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Double Ko
Path: KoFighting   · Prev: FindingAKo   · Next: TwoStepKo
  Difficulty: Beginner   Keywords: Ko

[Diagram]
Diag.: Double ko

The diagram shows an occurrence of a double Ko. (From LargeAvalancheTurnInward). The black group has one liberty (the marked eye) and two kos, giving him always two liberties. If white takes away a liberty by taking the ko at 'a', black can take the ko at 'b'. It is then up to white to find a ko-threat. Black can answer the ko threat, and when white recaptures at 'b', black takes 'a'. It is again white who has to play a ko-threat, which black can answer.

It should be clear that white cannot win in this situation - he is dead through double ko.

A point worth mentioning is that a double ko can serve as an infite supply of ko-threats to the player at a disadvantage (in this case, white). This is because white 'a' does require black to answer at 'b' and vice versa. This means that white will win any ko on the board which is worth less than the double ko.

--MortenPahle

TakeNGive (11k): Wow. What happens to this kind of shape under the Ing Ko Rules?

unkx80: White is dead, and if I'm not wrong, white has only two ko-threats under the Ing Ko Rules, not infinite. See Disturbing Kos for more information.

TakeNGive: Thanks unkx. A double ko recently came up in my tournament game. Luckily for me, we were not using Ing rules; but I'm curious whether this was a disturbing or fighting ko, and whether the line of play would have been legal under Ing rules. Please have a look at my DoubleKoQuestion.



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