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KyuExercise7

 

Kyu Exercise 7 Solution
  Difficulty: Advanced   Keywords: Life & Death, Problem

Preamble:

[Diagram]
Time is of the essence

The marked black stones have only two turns of aji left in them - the first move is nearly certain to be ate.


[Diagram]
Variation 'a' fails

After this sequence up to W4, Black needs at least three turns to capture the eye - because strange things happen in the corner. Black must first connect before taking the corner liberty - and by then it's too late.

Dieter: When Black connects at B5, he dies in gote. White needn't play W6. Earlier, White can also answer B3 with W4 at W8, but in fact this leaves a ko threat behind, so answering at W4 is probably correct.


[Diagram]
Variation 'b' fails

Black now needs at least five turns to kill White - she could tenuki here without worry. B3 dies in gote.


[Diagram]
Variation 'c' - success

The only sequence. Black's win of this ko captures first the marked White stone, followed by the rest of the group. Notice that White captures first - but it's better than death. Question - so this is a two stage ko?

unkx80: Yes, this is a two stage ko. This is also the solution. If W2 plays at B3, Black will catch all the white stones in a snapback at a.


[Diagram]
Variation c - success, continued

Hattu (27k): I had a lot of trouble with this tsumego after counting up to the position after B1. I first discarded this variation - thinking that white stone at a next turn will win the battle without doubt. It's an important piece of knowledge to learn what is a ko threat and why they are important. B3 is one of those: it threatens to escape with the black group in danger, so White has to defend with W4, or she won't benefit too much from winning the ko. This gives Black the chance to play at the marked stone, and even further at b next turn, if White can't come up with a decent ko threat to answer with.

Of course White will count the number of good ko threats in the board and look around the left border, and decide if playing at W4 or a is better. If Black has more good threats than White, and the left edge was going to be black territory anyway, White could always just allow Black to escape down the left side with the play at a. At least White lives in the corner, and can build up good influence against the black stones which are running towards the lower right corner.


[Diagram]
Variation 'd' - failure

As in Variation a, Black needs three turns in this variation, and dies in a similar fashion.



This is a copy of the living page "Kyu Exercise 7 Solution" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.