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It is frequently the case that I do a problem from a book and the answer leaves the situation before it has become clear to me!
Dia 1 is such a situation. Is Dia 1 a correct or a failure diagram (for black)? What happens next?
This diagram is from page 73 of Yang Yilun's Yutopian book "Rescue and Capture". The comment given there on Dia 1 is: Failure: Black 1 is a thank you move. After White connects at 2, Black 3, 5 and 7 are the best way to go, but Black cannot live without a ko.
This month's answer leans heavily on an email reply to the problem which I gratefully received from Tim Hunt.
Start by noting that had Black been able to play at 8 in Dia 1, he would have formed a comb formation which is known to be alive. Had White 8' been at the other 2-1 point would have met Black 9 at 8. We can therefore assume that White 8 in Dia 1 achieves something which harms Black.
We still can't say if the diagram is a success or failure until we know what the result of Dia 1 is and what other results are possible for Black in the original problem. If this is a ko, and other Black moves would have lead to death, then this would be a success. On the other hand, if other moves lead to life then this is a failure.
If Black plays 1, White 2 is a good move.
Black 3 is essential - should black play 3' which didn't remove a
liberty from White 2, then the White 4' would atari Black 1 et al and
capture them on the move after.
White 4 is atari on Black 3. If Black 5' connects to the left of 3 then
White 6' will also connect and Black would be unable atari from either
side due to shortage of liberties. (Even if he could it would be of to
no avail, the captured stones being a 4-stone T nakade shape.) Therefore
Black 5 must capture, starting the ko, (White to find the first threat).
Note that it is direct, either player can win by ignoring one threat and
capturing.
Can Black do any better than 1 in Dia 2?
If he draws back with 1' to 2 in Dia 2, White plays 2' at 1 and Black has a 2*2 nakade big eye - dead.
If he plays 1' at 5, things are more interesting - there being room for mistakes.
In Dia 3 Black dies unecessarily. In Dia 4 (6 at 
), he has to find
the first threat. So Dia 2 is better for Black.
I intended this problem to just be a discussion of the follow-ups to Dia 1 and the various kos involved. I realise now that as I phrased the question the original problem needs to be solved too! I refer you to Yang Yilun's book and quote Tim Hunt below...
I would describe the play in Dia 1 as unremarkable. Black tries to expand his eye-space with the obvious moves, and White tries to restrict it.
I don't think that White can do any better by varying from Dia 1.
Is Dia 1 good enough for Black? I can't see any way to just make more eye-shape. Therefore the interest must be in the cut of Black 1' at 2 and White 2' at 1 (in Dia 1), followed by a capturing race.
Naively there are 4 liberties to White and 2 to Black, so Black will have to make full use of his sente and whatever special-properties-of-the-corner or tesujis he can find. This doesn't seem to work.
So this just leaves using some clever move order, including the key cut later on. That is play one of the other moves in the 'ordinary sequence' such that if White answers it in the way necessary to get a ko to kill Black then Black can switch to a successful capuring race. Namely:
In Dia 5, White loses the capturing race, whilst in Dia 6 Black builds a 2 eyed live group.
So to answer the questions asked:
The diagram shown is an 'ordinary play' diagram which turns out to be a
failure for Black.
After Dia 1, the corner becomes a ko for Black to live.
What should have happened is that Black had a tesuji to live
unconditionally.
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Last updated 2004-08-10
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