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ApproachMove
Furikawari
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TwoStepKo
LargeAvalancheTur...
KoThreatPlayingOrder
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GoTerms
TwoStageKo
KanazawaSolution21
KanazawaSolution11

 

Approach Ko
Path: SecondCourseOnKo   · Prev: DanKo   · Next: TwoStepKo
    Keywords: Ko

A ko is called an approach ko for White (Black) if White (Black) cannot win the ko without making an approach move. The Japanese term for it is yoseko.

[Diagram]
Approach ko

In this diagram, Black and White are involved in a ko fight around the position of the marked black stone and a. If Black wins this ko fight, he can capture the white stones and end the ko, but before White can win the ko fight, she will first have to fill up a liberty at b. Black can then re-take the ko, which will then be fought out the normal way. Thus, White will have to win this ko twice before getting what she wants. By way of contrast, Black can capture the White stones immediately. Black need to ignore at most one ko threat to capture White, whereas White may need to ignore one ko threat to play at a capturing Black's single stone, and then ignore another ko threat to play at b.



Going on, if Black had even more liberties we could also get a two-move approach ko, a three-move approach ko, etc.

White's chances of winning the ko do of course diminish the more often she would have to win it. A two-move approach ko can be considered a reasonable fight, although worse than a direct ko of course, but a five- or six-move approach ko is rarely worth fighting.

There is a saying, "A three-move approach ko is no ko."

White will have to ignore several black ko threats, which will probably cost her more than the ko will bring her. Alternatively, Black can play several ko threats and have them ignored; and then win the ko by ignoring only one ko threat himself.

The size of the ko threats should increase after each approach move. With correct play, this balances the effect of leaving ko threats unanswered.

The count of an approach ko depends on who is its KoMaster. In this case it makes a difference of 5 3/4 points. See KoMaster for the calculation.


Authors: Morten Pahle, BillSpight
Wiki-editor: Dieter Verhofstadt



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