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: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.

:p144 gun A glider gun with true period 144. The first one was found by Bill Gosper in July 1994. For a full description and pattern see factory.

:p14 gun A glider gun which emits a period 14 glider stream. This is the smallest possible period for any stream, so such a gun is of great interest. There is no known true-period p14 glider gun, and finding a small direct example is well beyond current search algorithms' abilities. However, pseudo-period p14 guns have been created by injecting gliders into a higher period glider stream. The first pseudo p14 gun was built by Dieter Leithner in 1995. Smaller pseudo p14 guns have since been constructed, but they are still much too large to show here. The essential mechanism used by them is demonstrated in GIG.

: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.

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: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.

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:p184 gun A true period 184 double-barrelled glider gun found by Dave Buckingham in July 1996. The engine in this gun is a Herschel descendant. Unlike previous glider guns, the reaction flips on a diagonal so that both gliders travel in the same direction.

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: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.

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:p22 gun A true period 22 glider gun constructed by David Eppstein in August 2000, using two interacting copies of a p22 oscillator found earlier the same day by Jason Summers.

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:p246 gun A true glider gun with period 246, discovered by Dave Buckingham in June 1996. The 180-degree mod-123 symmetry of its bookend-based engine makes it trivial to modify it into a double-barrelled gun. Its single-barreled form is shown below.

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:p24 gun A glider gun with true period 24. The first one was found by Noam Elkies in June 1997. It uses three p4 oscillators to hassle a pair of traffic lights. One of the oscillators was very large and custom-made. Shown below is a much smaller version built by Jason Summers and Karel Suhajda in December 2002, using the same mechanism but with a smaller oscillator:

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:p256 gun A true period 256 four-barrelled glider gun found by Dave Buckingham in September 1995. It uses four R64 conduits to make the second smallest known Herschel loop (after the Simkin glider gun). The p256 gun was an early "teaser" from Dave Buckingham before he released his full Herschel technology.

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Either eaters or snakes can be added as shown above, to suppress three of the glider streams so that only one stream escapes. This gun's p256 glider stream is well-suited for repeated reactions with receding Corderships, or for "Hashlife-friendly" signal circuitry.

:p29 pentadecathlon hassler A hassler where two copies of a period 29 oscillator (which is itself a pre-pulsar hassler) change the period of a pentadecathlon.

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:p30 gun A glider gun with true period 30. The first one, found by Bill Gosper in November 1970 (see Gosper glider gun), was also the first gun found of any period. All known p30 glider guns are made from two or more interacting queen bee shuttles. Paul Callahan found 30 different ways that three queen bee shuttles can react to form a period 30 glider gun. One of the most interesting of these is shown below in which the gliders emerge in an unexpected direction.

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:p30 reflector = buckaroo

:p30 shuttle = queen bee shuttle

:p36 gun A glider gun with true period 36. The first one was found by Jason Summers in 2004. Shown below is a smaller version using improvements by Adam P. Goucher and Scot Ellison:

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:p44 gun A glider gun with a true period of 44. The first one was found by Dave Buckingham in April 1992. It uses two interacting copies of an oscillator which he also found. In 1996 he found a gun which only used one copy of the oscillator. Paul Callahan improved it in 1997, resulting in the gun shown below:

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:p44 MWSS gun A gun discovered by Dieter Leithner in April 1997, in a somewhat larger form. This was the smallest known gliderless gun and smallest known MWSS gun until the construction in 2017 of the gun shown under gliderless, based on Tanner's p46.

The p44 MWSS gun is based on a 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. 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.

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:p45 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:

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:p46 gun A glider gun which has true-period 46. The first one found was the new gun by Bill Gosper in 1971. Prior to the discovery of Tanner's p46 in October 2017, all known p46 guns were made from two or more twin bees shuttles that interact (e.g., see twin bees shuttle pair). See edge shooter and double-barrelled for two more of these.

On 21 October 2017 Heinrich Koenig found a glider gun using two copies of Tanner's p46 placed at right angles to each other. This is the first p46 gun found which makes no use of the twin bees shuttle.

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See gliderless for a MWSS gun also made using two copies of Tanner's p46.

:p46 shuttle = twin bees shuttle

:p48 gun A true period compound glider gun based on the p24 gun, using a Rich's p16 oscillator as a filter to remove half of the gliders from the stream.

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

: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............

:p60 gun A glider gun with a true period of 60. The first one was found by Bill Gosper in 1970 and is shown below.

	............................O..........
	............................O.O........
	...........OO..................OO......
	.........O...O.................OO....OO
	...OO...O.....O................OO....OO
	...OO..OO.O...O.............O.O........
	........O.....O.............O..........
	.........O...O.........................
	...........OO..........................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	.......................................
	..........O.O..........................
	.........O..O...OO.....................
	OO......OO.....OOO.OO..OO..............
	OO....OO...O...O...O...O.O.............
	........OO.....O.O........O............
	.........O..O..OO......O..O............
	..........O.O.............O............
	.......................O.O.......OO....
	.......................OO........O.O...
	...................................O...
	...................................OO..
There are several other ways to create a p60 gun from two p30 guns using period-doubling reactions similar to the one shown here.

:p690 gun A true period 690 glider gun found by Noam Elkies in July 1996. It is composed of a p30 queen bee shuttle pair and a p46 twin bees shuttle whose sparks occasionally react with each other. This is a very compact gun for such a high period and is used in many patterns requiring sparse glider streams.

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

: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 minimum 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...............

:p90 gun A glider gun with true period 90. The one below by Dean Hickerson uses the output of two p30 guns in a period-multiplying reaction:

	......................................O.........................
	......................................OOOO......................
	................................OO.....OOOO.......O.............
	...........................O...O..O....O..O......O.O............
	..........................O.O...OO.....OOOO....OO...O...........
	.........OO...............OO.O........OOOO.....OO...O.........OO
	.........O.O..............OO.OO.......O........OO...O.........OO
	....OO......O.............OO.O...................O.O............
	OO.O..O..O..O.............O.O.....................O.............
	OO..OO......O........O.....O...........O.O......................
	.........O.O.......O.O.................OO.......................
	.........OO.........OO..................O.......................
	................................................................
	................................................................
	...........................................OO...................
	...........................................OO...................
	................................................................
	................................................................
	................................................................
	................................................................
	................................................................
	................................................................
	........................................OO......................
	........................................O.......................
	.........................................OOO....................
	...........................................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) An uncommon 180-degree rotationally symmetric 14-bit still life. The Iwona methuselah contains a paperclip in its ash.

	..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 generator 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 others have none at all (see Garden of Eden). Typically parents are considered trivial if they contain groups of cells that can be removed without changing the result, such as isolated faraway cells. Finite patterns have only a finite number of non-trivial parents.

: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. Only the even/odd parity is important.

:partial result An intermediate object found by a search program which might be a substantial part of a complete spaceship or oscillator, but which isn't complete.

Running a partial result works for a few generations until the speed of light corruption from any unfinished edge destroys the whole object. But a partial result can still be used to see whether the object (if ever finished) would provide a desired spark or perturbation. If no partial results are found than it is likely that no such object exists under the constraints of the search.

Very large partial results can indicate that there is a good chance that the object being searched for might actually exist (but this is no guarantee). Rerunning the search using the partial result as a base and relaxing some constraints, widening or adjusting the search area, or splitting the object into multiple arms might result in finding a complete working object.

As an example, here is a large partial result for a period 6 knightship found by Josh Ball in April 2017. See also almost knightship for an earlier small example by Eugene Langvagen.

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

:PD = pentadecathlon

:PD hassler = p29 pentadecathlon hassler

:PD-pair reflector A pair of pentadecathlons arranged so that their V sparks turn a glider by 90 degrees. Minimum repeat time is 45 ticks.

	..............OOO......
	.......................
	.............O...O.....
	.............O...O.....
	.......................
	..............OOO......
	.......................
	.......................
	..............OOO......
	.......................
	.............O...O.....
	.............O...O.....
	....................O..
	..............OOO...O.O
	....................OO.
	.......................
	O..O.OO.O..O...........
	OOOO.OO.OOOO...........
	O..O.OO.O..O...........
This was found by Mark Niemiec on 6 January 1996, which is relatively recent considering how old pentadecathlon technology is.

: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. The pentadecathlon can be constructed using just three gliders, as shown in glider synthesis.

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

The pentadecathlon is the only known oscillator that has two phases that are different polyominoes. It produces accessible V sparks and domino sparks, which give it a great capacity for doing perturbations, especially for period 30 based technology. See relay for example.

: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 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.

:periodic For circuit mechanisms, "periodic" is the opposite of p1 or stable. Periodic circuits necessarily contain oscillators, and therefore they can generally only accept input signals that are synchronized to the combined period of those oscillators (but see universal regulator).

For signal streams, "periodic" means that signals will only be present in the stream at one out of every n ticks, where n is the period of the stream. In an intermittent periodic stream there may be gaps, so that signals do not always appear at every nth tick. However, if a signal does appear, its distance measured in ticks from previous and future signals will always be an exact multiple of n.

:period multiplier A term commonly used for a pulse divider, because dividing the number of signals in a regular stream by N necessarily multiplies the period by N. The term "period multiplier" can be somewhat misleading in this context, because most such circuits can accept input streams that are not strictly periodic.

Reactions have also been found to period double or period triple the output of some rakes to create high-period rakes in a relatively small space (i.e., an exponential increase in period for a linear increase in size).

For Herschel signals and glider guns, a number of small period doubler, tripler, and quadrupler mechanisms are known. For example, the following conduit produces one output glider after accepting four input B-heptominoes, or four Herschels if a conduit such as F117 is prepended that includes the same BFx59H converter.

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

See semi-Snark and tremi-Snark for additional examples using glider streams. No elementary stable period-multiplying conduits are known for a multiplication factor of five or higher, though it is easy to construct composite ones.

: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 forward or backward 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.
One oscillator which produces this spark is Tanner's p46. The pentadecathlon produces a slightly corrupted version of this spark.

: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....
This is extensible and is just the first of a family of phoenixes made by joining components together to form a loop. Here is another member of this family.
	.....................O.......O......
	.....................O.O.....O.O....
	.................O.O.....O.O........
	.................O.......O......OO..
	.....O.......O.O....................
	.....O.O.....O...................O..
	...O.....O.O........................
	.........O........................OO
	..OO................................
	..................................O.
	.O..................................
	................................OO..
	OO........................O.........
	........................O.O.....O...
	..O...................O.....O.O.....
	....................O.O.......O.....
	..OO......O.......O.................
	........O.O.....O.O.................
	....O.O.....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.

An easy synthesis of the phoenix is possible using four blocks as seeds. A puffer creating a growing row of phoenixes has the unusual property that the percentage of live cells that stay alive for more than one generation approaches zero. See lone dot agar for an example of an infinite phoenix.

: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 with period 30, 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.

The pattern below shows the basic mechanism of a PPS. The two isolated sparks at the left and right sides are the edge sparks from the two supporting spiders.

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

: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-pre-block A common predecessor to the pre-block (and thus the block):

	O.O
	.OO
This is easily created by a two-glider collision. Hitting the pre-pre-block with a glider can create a MWSS. Both of these reactions are shown below:
	.O..........
	..O.........
	OOO.........
	............
	............
	...OOO....OO
	.....O...OO.
	....O......O

: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. The pre-pulsar was also a vital component of the first known p26 and p47 oscillators.

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 greater than n. This period will necessarily be a multiple of n. If the base mechanism's period is instead a fraction of n, then a period multiplier must also be present which is considered to be part of the mechanism, and the gun as a whole is still a true period gun. For example, a filter may be used on a lower-period gun to produce a compound gun such as the true p48 gun.

Pseudo period n glider guns are known to exist for all periods greater than or equal to 14, with smaller periods being impossible. All known p14 guns are pseudo guns requiring several signal injections, so they are quite large. The following smaller example is a pseudo period 123 gun, interleaving the streams from two true period 246 guns:

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

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. See also barberpole.

	..........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 A stable pattern whose live cells are either immediately adjacent to each other, or are connected into a single group by adjacent dead cells where birth is suppressed by overpopulation.

The definition of strict 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, and have been enumerated up to 32 bits, as shown in the table 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
	--------------

Attribution of these counts is given in strict still life; see also https://oeis.org/A056613. The unique 32-bit triple pseudo still life is included in the last count in the table.

If a stable pattern's live cells plus its overpopulated dead cells do not form a single mutually adjacent group, the pattern is usually referred to as a constellation. It is also a still life in the general sense, but is neither "pseudo" nor "strict".

: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).

	.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..

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. Other new puffer speeds followed over the next several years.

Many spaceships that travel orthogonally at a speed less than c/2 have useful side or back sparks. These can be used to perturb standard spaceships that approach from behind. A common technique for creating puffers for a new speed uses a convoy of the new spaceships to create debris from an approaching standard spaceship such that a new standard spaceship is recreated on the same path as the original one. This forms a closed loop, resulting in a high-period puffer for the new speed.

As of this writing (November 2017) puffers have been found matching every known velocity of elementary spaceship, except for c/6 and c/7 diagonal.

: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....
See soup for a random initial pattern, generated by apgsearch and recorded in Catagolue, that produces a pufferfish.

: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 puffers, 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.)

: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


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