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November 2000's Go Answer of the Month

I recently played a 13*13 handicap game against a novice player. In that game the situation in Dia 1 almost occurred. The actual situation had an additional black stone at A.

Dia 1 - Black to play.

Dia 1

What should happen with Black to play in the two situations: with and without a black stone already at A?

Dia 2 - When there is a Black stone at A.

Dia 2
White 4 at 1.

In this case Black simply sets up a shortage of liberties with 1 and captures the six white stones on the left.

Dia 3 - And when A is empty.

It turns out that the situation is much more involved. If Black tries the same tactic...

Dia 3
White 4 at 1.

... White can then play a move such as 8 to make the large white group safe and get a semeai in the corner.

Dia 4 - One variant of the corner semeai.

Dia 4

9 is a vital point to prevent White getting eyes hard in the corner. However the 10, 12, 16 combination look to be a tesuji threatening an eye on the lower edge.

White could play 22' at 19 and let both groups live. Playing 22 denies Black a second eye though white has to cope with Black 23' at 19.The problem then spills out to the left, the cutting points in the black wall being significant. As the problem did not show what had already been played in this part of the board, I'm no tanalysing this further now.

I haven't yet found a sequence where Black can definitely live in the corner. Every time I find one that looks promising I come up with a White refutation. But my investigation has not been exhaustive.
Please let me know if you find one.

If White wants a simple life, he can let both groups live in the corner.

Dia 5 - All groups live.

Dia 5

White 12' at 13 gets Black 13' at 12 and the large White dango dies straightforwardly.

Dia 6 & 7 - What if Black starts in the corner?

Dia 6   Dia 7
White 21 at 17.

Black is too slow here, he is a liberty short.

Again I haven't managed a complete investigation, but each variation I've tried has had a White success!

It may, perhaps, be worth returning to this problem in a later month. What do you think?

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