[Welcome to Sensei's Library!]

StartingPoints
ReferenceSection
About


Paths
KoFighting

Referenced by
GoTerms
Seki
TeachingGame53
Ko
ANoviceTriesToWri...
LargeAvalancheTur...
MultipleKo
OtakeHideoVsChoCh...
OneThousandAndOne...
RepeatingPositions

 

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 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.



Path: KoFighting   · Prev: FindingAKo   · Next: TwoStepKo
This is a copy of the living page "Double Ko" at Sensei's Library.
(C) the Authors, published under the OpenContent License V1.0.