lightvector wrote:
If you want to avoid this kind of pathology, but still break all cycles, guarantee that games are finite, and handle the "basic" situations the way that most players' intuitions think they should be handled (of course there are always still more complex rules beasts), you can use Bill Spight's innovation regarding ko bans and game end:
Use a superko rule as normal, except:
1. Passes lift all ko bans (superko only stops repetitions where neither player passed in between).
2. Regardless of what passes occur in between or not, the game ends when a player passes in a position that player previously passed in. (and this is the only game end condition now. So in normal games it means that the game usually ends with 3 consecutive passes, not 2).
#1 is of course targeted at breaking the kinds of positions in this thread.
Intuition for #2 is to say that even if ko bans are lifted, we can still end the game in the case of cycles involving enough passes, because passes usually indicate one or both players have nothing better to do.
In normal cases with 3 passes, the "hand talk" is like:
P1 passes: "I have nothing I want to do *except* maybe I'm just waiting to recapture a ko and have no other non-suicidal moves"
P2 passes: "I have nothing I want to do, not even with ko bans lifted"
P1 passes: "I have nothing I want to do, not even with ko bans lifted - okay the game should end since neither player has useful things to do".
In cases with unbalanced repetition where only 1 player is passing while the other player cycles, the "hand talk" is like:
P1 passes: "I have nothing I want to do *except* maybe I'm just waiting to recapture a ko and have no other non-suicidal moves"
P2 plays some moves that force P1 to respond, but they only lead back to the same position where P1 passes originally.
P1 passes: "I still have nothing I want to do, and if the best that you, P2, could do even with all ko bans lifted and a free extra turn was merely to cycle back to the same position where I can pass yet again, then obviously you're just wasting time, the game should end now."
By beginning your post by "If you want to avoid this kind of pathology..." you seem quite careful and I agree with that.
As far as I am concerned it is not really a pathology but simply a consequence of the rule which does not hurt me for two reasons:
1) It will never happen in practice on a 19x19 board and I have even great doubt it can happen in practice on a 9x9 board.
2) On a smaller board this result seems even interesting and remind me the zugswang in chess. I you like very small boards what really harms by taking care of such possibility?
IOW it is for me only a curiosity of the rule as suggested by the title I chose.
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Gérard TAILLE
