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Double Ko
Path: SecondCourseOnKo   · Prev: HonKo   · Next: DoubleKoQuestion
  Difficulty: Beginner   Keywords: Ko

[Diagram]
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 at 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 - she is dead in double ko.



A point worth mentioning is that a double ko can serve as an infinite 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 an infinite number. 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.


[Diagram]
Two-Side Double Ko?

This situation would be like a double ko for both sides, so both sides would have infinite ko threats. Wouldn't any additional ko that is worth less than this corner then lead to a TripleKo?

--Harleqin



Charles There are also connections that work because of double ko, as well as groups that have two eyes thanks to a pair of kos.



Path: SecondCourseOnKo   · Prev: HonKo   · Next: DoubleKoQuestion
This is a copy of the living page "Double Ko" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.