Beginner Exercise 114 / Solution

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Two stage ko

Confused: After 3, Black needs to win the two stage ko (circled moves) to survive, while White has a local ko threat at a or b. All in all White has a good chance to profit from the situation.[1][2]

Local threat?

Charles Matthews In most cases Black will not treat White 1 here as a real ko threat, however. Black can live with 2 and 4, which allows White a sente profit but not a very big one. This should normally be better for Black than having to ignore some other threat.

Bill: Yes, W 1 is a last-ditch effort. If W plays it, she should play W 3 at 4. Then B 4 at 3, and White takes the ko, which is now a one-step (direct) ko.

[1] Bill: This talk about White's making a profit reveals a way of thinking that needs revision. Sure, White has a local advantage. And Black has made an inefficient shape. So we may expect that White has already made a profit, here. We would have to see whether Black gained anything in return to be sure. But, in any event, in future play either player may make a local profit.

[2] Bill: B 2 and W 3, making and taking the ko, are not worth as much as W 1, preventing Black's uncontested life.

Beginner Exercise 114 / Solution last edited by ryouga on January 22, 2004 - 13:02