Under the Stones Problem 4 / Solution

[Diagram]
Ko  

This is a ko. Assuming W6 is a ko threat and black answers with B7 then black cannot kill by playing under the stones as shown in the next two diagrams.

[Diagram]
Continuation 1  
[Diagram]
Continuation 2  

And white is alive because of his second eye at a.

[Diagram]
White's resistance is not enough  

W2 is not the best move. B7 under black+circle.


[Diagram]
Ko threat  

How about this ko threat at W6? ~ Gregory

[Diagram]
Variations of reply #1  

If Black replys to ko threat at B1 then White takes ko and Black has to find the big ko threat to force White's response and then retake ko.

[Diagram]
Variations of reply #2  

If Black ignores the ko threat and takes with B1, then W2.

If B3 @ b then W4 @ c, and if B5 attacks on top at e or f, then W6 at a captures the four Black stones with the double cut; and if B5 connects on the bottom then W6 at f gets the second eye.

If B3 on top at d, e, or f, then W4 still at c, Black connects on the bottom at D-1 or F-1 to protect against the double cut, and W6 at b makes White's second eye. (In the case of B3 at e white may fill to protect W3 and threaten the cut at f making f and b miai for the second eye.)


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Under the Stones Problem 4 / Solution last edited by GregoryWonderwheel on August 11, 2008 - 09:52
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