A collection of (il)legal cyclic Go positions
 Ko  the simplest and cycletopological only 2cycle

 Infinite yose  the 4cycle with single pass

 Eternal life  the 4cycle at the edge

 TripelKo  a 6cycle to get seki

 DoppleKo seki  a 6cycle with 2 passes in a seki

 Moon shine life  a 6cycle to force life for another group

 Simplified Shimada  a 6cycle with ko and ko threat

Remark: the center ko should be of a little more value, to prevent each
player's option, in opposite to give atari with two stones, to connect solidly
and threaten to change the opponent's edge group life into ko.
 RoundRobinKo  an 8cycle in a seki

 Biliteral DoubleKo seki  an 8cycle in a seki

 Shimada's Ko  a 10cycle with twostage ko and ko threat (Shimada Takuya 1958)

 The Pendulum  a 10cycle with ko and ko threat (Matti Siivola 1983)

 MolassesKo  another 10cycle with 2 passes in a seki (T. Mark Hall 1993/94)

Remark:
together with the position consisting of two independent simple Kos
the above mentioned two 4cycle positions represent all existing
cycletopological different 4cyclic Go positions.
Diagrams were composed with xigc4.1 / xv3.10 / gifmerge1.33 / giftrans1.11.
So my thanks go to: Steve Coffin,
John Bradley,
Mark Podlipec, Rene Mueller, and
Andreas Ley
for writing PDsoftware which is sourcecode availible!
Achim Flammenkamp
enlarged: 20031028 15:25 UTC+01