Superko

Superko is a repetition rule that prohibits a move if it would produce a board position that has already occurred earlier in the game. It prevents indefinite cyclic play, ensuring that positions based on repetition cannot continue forever. The rule is also described as positional superko or situational superko.

The exact test depends on the ruleset. Under positional superko, the board position alone is compared with earlier positions; under situational superko, the board position and the player to move are considered together. Unlike the basic ko rule, which normally bans an immediate recapture recreating the same local position, superko may forbid recreating any earlier position in the game. Rulesets differ in how they treat passes, captures, and the side to move, so positional and situational superko are not identical.