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July 1998's Go Answer of the Month

Dia 1 - Status?

Dia 1

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.

Dia 2 - White to move.

Dia 2

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.

Dia 3 - Bad play by both players.

Dia 3

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.

Dia 4 - More bad play.

Dia 4

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.

Dia 5 - Good moves - a ko.

Dia 5

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.

Dia 6 - Seki.

Dia 6

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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