....O..O.
	.........O..O..OO..............................O..O..OO....
	..........OO....................................OO.........
	...........................................................
	...........................................................
	...........................................................
	.............................................OO............
	.............................................OO............
	...........................................................
	...........................................................
	...........................................................
	OO....................................OO...................
	OO....................................OO...................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	.........OO....................................OO..........
	.........OO....................................OO..........
	...........................................................
	OO.O.......O..........................OO.O.......O.........
	O.OO......OOO.........................O.OO......OOO........
	.........OO..O.................................OO..O.......

:TOLLCASS Acronym for The Online Life-Like CA Soup Search.

:toolkit A set of Life reactions and mechanisms that can be used to solve any problem in a specific pre-defined class of problems -- glider timing adjustment, salvo creation, seed construction, etc. See also universal toolkit.

:torus As applies to Life, usually means a finite Life universe which takes the form of an m × n rectangle with the bottom edge considered to be joined to the top edge and the left edge joined to the right edge, so that the universe is topologically a torus. There are also other less obvious ways of obtaining an toroidal universe.

See also Klein bottle.

:total aperiodic Any finite pattern which evolves in such a way that no cell in the Life plane is eventually periodic. The first example was found by Bill Gosper in November 1997. A few days later he found the following much smaller example consisting of three copies of a p12 backrake by Dave Buckingham.

	.........................................O.................
	........................................OOO................
	.......................................OO.O.....O..........
	.......................................OOO.....OOO.........
	........................................OO....O..OO...OOO..
	..............................................OOO....O..O..
	........................................................O..
	........................................................O..
	........................................................O..
	........................................OOO............O...
	........................................O..O...............
	........................................O..................
	........................................O..................
	.........................................O.................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	...........................................................
	......................................OOO..................
	......................................O..O...........O.....
	......................................O.............OOO....
	......................................O............OO.O....
	......................................O............OOO.....
	.......................................O............OO.....
	...........................................................
	...........................................................
	...................................OOO.....................
	..................................OOOOO....................
	..................................OOO.OO.......OO........O.
	.....................................OO.......OOOO........O
	..............................................OO.OO...O...O
	................................................OO.....OOOO
	...........................................................
	...........................................................
	....................O......................................
	.....................O.....................................
	.OO.............O....O................................OOO..
	OOOO.............OOOOO..................................O..
	OO.OO...................................................O..
	..OO...................................................O...
	....................................O......................
	.....................................O.....................
	.....................OO..........O...O.....................
	......................OO..........OOOO...............OO....
	.....................OO...........................OOO.OO...
	.....................O............................OOOOO....
	...................................................OOO.....
	...........................................................
	......................OO...................................
	.............OOOO....OOOO..................................
	............O...O....OO.OO.................................
	.OOOOO..........O......OO..................................
	O....O.........O...........................................
	.....O.....................................................
	....O......................................................

:T-pentomino Conway's name for the following pentomino, which is a common parent of the T-tetromino.

	OOO
	.O.
	.O.

:track A path made out of conduits, often ending where it begins so that the active signal object is cycled forever, forming an oscillator or a gun.

This term has also been used to refer to the lane on which a glider or spaceship travels. The concept is very similar, but a reference to a "track" now usually implies a non-trivial supporting conduit.

:tractor beam A stream of spaceships that can draw an object towards the source of the stream. The example below shows a tractor beam pulling a loaf; this was used by Dean Hickerson to construct a sawtooth.

	.....................O..O......................
	.....OOOO...........O..............OOOO........
	.....O...O..........O...O..........O...O.......
	.....O........OO....OOOO...........O........OO.
	.OO...O..O...OOOO...........OO......O..O...OOOO
	O..O........OO.OO..........OO.OO..........OO.OO
	O.O..........OO.............OOOO...........OO..
	.O...........................OO................

:traffic circle (p100)

	.....................OO....OO...................
	.....................O.O..O.O...................
	.......................O..O.....................
	......................OO..OO....................
	.....................OOO..OOO...................
	.......................O..O.....................
	...............................O................
	..............................O.OO..............
	..................................O.............
	..........................O...O..O.O............
	..........................O.....O..O............
	..........................O......OO.............
	.........OO.....................................
	........O..O..........OOO...OOO.................
	.......O.O.O....................................
	......OOO.O...............O.....................
	......OOO.................O.....................
	..........................O.....................
	............OOO.................................
	OO..O................OOO........................
	O..OO.....O.....O...............................
	.OOOOO....O.....O..O.....O.................O..OO
	..........O.....O..O.....O.................OO..O
	...................O.....O.......OOO......OOOOO.
	.OOOOO......OOO.................................
	O..OO................OOO.......O.....O..........
	OO..O..........................O.....O....OOOOO.
	...............................O.....O.....OO..O
	...........................................O..OO
	.................................OOO............
	.......................................OO.......
	......................................OOO.......
	.....................................O.OO.......
	....................................O.O.........
	....................OOO.............O..O........
	.....................................OO.........
	.............OO....O..O.........................
	............O..O................................
	............O.O.O...............................
	.............O..O...............................
	.................O..............................
	..............O.O...............................
	.....................O..O.......................
	...................OOO..OOO.....................
	....................OO..OO......................
	.....................O..O.......................
	...................O.O..O.O.....................
	...................OO....OO.....................

:traffic jam Any traffic light hassler, such as traffic circle. The term is also applied to the following reaction, used in most traffic light hasslers, in which two traffic lights interact in such a way as to reappear after 25 generations with an extra 6 spaces between them.

	..OOO...........
	...........OOO..
	O.....O.........
	O.....O..O.....O
	O.....O..O.....O
	.........O.....O
	..OOO...........
	...........OOO..

:traffic light (p2) A common formation of four blinkers.

	..OOO..
	.......
	O.....O
	O.....O
	O.....O
	.......
	..OOO..

:traffic lights extruder A growing pattern constructed by Jason Summers in October 2006, which slowly creates an outward-growing chain of traffic lights. The growth occurs in waves which travel through the chain from one end to the other. It can be thought of as a complex fencepost for a wick that does not need a wickstretcher.

The following illustrates the reaction used, in which a newly created traffic light at the left eventually pushes the rightmost one slightly to the right.

	......................O.......................O....
	......................O.......................O....
	.........OOO..........O..........OOO..........O....
	.OO................................................
	OOO....O.....O....OOO...OOO....O.....O....OOO...OOO
	.OO....O.....O.................O.....O.............
	.......O.....O........O........O.....O........O....
	......................O.......................O....
	.........OOO..........O..........OOO..........O....

:trans-beacon on table (p2)

	....OO
	.....O
	..O...
	..OO..
	......
	OOOO..
	O..O..

:trans-boat with tail (p1)

	OO...
	O.O..
	.O.O.
	...O.
	...OO

:transceiver = Herschel transceiver.

:trans-loaf with tail (p1)

	.O....
	O.O...
	O..O..
	.OO.O.
	....O.
	....OO

:transmitter = Herschel transmitter.

:transparent In signal circuitry, a term used for a catalyst that is completely destroyed by the passing signal, then rebuilt. Often (though not always) the active reaction passes directly through the area occupied by the transparent catalyst, then rebuilds the catalyst behind itself, as in the transparent block reaction. See also transparent lane.

:transparent block reaction A certain reaction between a block and a Herschel predecessor in which the block reappears in its original place some time later, the reaction having effectively passed through it. This reaction was found by Dave Buckingham in 1988. It has been used in some Herschel conduits, and in the gunstars. Because the reaction involves a Herschel predecessor rather than an actual Herschel, the following diagram shows instead a B-heptomino (which by itself would evolve into a block and a Herschel).

	O.............
	OO..........OO
	.OO.........OO
	OO............

:transparent debris effect A reaction in which a Herschel or other active region destroys a still life, then later, having passed through the place where the still life was, recreates the still life in its original position. For an example, see transparent block reaction.

:transparent lane A path through a signal-producing circuit that can be used to merge signal streams. The signal -- usually a standard spaceship such as a glider -- can either be produced by the circuit, or it can come from elsewhere, passing safely through on the transparent lane without interacting with the circuit.

:trice tongs (p3) Found by Robert Wainwright, February 1982. In terms of its 7×7 bounding box this ties with jam as the smallest p3 oscillator.

	..O....
	..OOO..
	OO...O.
	.O.O.O.
	.O.....
	..OO..O
	.....OO

:trigger A signal, usually a single glider, that collides with a seed constellation to produce a relatively rare still life or oscillator, or an output spaceship or other signal. The constellation is destroyed or damaged in the process; compare circuit, reflector. Here a pair of trigger gliders strike a dirty seed constellation assembled by Chris Cain in March 2015, to launch a three-engine Cordership:

	....................................................OO.
	................................................OO..OO.
	................................................OO.....
	.......................................................
	.......................................................
	.......................................................
	........................................OO.............
	........................................OO.............
	...................................................OO..
	..................................O................O.O.
	.................................O.O...........OO...O.O
	..................................OO..........O.O....O.
	...............................................O.......
	.......................................................
	..................................O.................OOO
	.................................O.O................O..
	..................................OO.................O.
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	...........................O...........................
	..........................O.O..........................
	...........................OO..........................
	.......................................................
	.......................................................
	...........................O...........................
	..........................O.O..........................
	...........................OO..........................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	.......O....O..........................................
	......O.O..O.O.........................................
	.......OO...OO.........................................
	.......................................................
	.......................................................
	.......................................................
	.......................................................
	OO.....................................................
	O.O....................................................
	.O.O...................................................
	..O....................................................
	.......................................................
	.......................................................
	.......................................................
	.............O.........................................
	............OO.........................................
	............O.O........................................

:triomino Either of the two 3-cell polyominoes. The term is rarely used in Life, since the two objects in question are simply the blinker and the pre-block.

:triple caterer (p3) Found by Dean Hickerson, October 1989. Compare caterer and double caterer.

	.....OO.........
	....O..O..OO....
	....OO.O...O....
	......O.OOO....O
	..OOO.O.O....OOO
	.O..O..O....O...
	O.O..O...O..OO..
	.O..............
	..OO.OO.OO.OO...
	...O...O...O....
	...O...O...O....

:triplet Any 3-cell polyplet. There are 5 such objects, shown below. The first two are the two triominoes, and the other three vanish in two generations.

	O..................O.......O.......O..
	OO......OOO......OO.......O.O.......O.
	.....................................O

:tripole (p2) The barberpole of length 3.

	OO....
	O.O...
	......
	..O.O.
	.....O
	....OO

:tritoad (p3) Found by Dave Buckingham, October 1977.

	.........OO.......
	.........O........
	..........O..OO...
	.......OOO.O..O...
	......O....OO.O.OO
	......O.OO..O.O.OO
	...OO.O...OO..O...
	...O..OO...O.OO...
	OO.O.O..OO.O......
	OO.O.OO....O......
	...O..O.OOO.......
	...OO..O..........
	........O.........
	.......OO.........

:trivial A trivial period-N oscillator is one in which every cell oscillates at some smaller factor of N. See omniperiodic.

:true Opposite of pseudo. A gun emitting a period n stream of spaceships (or rakes) is said to be a true period n gun if its mechanism oscillates with period n. (The same distinction between true and pseudo also exists for puffers.) True period n guns are known to exist for all periods greater than 61 (see My Experience with B-heptominos in Oscillators), but only a few smaller periods have been achieved, namely 20, 22, 24, 30, 36, 40, 44, 45, 46, 48, 50, 54, 55, 56, 59 and 60. (Credits for these small period guns are: p30, p46 and p60 by Bill Gosper in 1970-1971, p44 by Dave Buckingham in 1992, p50 by Dean Hickerson in 1996, p24 and p48 by Noam Elkies in 1997, p54 and p56 by Dieter Leithner in early 1998, p55 by Stephen Silver in late 1998, p22 by David Eppstein in 2000, p36 by Jason Summers in 2004, p59 in 2009 by Adam P. Goucher, p45 in 2010 by Matthias Merzenich, and p20 and p40 in 2013 also by Merzenich.)

The following diagram shows the p22 gun (David Eppstein, August 2000, using two copies of a p22 oscillator found earlier the same day by Jason Summers).

	..................OO.........................
	...................O.......O.................
	...................O.O..............OO.......
	....................OO............OO..O......
	........................OOO.......OO.OO......
	........................OO.OO.......OOO......
	........................O..OO............OO..
	.........................OO..............O.O.
	...................................O.......O.
	...........................................OO
	.............................................
	OO.......................O...................
	.O.....................O.O...................
	.O.O.............OOO....OO...................
	..OO...O........O...O........................
	......O.OO......O....O.......................
	.....O....O......OO.O.........O..............
	......O...O........O...OO......O.............
	.......OOO.............O.O...OOO.............
	.........................O...................
	.........................OO..................

:T-tetromino The following common predecessor of a traffic light.

	OOO
	.O.

:tub (p1)

	.O.
	O.O
	.O.

:tubber (p3) Found by Robert Wainwright before June 1972.

	....O.O......
	....OO.O.....
	.......OOO...
	....OO....O..
	OO.O..OO..O..
	.O.O....O.OO.
	O...O...O...O
	.OO.O....O.O.
	..O..OO..O.OO
	..O....OO....
	...OOO.......
	.....O.OO....
	......O.O....

:tubeater A pattern that consumes the output of a tubstretcher. The smallest known tubeater was found by Nicolay Beluchenko (September 2005), and is shown below in conjunction with the smallest known tubstretcher.

	........O....................
	.......OO....................
	.......O.O...................
	.............................
	..........OO.................
	..........OO.................
	.......................OOO...
	.O......OO...O.........O.....
	OO.....O..O.O.O.........O....
	O.O...OO.O...O.O..........OOO
	....O.........O.O............
	...O...........O.O.....OO....
	...O..O.........O.O....O.O.O.
	.................O.O...O...OO
	..................O.....O....
	...................O..OO..O..
	.....................O.OOOO..
	......................OOO...O
	..........................OO.
	...........................O.
	...........................OO
	..........................O..
	...........................OO

:tubstretcher Any wickstretcher in which the wick is two diagonal lines of cells forming, successively, a tub, a barge, a long barge, etc. The first one was found by Hartmut Holzwart in June 1993, although at the time this was considered to be a boatstretcher (as it was shown with an extra cell, making the tub into a boat). The following small example is by Nicolay Beluchenko (August 2005), using a quarter.

	.......OOO.....
	.......O.......
	........O......
	..........OO...
	...........O...
	...............
	........OO...O.
	OOO.....OO..O.O
	O......O.O...O.
	.O....OO.......
	...OOOO.O......
	....OO.........

:tub with tail (p1) The following 8-cell still life. See eater for a use of this object.

	.O...
	O.O..
	.O.O.
	...O.
	...OO

:tugalong = tagalong

:tumbler (p14) The smallest known p14 oscillator. Found by George Collins in 1970.

	.O.....O.
	O.O...O.O
	O..O.O..O
	..O...O..
	..OO.OO..

:tumbling T-tetson (p8) A T-tetromino hassled by two figure-8s. Found by Robert Wainwright.

	.OOO.................
	O..................OO
	O...O............O.OO
	O..O.O..........O....
	..O.O..O...........O.
	...O...O.......OO.O..
	.......O.......OO....
	....OOO....O.........
	.........OO..........
	...........O.........

:Turing machine See universal computer.

:turner A one-time glider reflector, or in other words a single-glider seed (the term is seldom or never used in relation to spaceships other than gliders). One-time turners may be 90-degree or 180-degree, or they may be 0-degree with the output in the same direction as the input. A reusable turner would instead be called a reflector.

:turning toads (p4 wick) Found by Dean Hickerson, October 1989.

	..............OO.....OO.....OO.....OO.....OO..............
	.......O.....O......O......O......O......O................
	......OO...O....O.O....O.O....O.O....O.O....O.O.O.OO......
	..OO.O.OOO.O..OO..O..OO..O..OO..O..OO..O..OO..O..O..O.OO..
	O..O.OO.........................................OOOOO.O..O
	OO.O..............................................OO..O.OO
	...O..................................................O...
	...OO................................................OO...

:turtle (c/3 orthogonally, p3) Found by Dean Hickerson.

	.OOO.......O
	.OO..O.OO.OO
	...OOO....O.
	.O..O.O...O.
	O....O....O.
	O....O....O.
	.O..O.O...O.
	...OOO....O.
	.OO..O.OO.OO
	.OOO.......O

:twin bees shuttle (p46) Found by Bill Gosper in 1971, this is the basis of all known p46 oscillators, and so of all known true p46 guns (see new gun for an example). There are numerous ways to stabilize the ends, two of which are shown in the diagram. On the left is David Bell's double block reaction (which results in a shorter, but wider, shuttle than usual), and on the right is the stabilization by a single block. This latter method produces a very large spark which is useful in a number of ways (see, for example, metamorphosis). Adding a symmetrically placed block below this one suppresses the spark. See also p54 shuttle.

	.OO........................
	.OO........................
	...........................
	...............O...........
	OO.............OO........OO
	OO..............OO.......OO
	...........OO..OO..........
	...........................
	...........................
	...........................
	...........OO..OO..........
	OO..............OO.........
	OO.............OO..........
	...............O...........
	...........................
	.OO........................
	.OO........................

:twinhat (p1) See also hat and sesquihat.

	..O...O..
	.O.O.O.O.
	.O.O.O.O.
	OO.O.O.OO
	....O....

:twin peaks = twinhat

:twirling T-tetsons II (p60) Found by Robert Wainwright. This is a pre-pulsar hassled by killer toads.

	.......OO...OO..........
	......O.......O.........
	.........O.O............
	.......OO...OO..........
	........................
	........................
	........................
	.....................OOO
	....................OOO.
	.............O..........
	OOO.........OOO.........
	.OOO....................
	....................OOO.
	.....................OOO
	........................
	.OOO....................
	OOO.........OOO.........
	.............O..........
	........................
	........................
	..........OO...OO.......
	............O.O.........
	.........O.......O......
	..........OO...OO.......

:TWIT = tub with tail

:two-arm The type of universal constructor exemplified by the original Gemini spaceship, where two independently programmed construction arms sent gliders in pairs on 90-degree paths to collide with each other at the construction site. Construction recipes for two-arm constructors are much more efficient in general, but they require many more circuits and multiple independent data streams, which both tend to increase the complexity of self-constructing circuitry. Compare single-arm.

:two eaters (p3) Found by Bill Gosper, September 1971.

	OO.......
	.O.......
	.O.O.....
	..OO.....
	.....OO..
	.....O.O.
	.......O.
	.......OO

:two pulsar quadrants (p3) Found by Dave Buckingham, July 1973. Compare pulsar quadrant.

	....O....
	....O....
	...OO....
	..O......
	O..O..OOO
	O...O.O..
	O....O...
	.........
	..OOO....

:UC = universal constructor.

:underpopulation Death of a cell caused by it having fewer than two neighbours. See also overpopulation.

:unit cell See metacell.

:unit Life cell A rectangular pattern, of size greater than 1×1, that can simulate Life in the following sense. The pattern by itself represents a dead Life cell, and some other pattern represents a live Life cell. When the plane is tiled by these two patterns (which then represent the state of a whole Life universe) they evolve, after a fixed amount of time, into another tiling of the plane by the same two patterns which correctly represents the Life generation following the one they initially represented. It is usual to use capital letters for the simulated things, so, for example, for the first known unit Life cell (constructed by David Bell in January 1996), one Generation is 5760 generations, and one Cell is 500×500 cells.

In December 2005, Jason Summers constructed an analogous unit cell for Wolfram's Rule 110, a one-dimensional cellular automaton that is known be universal.

:universal See universal computer, universal constructor, universal toolkit.

:universal computer A computer that can compute anything that is computable. (The concept of computability can be defined in terms of Turing machines, or by Church's lambda calculus, or by a number of other methods, all of which can be shown to lead to equivalent definitions.) The relevance of this to Life is that both Bill Gosper and John Conway proved early on that it is possible to construct a universal computer in the Life universe. (To prove the universality of a cellular automaton with simple rules was in fact Conway's aim in Life right from the start.) Conway's proof is outlined in Winning Ways, and also in The Recursive Universe.

Until recently, no universal Life computer had ever been built in practice In April 2000, Paul Rendell completed a Turing machine construction (see http://rendell-attic.org/gol/tm.htm for details). This, however, has a finite tape, as opposed to the infinite tape of a true Turing machine, and is therefore not a universal computer. But in November 2002, Paul Chapman announced the construction of a universal computer, see http://www.igblan.free-online.co.uk/igblan/ca/. This is a universal register machine based around Dean Hickerson's sliding block memory.

In 2009 Adam P. Goucher constructed a programmable Spartan universal computer/constructor pattern using stable Herschel circuitry. It included memory tapes and registers capable of holding a simple universal instruction set and program data, and also a minimal single-arm universal constructor. Its size meant that it was extremely impractical to program it to be self-constructing, though this was theoretically possible -- at least if the escape of large numbers of gliders could be allowed as a side effect.

In February 2010, Paul Rendell completed a universal Turing machine design with an unlimited tape, as described in his thesis at http://eprints.uwe.ac.uk/22323/1/thesis.pdf.

In 2016 Nicolas Loizeau ("Coban") completed a Life pattern emulating a complete 8-bit programmable computer.

See also universal constructor.

:universal constructor A pattern that is capable of constructing almost any pattern that has a glider synthesis. This definition is a bit vague. A precise definition seems impossible because it has not been proved that all possible glider fleets are constructible. In any case, a universal constructor ought to be able to construct itself in order to qualify as such. An outline of Conway's proof that such a pattern exists can be found in Winning Ways, and also in The Recursive Universe. The key mechanism for the production of gliders with any given path and timing is known as side-tracking, and is based on the kickback reaction. A universal constructor designed in this way can also function as a universal destructor - it can delete almost any pattern that can be deleted by gliders.

In May 2004, Paul Chapman and Dave Greene produced a prototype programmable universal constructor. This is able to construct objects by means of slow glider constructions. It likely that it could be programmed to be construct itself, but the necessary program would be very large; moreover an additional mechanism would be needed in order to copy the program.

A universal constructor is most useful when attached to a universal computer, which can be programmed to control the constructor to produce the desired pattern of gliders. In what follows I will assume that a universal constructor always includes this computer.

The existence of a universal constructor/destructor has a number of theoretical consequences.

For example, the constructor could be programmed to make copies of itself. This is a replicator.

The constructor could even be programmed to make just one copy of itself translated by a certain amount and then delete itself. This would be a (very large, very high period) spaceship. Any translation is possible (except that it must not be too small), so that the spaceship could travel in any direction. It could also travel slower than any given speed, since we could program it to perform some time-wasting task (such as repeatedly constructing and deleting a block) before copying itself. Of course, we could also choose for it to leave some debris behind, thus making a puffer.

It is also possible to show that the existence of a universal constructor implies the existence of a stable reflector. This proof is not so easy, however, and is no longer of much significance now that explicit examples of such reflectors are known.

Progressively smaller universal-constructor mechanisms have been used in the linear propagator, spiral growth pattern, and the Demonoids and Orthogonoid.

Another strange consequence of the existence of universal constructors was pointed out by Adam P. Goucher in 2015. Any glider-constructible pattern, no matter how large, can be constructed with a fixed number of gliders, probably less than ten thousand. This can be done by working out a construction recipe for some type of sliding block memory with a faraway block, attached to a universal constructor. The block's position encodes an integer value that can be processed to retrieve as many bits of information as are needed to build a :1G seed:. Eventually, after a completely unreasonable number of ticks, the seed can be triggered to produce glider salvos which interact to construct the actual target object, after sending a self-destruct signal to the sliding block memory unit.

:universal destructor See universal constructor.

:universal register machine = URM

:universal regulator A regulator in which the incoming gliders are aligned to period 1, that is, they have arbitrary timing (subject to some minimum time required for the regulator to recover from the previous glider).

Paul Chapman constructed the first universal regulator in March 2003. It is adjustable, so that the output can be aligned to any desired period. A stable universal regulator was constructed by Dave Greene in September 2015, with a minimum delay between test signals of 1177 ticks. This provides a possible way for two complex circuits to interact safely, even if they have different base periods -- e.g., to allow signals from a stable logic circuit to be processed by a period-30 mechanism.

:universal toolkit A set of Life reactions and mechanisms that can be used to construct any object that can be constructed by glider collisions.

:unix (p6) Two blocks eating a long barge. This is a useful sparker, found by Dave Buckingham in February 1976. The name derives from the fact that it was for some time the mascot of the Unix lab of the mathematics faculty at the University of Waterloo.

	.OO.....
	.OO.....
	........
	.O......
	O.O.....
	O..O..OO
	....O.OO
	..OO....

:up boat with tail = trans-boat with tail

:U-pentomino Conway's name for the following pentomino, which rapidly dies.

	O.O
	OOO

:URM A universal register machine, particularly Paul Chapman's Life implementation of such a machine. See universal computer for more information.

:vacuum Empty space. That is, space containing only dead cells.

:Venetian blinds The p2 agar obtained by using the pattern O..O to tile the plane. Period 2 stabilizations of finite patches of this agar are known.

	..................O.OO.OO......O......OO.OO.O..................
	..................OO.O.O...OO.O.O.OO...O.O.OO..................
	.....................O...O..O.O.O.O..O...O.....................
	.....................O..OOO...O.O...OOO..O.....................
	....................OO.O.....O.O.O.....O.OO....................
	.......................O..OO.O...O.OO..O.......................
	....................OO..OOO..OO.OO..OOO..OO....................
	................OO.O.OO...OO.OOOOO.OO...OO.O.OO................
	................OO.OO....O...........O....OO.OO................
	...................O..OO.O.O.......O.O.OO..O...................
	................OO..OOO..OO.OOOOOOO.OO..OOO..OO................
	........OO..OO.O.OO...OO.OOOOOOOOOOOOO.OO...OO.O.OO..OO........
	.....O..O...OO.OO....O...................O....OO.OO...O..O.....
	....O.O.O......O..OO.O.O...............O.O.OO..O......O.O.O....
	...O..O.OO..OO..OOO..OO.OOOOOOOOOOOOOOO.OO..OOO..OO..OO.O..O...
	...O.OO....O.OO...OO.OOOOOOOOOOOOOOOOOOOOO.OO...OO.O....OO.O...
	OO.OO...OO.OO....O...........................O....OO.OO...OO.OO
	O.O...OO.O.O..OO.O.O.......................O.O.OO..O.O.OO...O.O
	..O.OO.O.O..OOO..OO.OOOOOOOOOOOOOOOOOOOOOOO.OO..OOO..O.O.OO.O..
	..O.O..OOOO...OO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OO...OOOO..O.O..
	.OO..O.......O...................................O.......O..OO.
	O..O.O....OO.O.O...............................O.O.OO....O.O..O
	.O.O..OOOOO..OO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OO..OOOOO..O.O.
	..O.OOO..OOO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OOO..OOO.O..
	....O.O..O...........................................O..O.O....
	..O.O.O..O.O.......................................O.O..O.O.O..
	..OO...O.OO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OO.O...OO..
	.........OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.........
	...............................................................
	...............................................................
	.........OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.........
	..OO...O.OO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OO.O...OO..
	..O.O.O..O.O.......................................O.O..O.O.O..
	....O.O..O...........................................O..O.O....
	..O.OOO..OOO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OOO..OOO.O..
	.O.O..OOOOO..OO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OO..OOOOO..O.O.
	O..O.O....OO.O.O...............................O.O.OO....O.O..O
	.OO..O.......O...................................O.......O..OO.
	..O.O..OOOO...OO.OOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OO...OOOO..O.O..
	..O.OO.O.O..OOO..OO.OOOOOOOOOOOOOOOOOOOOOOO.OO..OOO..O.O.OO.O..
	O.O...OO.O.O..OO.O.O.......................O.O.OO..O.O.OO...O.O
	OO.OO...OO.OO....O...........................O....OO.OO...OO.OO
	...O.OO....O.OO...OO.OOOOOOOOOOOOOOOOOOOOO.OO...OO.O....OO.O...
	...O..O.OO..OO..OOO..OO.OOOOOOOOOOOOOOO.OO..OOO..OO..OO.O..O...
	....O.O.O......O..OO.O.O...............O.O.OO..O......O.O.O....
	.....O..O...OO.OO....O...................O....OO.OO...O..O.....
	........OO..OO.O.OO...OO.OOOOOOOOOOOOO.OO...OO.O.OO..OO........
	................OO..OOO..OO.OOOOOOO.OO..OOO..OO................
	...................O..OO.O.O.......O.O.OO..O...................
	................OO.OO....O...........O....OO.OO................
	................OO.O.OO...OO.OOOOO.OO...OO.O.OO................
	....................OO..OOO..OO.OO..OOO..OO....................
	.......................O..OO.O...O.OO..O.......................
	....................OO.O.....O.O.O.....O.OO....................
	.....................O..OOO...O.O...OOO..O.....................
	.....................O...O..O.O.O.O..O...O.....................
	..................OO.O.O...OO.O.O.OO...O.O.OO..................
	..................O.OO.OO......O......OO.OO.O..................

:very long = long long

:very long house The following induction coil.

	.OOOOO.
	O..O..O
	OO...OO

:volatility The volatility of an oscillator is the size (in cells) of its rotor divided by the sum of the sizes of its rotor and its stator. In other words, it is the proportion of cells involved in the oscillator which actually oscillate. For many periods there are known oscillators with volatility 1, see for example Achim's p16, figure-8, Kok's galaxy, mazing, pentadecathlon, phoenix, relay, smiley and tumbler. The smallest period for which the existence of such statorless oscillators is undecided is 3, although Dean Hickerson showed in 1994 that there are p3 oscillators with volatility arbitrarily close to 1 (as is the case for all but finitely many periods, because of the possibility of feeding the gliders from a true period n gun into an eater).

The term "volatility" is due to Robert Wainwright. See also strict volatility.

:volcano Any of a number of p5 oscillators which produce sparks. See lightweight volcano, middleweight volcano and heavyweight volcano.

:von Neumann neighbourhood The set of all cells that are orthogonally adjacent to a cell or group of cells. The von Neumann neighbourhood of a cell can be thought of as the points at a Manhattan distance of 1 from that cell. Compare Moore neighbourhood.

Cell neighbourhoods can also be defined with a higher range. The von Neumann neighbourhood of range n can be defined recursively as the von Neumann neighbourhood of the von Neumann neighbourhood of range n-1. For example, the von Neumann neighbourhood of range 2 is the set of all cells that are orthogonally adjacent to the range-1 von Neumann neighbourhood.

:V-pentomino Conway's name for the following pentomino, a loaf predecessor.

	O..
	O..
	OOO

:Wainwright's tagalong A small p4 c/4 diagonal tagalong that has 7 cells in every phase. It is shown here attached to the back of a Canada goose.

	OOO.............
	O.........OO....
	.O......OOO.O...
	...OO..OO.......
	....O...........
	........O.....O.
	....OO...O...OO.
	...O.O.OO....O.O
	...O.O..O.OO.O..
	..O....OO.....O.
	..OO............
	..OO............

:washerwoman (2c/3 p18 fuse) A fuse by Earl Abbe.

	O.......................................................
	OO....O.....O.....O.....O.....O.....O.....O.....O.....O.
	OOO..O.O...O.O...O.O...O.O...O.O...O.O...O.O...O.O...O.O
	OO....O.....O.....O.....O.....O.....O.....O.....O.....O.
	O.......................................................

:washing machine (p2) Found by Robert Wainwright before June 1972.

	.OO.OO.
	O.OO..O
	OO....O
	.O...O.
	O....OO
	O..OO.O
	.OO.OO.

:wasp (c/3 orthogonally, p3) The following spaceship which produces a domino spark at the back. It is useful for perturbing other objects. Found by David Bell, March 1998.

	..........OO.OO.......
	........OO.O.OO.OO....
	.....OOO.O..OOO..OOOO.
	.OOO....OOO.....O....O
	O.O.O.OOO.O........OO.
	O.O.O.OOOO............
	.O.O....O..O..........
	..........O...........
	..O...................
	..O...................

:waterbear ((23,5)c/79 obliquely, p158) A self-supporting oblique macro-spaceship constructed by Brett Berger on December 28, 2014. It is currently the fastest oblique spaceship in Conway's Game of Life by several orders of magnitude, and is also the smallest known oblique spaceship in terms of bounding box, superseding the Parallel HBK. Previous oblique spaceships, the Gemini and the half-baked knightships, are stationary throughout almost all of their life cycles, as they construct the necessary mechanisms to support a sudden short move. The waterbear constructs support for (23,5)c/79 reburnable fuse reactions which are in constant motion.

:wave A wick-like structure attached at both ends to moving spaceship-like patterns, in such a way that the entire pattern is mobile. If the wave gets longer over time, the supporting patterns are wavestretchers.

Also, the gliders or spaceships emitted by a rake may be referred to as a wave, again because the line as a whole appears to move in a different direction from the individual components, due to the rake's movement. Compare with stream.

In general a wave can be interpreted as moving at a variety of different velocities, depending on which specific subcomponents are chosen as the starting and ending points for calculating speed and direction. See antstretcher, wavestretcher for a practical example of identical wave ends being connected to spaceships with different velocities.

:wavefront (p4) Found by Dave Buckingham, 1976 or earlier.

	........OO...
	........O....
	.........O...
	........OO...
	.....OO...OO.
	....O..OOO..O
	....O.....OO.
	.....O...O...
	OO.O.O...O...
	O.OO.O.OO....
	....O.O......
	....O.O......
	.....O.......

:waveguide = superstring.

:wavestretcher A spaceship pattern that supports a connection to an extensible periodic wick-like structure, whose speed and/or direction of propagation are different from those of the wavestretcher spaceship.

Connecting the following to a standard diagonal antstretcher creates a new oblique wavestretcher (a type of growing spaceship) and also an alternate space nonfiller mechanism.

	.......................................................O.....
	.......................................................OO....
	.....................................................O..O....
	....................................................O........
	.................................................OO..O.......
	................................................O..O.........
	.................................................O...........
	.............................................O...OO..........
	............................................O.OO.............
	...........................................OO..O.............
	...........................................OO.OO.............
	...........................................O..O..OO..........
	..........................................OO......OO.........
	...........................................O.OO.O.OO.........
	..........................................O.OOO.O............
	..........................................O.O.O.O............
	.............................................................
	........................................O...O................
	.......................................OO....................
	.....................................OOO..O..................
	..................................OO.OO......................
	...................................O.........................
	....................................O.O......................
	...................................O.........................
	...................................O..O......................
	..................................O..........................
	.....................................O.......................
	..................................OOOO.......................
	................................O.OO.O.......................
	.....................................O.......................
	................................O............................
	.................................O..O........................
	...................................O.........................
	.........................O....OOO....................OOO.....
	OO......................O.OOO....O......................O...O
	..OO.OO.................O..O....O....................O...O...
	..OO...OO.OO...............O..O................OO.O...O.OOOO.
	OO.....OO...OO.OO.........OO.OOO...OO..OO.OOO.O....O.....O..O
	.....OO.....OO...OO.OO......O.OO..O.O..OOO.OO.O.O...O......O.
	..........OO.....OO...OO.O...O....O.O.O..OO..O..O...OOOO.....
	...............OO.....OO..O.O.OO..O..O.......................
	....................OO...........O....O..........OO...OO.....
	.......................................O..........O..........
	....................................O........................
	....................................OO.......................
A required supporting c/5 spark is shown at the right edge. It can be supplied by a spider or another c/5 orthogonal spaceship with a similar edge spark. Alternatively, the c/5 component could theoretically be replaced by a supporting spaceship traveling diagonally at c/6, to support the same oblique trail of ants. As of August 2017 no workable c/6 component has been found.

:wedge A 26-cell quadratic growth pattern found by Nick Gotts in March 2006, based on Gotts dots. In terms of its initial population, this is the smallest known pattern with superlinear growth.

:wedge grow = wedge.

:weekender (2c/7 orthogonally, p7) Found by David Eppstein in January 2000. In April 2000 Stephen Silver found a tagalong for a pair of weekenders. At present, n weekenders pulling n-1 tagalongs constitute the only known spaceships of this speed or period, except for variants of the weekender distaff that suppress its output gliders.

	.O............O.
	.O............O.
	O.O..........O.O
	.O............O.
	.O............O.
	..O...OOOO...O..
	......OOOO......
	..OOOO....OOOO..
	................
	....O......O....
	.....OO..OO.....

:weekender distaff (2c/7, p16982) The first orthogonal 2c/7 rake, constructed by Ivan Fomichev on May 22nd, 2014. It uses the weak sparks from weekenders to perturb an LWSS into an active reaction in a variable-period loop, which produces a series of slow salvo gliders that finally rebuilds the LWSS.

:weld To join two or more still lifes or oscillators together. This is often done in order to fit the objects into a smaller space than would otherwise be possible. The simplest useful example is probably the integral sign, which can be considered as a pair of welded eater1s.

:Wheels, Life, and other Mathematical Amusements One of Martin Gardner's books (1983) that collects together material from his column in Scientific American. The last three chapters of this book contain all the Life stuff.

:why not (p2) Found by Dave Buckingham, July 1977.

	...O...
	...O.O.
	.O.....
	O.OOOOO
	.O.....
	...O.O.
	...O...

:wick A stable or oscillating linearly repeating pattern that can be made to burn at one end. See fuse.

:wickstretcher A spaceship-like object which stretches a wick that is fixed at the other end. The wick here is assumed to be in some sense connected, otherwise most puffers would qualify as wickstretchers. The first example of a wickstretcher was found in October 1992 (front end by Hartmut Holzwart and back end by Dean Hickerson) and stretches ants at a speed of c/4. This is shown below with an improved back end found by Hickerson the following month.

	.................OO..............................
	.............OO....O.............................
	............OOO.O................................
	O.OO..OO...O...OOOO.O.O....OO.......OO...........
	O....OO..O........O.OOO....O....OO.O..O.OO.O.....
	O.OO....OO.OO....O...........O...O.O.OO.O.OO.....
	......O.......O.............OO.....O..O.O...OO...
	.....O.........O.O....OOO...O....O..O.O.OOO...O..
	.....O.........O.O....OOO.OO.O..OO.O.O...O..OO.O.
	......O.......O.............OO.O...OO....OO....O.
	O.OO....OO.OO....O..........O........OO.O.O.OO.OO
	O....OO..O........O.OOO........O...O...OO.O..O.O.
	O.OO..OO...O...OOOO.O.O.......O.O...OO....O..O.O.
	............OOO.O..............O.....O.OOO....O..
	.............OO....O.................O.O.........
	.................OO...................O..........

Diagonally moving c/4 and c/12 wickstretchers have also been built: see tubstretcher and linestretcher. In July 2000 Jason Summers constructed a c/2 wickstretcher, stretching a p50 traffic jam wick, based on an earlier (October 1994) pattern by Hickerson.

:wicktrailer Any extensible tagalong, that is, one which can be attached to the back of itself, as well as to the back of a spaceship. The number of generations which it takes for the tagalong to occur again in the same place is often called the period of the wicktrailer - this has little relation to the period of the tagalong units themselves.

:windmill (p4) Found by Dean Hickerson, November 1989.

	...........O......
	.........OO.O.....
	.......OO.........
	..........OO......
	.......OOO........
	..................
	OOO...............
	...OO..OOO.OO.....
	..........OOOOOOO.
	.OOOOOOO..........
	.....OO.OOO..OO...
	...............OOO
	..................
	........OOO.......
	......OO..........
	.........OO.......
	.....O.OO.........
	......O...........

:wing The following induction coil. This is generation 2 of block and glider.

 .OO.
	O..O
	.O.O
	..OO

:WinLifeSearch Jason Summers' GUI version of lifesrc for MS Windows. It is available from http://entropymine.com/jason/life/software/.

:Winning Ways A two-volume book (1982) by Elwyn Berlekamp, John Conway and Richard Guy on mathematical games. The last chapter of the second volume concerns Life, and outlines a proof of the existence of a universal constructor.

:wire A repeating stable structure, usually fairly dense, that a signal can travel along without making any permanent change. Known wires are the diagonal 2c/3 wire, and lightspeed telegraph wire made from an orthogonal chain of beehives.

:with the grain A term used for negative spaceships traveling in zebra stripes agar, parallel to the stripes, and also for with-the-grain grey ships.

Below are three small examples of "negative spaceships" found by Gabriel Nivasch in July 1999, traveling with the grain through a stabilized finite segment of zebra stripes agar:

 .O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O.
 .OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	......................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O....................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	................................................O.....
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OOOO....OOO.
	O.........................................OO.....O...O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.....OOOOOOOOO.
	.............................................O........
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.........OO..OOO.
	O.....................................O.O.....OO.O...O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO...O.....OOO.OOO.
	.............................................O........
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.....OOOOOOOOO.
	O.........................................OO.....O...O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.OOOO....OOO.
	................................................O.....
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O....................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	......................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOO..OOO..OOO..OOO..OOOOOOOOOO.
	O..........................OO...OO...OO...OO..O......O
	.OOOOOOOOOOOOOOOOOOOOOOO...O....O....O....O.....OOOOO.
	...........................OO...OO...OO...OO...O......
	.OOOOOOOOOOOOOOOOOOOOOOOOO..OOO..OOO..OOO..OOOOOOOOOO.
	O....................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	......................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O....................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	......................................................
	.OOOOOOOOOOOOOOOOOOOOOOO..OOO..OOO..OOO..OOO..OOOOOOO.
	O........................OO...OO...OO...OO...OO......O
	.OOOOOOOOOOOOOOOOOOOOOOO...OO...OO...OO...OO...OOOOOO.
	................................................O.....
	.OOOOOOOOOOOOOOOOOOOOO...........................OOOO.
	O................................................O...O
	.OOOOOOOOOOOOOOOOOOOOO...........................OOOO.
	................................................O.....
	.OOOOOOOOOOOOOOOOOOOOOOO...OO...OO...OO...OO...OOOOOO.
	O........................OO...OO...OO...OO...OO......O
	.OOOOOOOOOOOOOOOOOOOOOOO..OOO..OOO..OOO..OOO..OOOOOOO.
	......................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	O....................................................O
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	......................................................
	.OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO.
	.O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O..O.
It has been proven that signals traveling non-destructively with the grain through zebra stripes cannot travel at less than the speed of light.

:with-the-grain grey ship A grey ship in which the region of density 1/2 consists of lines of ON cells lying parallel to the direction in which the spaceship moves. See also against-the-grain grey ship.

:WLS = WinLifeSearch

:worker bee (p9) Found by Dave Buckingham in 1972. Unlike the similar snacker this produces no sparks, and so is not very important. Like the snacker, the worker bee is extensible - it is, in fact, a finite version of the infinite oscillator which consists of six ON cells and two OFF cells alternating along a line. Note that Dean Hickerson's new snacker ends also work here.

	OO............OO
	.O............O.
	.O.O........O.O.
	..OO........OO..
	................
	.....OOOOOO.....
	................
	..OO........OO..
	.O.O........O.O.
	.O............O.
	OO............OO

:W-pentomino Conway's name for the following pentomino, a common loaf predecessor.

	O..
	OO.
	.OO

:*WSS Any of the standard orthogonal spaceships -- LWSS, MWSS, or HWSS.

:x66 (c/2 orthogonally, p4) Found by Hartmut Holzwart, July 1992. Half of this can be escorted by a HWSS. The name refers to the fact that every cell (live or dead) has at most 6 live neighbours (in contrast to spaceships based on LWSS, MWSS or HWSS). In fact this spaceship was found by a search with this restriction.

	..O......
	OO.......
	O..OOO..O
	O....OOO.
	.OOO..OO.
	.........
	.OOO..OO.
	O....OOO.
	O..OOO..O
	OO.......
	..O......

:Xlife A popular freeware Life program that runs under the X Window System. The main Life code was written by Jon Bennett, and the X code by Chuck Silvers.

:X-pentomino Conway's name for the following pentomino, a traffic light predecessor.

	.O.
	OOO
	.O.

:Y-pentomino Conway's name for the following pentomino, which rapidly dies.

	..O.
	OOOO

:zebra stripes (p1) A stable agar consisting of alternating bands of live and dead cells. Known spacefillers and many gray ships create patches of this agar. It is also the medium through which with the grain and against the grain negative spaceships travel. Many simple stabilizations of the boundaries of finite regions of this agar are known. Examples are shown below.

	..OO.......................
	..O........................
	....O..O..O..O..O..O..O....
	...OOOOOOOOOOOOOOOOOOOO....
	..O........................
	...OOOOOOOOOOOOOOOOOO......
	.....................O.....
	.OOOOOOOOOOOOOOOOOOOO......
	O..........................
	.OOOOOOOOOOOOOOOOOOOOOO....
	.......................O.OO
	.OOOOOOOOOOOOOOOOOOOO..O.OO
	O....................O.O...
	.OOOOOOOOOOOOOOOOOOOO..O...
	.......................OO..
	...OOOOOOOOOOOOOOOOOO......
	..O..................O.....
	...OOOOOOOOOOOOOOOOOO......
	...........................
	.....OO..OO.O.OOOO.OO......
	.....OO..O.OO.O..O.OO......

:Z-hexomino The following hexomino. The Z-hexomino features in the pentoad, and also in Achim's p144.

	OO.
	.O.
	.O.
	.OO

:zone of influence The set of cells on which a chosen cell or pattern can potentially exert an influence in a given number of generations N. If N is not specified it is generally taken to be one, in which case the zone of influence simply coincides with the Moore neighbourhood of the cell or pattern.

The set for N generations consists of all the cells to which at least N paths of length N can be traced from the cell(s) in question. Contrast this with the range-N Moore neighbourhood, which consists of all cells to which at least one path of length n can be traced.

:Z-pentomino Conway's name for the following pentomino, which rapidly dies.

	OO.
	.O.
	.OO

:zweiback (p30) An oscillator in which two HW volcanoes hassle a loaf. This was found by Mark Niemiec in February 1995. A smaller version using using Scot Ellison's reduced HW volcano is shown below.

	..........O..............................
	........OOOOO.................O..........
	.......O.....O..............OOOOO........
	.......O..OO.O.............O.....O.......
	...O.OOO.O.O.OO............O.OO..O.......
	...OO....O................OO.O.O.OOO.O...
	......OO.OO....................O....OO...
	.OOOOO.O.O..O.................OO.OO......
	O......O...O.O..............O..O.O.OOOOO.
	OO..OOOOO.OO.O.............O.O...O......O
	............OO.............O.OO.OOOOO..OO
	.....OO....OOO.............OO............
	.....OO....OOO.....OO......OOO....OO.....
	............OO....O..O.....OOO....OO.....
	OO..OOOOO.OO.O.....O.O.....OO............
	O......O...O.O......O......O.OO.OOOOO..OO
	.OOOOO.O.O..O..............O.O...O......O
	......OO.OO.................O..O.O.OOOOO.
	...OO....O....................OO.OO......
	...O.OOO.O.O.OO................O....OO...
	.......O..OO.O............OO.O.O.OOO.O...
	.......O.....O.............O.OO..O.......
	........OOOOO..............O.....O.......
	..........O.................OOOOO........
	..............................O..........

BIBLIOGRAPHY

David I. Bell, Spaceships in Conway's Life. Series of articles posted on comp.theory.cell-automata, Aug-Oct 1992. Now available from his website.

David I. Bell, Speed c/3 Technology in Conway's Life, 17 December 1999. Available from his website.

Elwyn R. Berlekamp, John H. Conway and Richard K. Guy, Winning Ways for your Mathematical Plays, II: Games in Particular. Academic Press, 1982.

David J Buckingham, Some Facts of Life. BYTE, December 1978.

Dave Buckingham, My Experience with B-heptominos in Oscillators. 12 October 1996. Available from Paul Callahan's website.

David J. Buckingham and Paul B. Callahan, Tight Bounds on Periodic Cell Configurations in Life. Experimental Mathematics 7:3 (1998) 221-241. Available at http://tinyurl.com/BuckinghamCallahanTightBounds.

Noam D. Elkies, The still-Life density problem and its generalizations, pp228-253 of "Voronoi's Impact on Modern Science, Book I", P. Engel, H. Syta (eds), Institute of Mathematics, Kyiv, 1998 = Vol.21 of Proc. Inst. Math. Nat. Acad. Sci. Ukraine, math.CO/9905194.

Martin Gardner, Wheels, Life, and other Mathematical Amusements. W. H. Freeman and Company, 1983.

R. Wm. Gosper, Exploiting Regularities in Large Cellular Spaces. Physica 10D (1984) 75-80.

N. M. Gotts and P. B. Callahan, Emergent structures in sparse fields of Conway's 'Game of Life', in Artificial Life VI: Proceedings of the Sixth International Conference on Artificial Life, MIT Press, 1998.

Mark D Niemiec, Life Algorithms. BYTE, January 1979.

William Poundstone, The Recursive Universe. William Morrow and Company Inc., 1985.