Beginner Exercise 258 / Attempts

If White ignores the corner group (1)  

In this game tree, White needs both a and b to live.

zinger: White is not dead. It is a ko. After , white plays b, and if he also gets to play a, his group is alive.

Warfreak2: Thanks, I missed that; I was thinking was still there... oops.

If White ignores the corner group (2)  

White dead again.

zinger: Same as above: white plays a, and it is ko.

White's best move  

Here, forms a bent four, which is usually a living shape. White is split into two chains, but each have three liberties. Any Black stone inside the bent four would have only two liberties, so it can be captured before Black can capture either White chain. Of course, White at either a would form two eyes, so White is alive.

QED.

At least, I think so. Anyone want to make sure I'm not missing something?

zinger: I believe black does have a way to kill white unconditionally, which is not yet shown on this page.

If White ignores the corner group (5)  

Also, am I correct in thinking that also kills White?

zinger: No. White answers at a. Now what does black do?

Warfreak2: Die, apparently. :/

clean kill  

AJP: Coming in from the outside against a J group type connection like this is a surprisingly severe attack.

Counter-example  

Warfreak2: If in your first diagram is Black's best move, then this is indeed a counter-example to Your Opponents Good Move Is Your Good Move: after is atari so White must play , then kills.

Cryptoz?: is self-atari. Black can kill at a.

Shaydwyrm: Black need not play at all after . If white plays an additional move, either a or will kill.