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BeginnerExercise18

 

Beginner Exercise 18 Solution
   

[Diagram]
Diag.: Black kills white

If black plays first he can kill white by playing 1. White has to answer at 2 otherwise black's stones can escape to the marked stone and white dies.

Next black plays 3. Note that this play reduces white's eye space - it is no longer possible for her to make an eye at B1.

White has to capture at 4. If she does not, black captures W2 and his stones escape.


[Diagram]
Diag.: Position reached

In this position we see that white's eye space are 4 points in a row (the circles). The square point is not an eye room (imagine black playing at 'a').

But four in a row (BentFour) lives, I hear you say. That's true, but only if its borders are completely defined. Here, one side is still open. So ...


[Diagram]
Diag.: continued

Black plays at '1' ('There Is Death In The Hane') and reduces the potential eye-space of white to ThreeInARow. However, white would have to capture black 1 and divide the space with one move - something not possible.

White's best attempt is to play at '2'. But this fails as well. Black plays at 3 and even if white captures the two stones with 'a' black plays again at '1' and white is left with only one eye.



[Diagram]
Diag.: Failure

Black 1 here is a mistake. It robs the black stones of an essential liberty.


[Diagram]
Diag.: Black tesuji? No chance.

If black tries to falsify an eye with 5 at f, white 6 at a leaves a living BentFour. Any play inside is met easily by white 6 at f. Black can play inside a second time, but it's no use - that's only two plays, and any of the three points b, c and d let white DivideTheSpace, and there are no cutting points to exploit.

Even if white were careless and let black take all three points while playing tenuki, it would just make seki. (That only costs white 6 points actually; 4 in territory after making the eyes, plus two prisoners. But Black can later sacrifice that seki at an 8-point cost, and get two ko threats out of it. Tenuki plus two points net in exchange for two ko threats... any expert opinions on that trade-off?)



Arno, SAS, KarlKnechtel




This is a copy of the living page "Beginner Exercise 18 Solution" at Sensei's Library.
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