Under the Stones Problem 4 / Solution


B1 is the only move. W2 is the crucial defense in this problem. The result is a ko.

Continuation 1  

Suppose W6 is a ko threat that black answers with B7. Then after W8 retakes the ko, black cannot kill by playing under the stones with B9.

Continuation 2  

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

White's resistance is not enough  

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


B1 here fails, as white lives after W2 and W4.



Ko threat  

How about this ko threat at W6? ~ Gregory

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.

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.)

Under the Stones Problem 4 / Solution last edited by on April 18, 2023 - 14:34
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