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There are in particular these variants of the superko rule:
- Positional Superko: Forbids a board play to repeat a board position. See Positional Superko / Example. The Chinese rules (albeit theoretically,) and the Tromp-Taylor Rules use this version.
- Situational Superko: Forbids a board play to repeat a board position with the same player to move, regardless whether earlier it was created by a board play or pass play. The AGA rules and New Zealand rules use this version.
- Natural Situational Superko: Forbids a player's board play to repeat a board position if earlier it was created by his board play. According to Terry Benson, AGA rules were meant to use Natural Situational Superko, but everybody else interprets them with Situational Superko.
Additionally, some rules take into account whether players have passed for determining whether a move is legal.
There is an additional implementation format which forms Chinese Superko.
The most commonly used example why a superko rule is necessary is triple ko. See below for a more simple case that also illustrates the rule:
This situation is a seki in the corner. Assume Black just passed, so that this position has occurred with either side to play. If White plays at a, Black plays b. With a superko rule in place, White cannot retake at , so Black can take the corner. Of course, this comes from a White initial mistake, but see Rules Beast 1 for a case where White breaks the seki and wins the fight...
- Fixed ko rule: repeated positions may occur but you are not allowed to make the same move in them.
- Long cycle rules: Rather than forbidding the repetition a board position, this rule assigns a result to the game if a repetition occurs. The game result depends on the number of stones captured by either since the first occurrence of the position. The Computer Olympiad rules use this version.
- Short cycle rules?: The result depends on the number of moves between the repeats. If there are 3 or fewer moves between the repeats the game is a loss for the player who makes the repeat. If there are more moves between the repeats the game is a draw.
- No result: The Japanese rules and Korean rules say that if a board position is repeated, the game has no result; this usually means the game must be replayed.
- Article 7: The repetition of the same pattern shall be prohibited unless the right to an alternate move is disregarded.
In modern terms, "disregarding the right to an alternate play" means passing. When a pass lifts a ko or superko ban, this is sometimes called "pass for ko threat". There are different versions of the superko rule in which an intervening pass allows a repetition. Yasunaga's seems to say that any intervening pass lifts the restriction on repetition, but it may mean a pass by the player who makes the repetition. The interaction with passes can pose problems with ending the game, but not taking passes into account can lead to strange results. My home page, when I get it up, will have a discussion, and my solution to the problem, based on Combinatorial Game Theory. Meanwhile, for my solution, see Spight Rules.
Yasunaga proposed a three-consecutive-pass rule, which is how my solution will usually work. Ing uses a four-pass rule.