Spight Rules II
Bill: The Superko Rule handles repetition during play without passes. The following end of game ko rule prevents endless play when one player passes in a position but the other one does not. Play now ends with consecutive passes. (For humans an Ing style scheme is perhaps best, ending the game with the fourth pass in a particular position. The four passes do not have to be consecutive.)
- End of Game Ko Rule: If a player passes in a particular position of the whole board and the opponent does not immediately pass, the opponent may not make a board play that repeats that position.
Since the end of game ko rule prohibits odd cycles when they are problematical, the superko rule does not have to do so. It can be a situational superko rule.
- Superko Rule: If a player makes a board play in a particular position of the whole board, the opponent may not make a board play that repeats that position, unless a pass has intervened.
Example: 2x2 board
With area scoring, Black may get greedy and try to win by one point. (This is possible under some rules, I believe.)
If Black does not pass after , he cannot repeat . But if he passes, he will lose the game by one point.
The end of game ko rule bans Black from playing in the top right corner. But now if Black continues after , he will be banned from playing at in this position, as well. Still, if he passes he loses by one point.
The end of game ko rule bans White from playing in the bottom left corner. But now if White continues after , he will be banned from playing at in this position, as well.
The end of game ko rule bans Black from making a board play, so the game ends here with a White win.
The upshot is that greed will not pay, and the game should end in a seki.
mgoetze: Sorry Bill, but I think you've got this one wrong. :) Correct komi for 2x2 is 1, so it's actually White who's being greedy by playing instead of passing. The way to punish this is by capturing instead of passing at , resulting in a win by 3 points for Black.
Then Black can play . passes and Black can accept seki. If Black does not pass, this position is banned for him, as well.
Bill: MGoetze, do you still see a Black win?
mgoetze: Hm, actually white can still get a jigo, I think:
Bill: can pass.
White has no play since he can only recreate the position after . It might not be jigo if, after W passes, B plays on, but I don't feel like analyzing it now, especially since your additional ko rule makes it more complex. :)
Bill: It's less complex when White plays a strategy of passing unless Black has more stones on the board. Then I think it's pretty clear that White can get at least jigo.