Life Lexicon (E)
Author: Stephen A. Silver
Description: Part of Stephen Silver's Life Lexicon.

Introduction | Bibliography

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: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 acts like an eater in two directions. 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 along four different paths.

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

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.

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

: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 + = French kiss

: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.

:egg = non-spark

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

    .OOO
    OO..
    .OO.

: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.

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

: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.

: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.......

: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.

: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.....

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