Gun

A gun is a stationary pattern that emits spaceships (or rakes) repeatedly forever. By far the most common type of guns are glider guns, which emit gliders (the most well-known of which is the Gosper glider gun), though guns that emit other spaceships such as the lightweight spaceship are known. There are even known guns for many of the Corderships (see V gun for an example). Such non-glider guns are usually constructed by positioning several glider guns so as to create the larger spaceship by glider synthesis.

Barrels

It is not uncommon for glider guns to have multiple barrels; that is, streams of gliders that come out along multiple different paths. For example, the B-52 bomber is said to be double-barreled because it produces two streams of gliders (one toward the northwest and another toward the southeast). Gunstar and its variants all have four barrels, and P94S contains a whopping 12 barrels. Given a gun with multiple barrels, one can eliminate barrels by simply placing an eater 1 in the path of the unwanted glider streams.

Pseudo-period guns

A pseudo-period gun (as opposed to a true-period gun) is a gun that emits a period n stream of spaceships (or rakes) via a mechanism that 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 period 14 gun was built by Dieter Leithner in 1995.

True-period guns

A true-period gun (as opposed to a pseudo-period gun) is a gun that emits a period n stream of spaceships (or rakes) via a mechanism oscillates with period equal to n. True period n guns are known to exist for all periods greater than 61, but only a few smaller periods have been achieved, namely 22, 24, 30, 44, 46, 48, 50, 54, 55, 56 and 60. Credits for these small period guns are: p30, p46 and p60 by Bill Gosper in 1970-1971, p44 by David 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 and p22 by David Eppstein in 2000.

See also

• List of guns

External links

• Gun at the Life Lexicon