Editing Go (game) (section)

=== Ko rule ===
{{main|Ko fight}}
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{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|  b|  w|   |  r
|  b|  c| b1|  w|  r
|  l|  b|  w|   |  r
| dl|  d|  d|  d| dr|32}}

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An example of a situation in which the ko rule applies
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Players are not allowed to make a move that returns the game to the immediately prior position. This rule, called the [[ko rule]], prevents unending repetition (a stalemate).{{sfn|Kim|Jeong|1997|pp=48–49}} As shown in the example pictured: White had a stone where the red circle was, and Black has just captured it by playing a stone at '''1''' (so the White stone has been removed). However, it is readily apparent that now Black's stone at '''1''' is immediately threatened by the three surrounding White stones. If White were allowed to play again on the red circle, it would return the situation to the original one, but the ''ko'' rule forbids that kind of endless repetition. Thus, White is forced to move elsewhere, or pass. If White wants to recapture Black's stone at '''1''', White must attack Black somewhere else on the board so forcefully that Black moves elsewhere to counter that, giving White that chance. If White's forcing move is successful, it is termed "gaining the ''sente''"; if Black responds elsewhere on the board, then White can retake Black's stone at '''1''', and the ''ko'' continues, but this time Black must move elsewhere. A repetition of such exchanges is called a ''ko fight''.{{sfn|Kim|Jeong|1997|pp=144–147}} To stop the potential for ''ko fights'', two stones of the same color would need to be added to the group, making either a group of 5 Black or 5 White stones.

While the various rulesets agree on the ko rule prohibiting returning the board to an ''immediately'' previous position, they deal in different ways with the relatively uncommon situation in which a player might recreate a past position that is further removed. See {{section link|Rules of Go|Repetition}} for further information.