XuanxuanQijingProblem98/Solution

[Diagram]

B4=W1.

[Diagram]

This is the best result for black: one-step ko for white and four-step ko for black.

[Diagram]

If B10 tries to make life for the black group, W11 takes away both black eyes.

[Diagram]

Another variation after W5. With W9 white avoids the ko and wins the capturing race with 5 liberties vs. 3.


This last variation shouldn't exist. First, instead of W9 at 1-1, to the left of W5 instead kills black simply while leaving no black ko threats. However, white need not play W9 locally at all; even if black got to play to the left of W5, white would take a liberty in the corner, and black would have no other move but throw a stone in at 1-1, which would create a three-move approach ko, practically meaning death for black.


I agreed, W9 played at the left of W5 is better than at 1-1. I have made the change. However, when providing a solution to a life-and-death problem, a result that avoids ko, no matter how many steps, is always preferable over ko. So I think a move does need to be played locally by white.


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