Resolving Jigo by Ko Threats

    Keywords: Rules

Under rule sets that allow jigo (because they have an integer komi), it can still be desirable to declare a winner in certain situations, such as knock-out tournaments or tie-breaker play-offs.

Rather than changing the komi to a fractional value, such situations could be resolved by ko threats. For this purpose, add the following rule:

In case of jigo, the last player to pass loses the game.

By introducing this rule, we introduce pass fights into the game, but only when the result is jigo.


Suppose the game has come to an end. All dame have been filled. The result, if both players now pass, will be jigo. Suppose it is Black's turn. The game will now proceed:

  • Black pass (If White now passes, she loses the game, so)
  • White ko-threat
  • Black response
  • White pass (If Black now passes, he loses the game, so)
  • Black ko-threat
  • White response
  • Black pass
  • etc.

The first player to run out of ko threats will lose the game. The player with more ko threats wins.


Theoretically, the perfect komi is an integer, and any fractional value is not 100% fair. If the perfect komi is 7, then setting the komi to either 6.5 or 7.5 will give a (very) slight advantage to one player. With this rule, the advantage is up to the players, who must maximize their own (and minimize the opponent's) ko threats. So the game becomes a little sharper, as a player must not only judge the value of moves, but must also compare otherwise equivalent moves for their ko threat potential.


Pass fights are generally considered undesirable. Although theoretically this rule only introduces them in case of jigo, in practice many players may start the pass fight in any close game, just in case they miscounted.

Reverse Reverse Button Go

The rule could be rephrased as:

In case of jigo, the last player to pass loses 1/2 a point.

in which case it might be dubbed "reverse reverse button go" :-)

willemien like the idea but in theory (i think a game should end with 3 passes) and then the rule doesn't work see how many passes to end the game

Also, some rule sets impose who passes last (eg White in AGA rules).

Resolving Jigo by Ko Threats last edited by axd on January 24, 2011 - 13:06
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