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November 1998's Go Answer of the Month

Dia 1 - What are the possibilities?

Dia 1

I had White against Jackie Chai (2k) in the first round of this year's Wessex Tournament. During that game, roughly this situation occurred. I spent some time trying to see what, if anything could be done by White against the black corner, and whether Black needed a move to protect it.

What possibilities are there in the corner?

Dia 2 - Poor play.

Dia 2

This definitely shows how Black does not want to play. The Black atari of 2 forces the counter atari of 3 and after 5, Black 4 etc have one fewer liberties than White 5 etc.

Equally poor, for White, is any other 1' since then Black connects or protects the cutting point of 1 here.

Dias 3 & 4 - Not a ko!

At Marlborough, I was informed that (when there are no outside weaknesses) this becomes a ko - and it was demonstrated. My initial attempts at recreating the situation - even after adding the White triangle stone in the next few diagrams - keep resulting in White dying.

Dia 3   Dia 4

Dia 3 shows my initial thoughts, the White atari at 7 gains enough tempo to permit an atari on 6 by 9. When Black captures with 10, 11 starts a ko (at 11 & 12). Except that in this situation Black shouldn't capture with 10', but should descend at 11.
Dia 4 has this descent which repudiates white 9. It also shows one of the many White 11 follow-ups that fail.

Dias 5, 6 & 7 - Still not a ko!

Dia 5   Dia 6   Dia 7

In Dia 5, White tries descending on the outside with 9. Black matches it with the descent to the first line of 10 - and gets caught in a snapback.
So in Dia 6, by using 12 to capture the White stone, Black avoids the snapback and then 13 forms a ko.
But Black 10 in Dia 7 repudiates both of these sequences with a straight kill.

Dias 8 & 9 - Ko at last.

Dia 8   Dia 9

This White 9 does lead to one of two kos.

Dia 10 - Back to the original question.

Dia 10

If the White triangle stone which was added in the previous diagrams is removed, does it make a difference?
It makes no difference to the direct kos of Dias 8 & 9, however it does permit Black the option of letting White live in the corner and linking his four stones out by capturing the two White cutting stones. That may well be a bad idea for Black as his left side stones then get captured - it all depends on how big the top side is.

If it is Black to play in the original position, Black 1' at 8 in Dia 3 is sufficient and White 2' ought to protect his cuttings stones with the triangle move or equivalent.

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