Ko rule Go (game)

players not allowed make move returns game previous position. rule, called ko rule, prevents unending repetition. shown in example pictured: black has played stone marked 1, capturing white stone @ intersection marked red circle. if white allowed play on marked intersection, move capture black stone marked 1 , recreate situation before black made move marked 1. allowing result in unending cycle of captures both players. ko rule therefore prohibits white playing @ marked intersection immediately. instead white must play elsewhere, or pass; black can end ko filling @ marked intersection, creating five-stone black chain. if white wants continue ko (that specific repeating position), white tries find play elsewhere on board black must answer; if black answers, white can retake ko. repetition of such exchanges called ko fight.

while various rule-sets agree on ko rule prohibiting returning board previous position, deal in different ways relatively uncommon situation in player might recreate past position further removed. see rules of go: repetition further information.