OCA:Just Friends
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| Just Friends | |
| View static image | |
| Rulestring | 12/2-a B2-a/S12 |
|---|---|
| Character | Semi-stable |
Just Friends is a rule created by David Bell and first described in June 2000, making it one of the first isotropic non-totalistic Life-like cellular automata considered.[note 1] It normally stabilizes into a maze-like structure consisting of lines and oscillators with escaping 3-cell spaceships.
Rule definition
The original description goes as follows:
| “ | My idea was to investigate Life rules which had birth on only two
neighbors. Using totalistic rules, this is a lose (in my opinion) since objects explode when they get two cells adjacent vertically or horizontally. But if we abandon totalistic rules, then we can fix this problem. I was looking for the combination of nicest behavior and simplest rule I could find. The most interesting rule I found was this one: A cell stays alive only if it has 1 or 2 live neighbors (in any position). A cell is born only if it has exactly two live neighbors which are not adjacent vertically or horizontally. So in the following figure, the central cell is born if there are live cells at any two cells marked ac, ad, ae, af, ag, bd, be, bf, bg, bh, ce, cf, cg, ch, df, dg, dh, eg, eh, or fh. abc hid gfe |
” |
| — David Bell, Mon, 19 Jun 2000 | ||
In Hensel notation, the rule is written as B2-a/S12, where "B2-a" transition indicates that birth does not happen on a domino surface. This prevents the formation of a replicator. A related rulespace named "SansDomino" was briefly considered in 2012, in which Just Friends would be expressed as sansdomino_s12.
Notable Patterns
Just Friends contains an infinite number of still lifes, some puffers and rakes[2], many spaceships and oscillators and some guns:
p236 glider gun by Kellie Evans, July 2000 (click above to open LifeViewer) |
Still Lifes
Just Friends has an infinite number of still lifes because any straight and crooked (though not curved) line is a still life. All still lifes are lines, or stabilizations of lines.
Notes
- ↑ A candidate for the first ever isotropic non-totalistic rule is B36n/S23, or "Ship", first described by Paul Callahan in March 1994. The name was presumably chosen due to the 6n configuration resembling a ship, and the rule itself is notable for being the closest isotropic rule to Life to feature HighLife's Replicator.[1] However, many decades earlier Roger Edwin Banks described and examined at least two isotropic non-totalistic Life-like cellular automata in his PhD thesis, namely Banks-I and Banks-III
References
- ↑ wwei23 (October 1, 2020). Re: Thread for basic non-CGOL questions (discussion thread) at the ConwayLife.com forums
- ↑ FWKnightship (August 8, 2019). Re: Just Friends (B2-a/S12) (discussion thread) at the ConwayLife.com forums
External links
Just Friends at Adam P. Goucher's Catagolue MCell built-in General binary rules: JustFriends at Mirek Wójtowicz's Cellebration page
- Just Friends (B2-a/S12) (discussion thread) at the ConwayLife.com forums
- SansDomino rulespace (discussion thread) at the ConwayLife.com forums