Ing Ko Rule
Ko prevents invariations; classified as fighting or disturbing.
Invariations: Invariation is the cyclic repetition of board positions, when both sides refuse to yield. Invariations result in games with no outcome. How to prevent all invariations was the enigma which puzzled rule makers for almost five thousand years.
Ko: Ko prevents invariations. These rules classify ko as fighting or disturbing. Repeated removal of ko stones after intervening board or pass plays is a ko fight, cyclic removal of ko stones is disturbing. The hot stone rule prevents invariations by disallowing the removal of hot stones (i.e., immediate recapturing of ko stones without an intervening board or pass play) in a ko fight. The disturbing ko rule prevents invariations by forbidding the disturber from disturbing after one complete cycle (of repeated board positions). Since all the invariations are accounted for, every life and death shape can be resolved.
Ko shapes: When two opposing groups are locked together in the tigerís-mouth shape, the stones in the opposing sideís mouth can be removed repeatedly and are known as ko stones. There are large, medium and small tigerís mouth and single, double and triple ko stones.
Fighting ko: A fighting ko determines the life and death of the opposing groups involved. The ko stones in the repeated fight are called hot stones. Hot stones cannot be removed until after an intervening board or pass play.
Hot stone: Tradition rules only have single hot stone rule. The Ing rules created double and twin hot stone rules. In an eternal life position, double hot stones are formed when a stone is added to another to make double ko stones, these become double hot stones. In a triple ko fight, besides the single hot stone there is another single or double ko stone; these are also regarded as hot stones, known as twin hot stones.
Disturbing ko: A disturbing ko is the cyclic removal of ko stones initiated by the disturber by either fighting an unnecessary hot stone fight or recycling ko threats. If either side refuses to give in, cyclic removal of ko stones is resulted. Not only does this prevent the game from ending, it serves no purpose. After one complete cycle, the disturber is never allowed to continue disturbing. For any disturbing ko, every move in the second cycle or subsequent cycles causes invariation, and the disturber can be forbidden from disturbing at any time, enabling the game to end.
These rules have been criticized for a lack of clarity in distinguishing fighting kos from disturbing kos, and for other reasons. See Discussion.