Crab
Crab  
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Pattern type  Tagalong Spaceship  

Number of cells  25  
Bounding box  13×12  
Direction  Diagonal  
Period  4  
Mod  2  
Speed  c/4  
Speed (unsimplified)  c/4  
Heat  22.0  
Discovered by  Jason Summers  
Year of discovery  2000  
 
 
 

Crab (or quarter^{[1]}) is a c/4 diagonal spaceship that was found by Jason Summers in September 2000. It is the smallest known diagonal spaceship other than the glider and it consists of two gliders pulling a tagalong.
It was noticed by Nicolay Beluchenko in August 2005 that it can be converted into a small tubstretcher, as shown below.^{[2]} This tubstretcher is the basis for the one per generation pattern.
Due to the diagonal glide symmetry and by simple inspection, the spaceship can easily be made to stretch two tub wicks simultaneously, via a domino spark repeatedly adding units to a tub or long^N barge. Additional nonstretching variants are possible by adding tubeating c/4 spaceships at the back of the chain(s), at any distance. Such a double wickstretcher was used as the basis for the Speed Demonoid.
Martin Grant found a synthesis for crab with the help of Tanner Jacobi and Brett Berger on December 26, 2014.^{[3]} The cost has since been reduced several times, most recently to 14 gliders by Tanner Jacobi on August 16, 2020.^{[4]}
Image gallery
See also
References
 ↑ "quarter". The Life Lexicon. Stephen Silver.
 ↑ H. Koenig (August 5, 2005). "New c/4 Diagonal Tubstretcher". Game of Life News. Retrieved on May 9, 2009.
 ↑ Martin Grant (December 26, 2014). "Re: How about a crab synthesis?". Retrieved on December 26, 2014.
 ↑ Tanner Jacobi (August 16, 2020). "Re: One Glider Seeds". Retrieved on August 16, 2020.
External links
 Quarter at the Life Lexicon
 25P4H1V1.1 at Heinrich Koenig's Game of Life Object Catalogs
 Crab at Adam P. Goucher's Catagolue
 Patterns
 Patterns with 25 cells
 Patterns found by Jason Summers
 Patterns found in 2000
 Patterns that can be constructed with 14 gliders
 Spaceships
 Tagalongs
 Periodic objects with minimum population 25
 Spaceships with period 4
 Diagonal spaceships
 Spaceships with speed c/4
 Spaceships with unsimplified speed c/4
 Spaceships with heat 22
 Spaceships with mod 2
 Glide symmetric spaceships