Home > Steve > Go > Problem of the month
This is another status problem - life and death questions again.
This situation turned up in a game between two club members earlier
this month. After a fair bit of analysis, we (the club) reckon we
understand it, but it isn't as simple as it looks.
Answers from strong dans welcome.
Meanwhile I have received a quality e-mail from Tim Hunt providing a fairly in depth analysis. Much of this answer is based on his information - Thank you Tim.
Being a status problem, let us address white to move first, it is "obvious" that white can live by playing at the 2-2 point. It turns out that a play as Dia 2 is best though.
Black 2 is a good ko-threat / 1 point sente yose move. In this case, White gets 12 points in the corner.
For completeness, White can play 1' at 1, 3, or any + and live.
Now for Black. Any Black 1 except at the 2-2 point permits White to live with territory. Let's look at this 2-2 point then.
During the investigation after the club game, it was the discovery of this 5-point 'gun' nakade - which leads to white killing black only to find himself with just one eye and so dead - that caused the interest in the shape.
In order to prevent the nakade, White plays 4 here and in this sequence we get a ko for life.
Have you spotted the bad play in Dia 4? Black 5' should be at 7 immediately. That prevents white 6, so the best 6' is below, on the 3-1 point. But then Black plays 7' at 5 and White is out of liberties and cannot place black in atari. In due course, Black can atari white from the outside.
It turns out that attempting to make an eye with white 2' in Dia 3 was a mistake. The best white 2 is the 1-1 point here which leads to a direct ko.
There are a couple of other ways of reaching a ko, mostly equivalent.
And lastly, if Black has no ko threats at all, he can play for a seki instead.
White can kill.
Black can live in ko or a gote seki at his choice.
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British Go Association
Last updated 2004-08-10
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