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September 2002's Go Answer of the Month

Dia 1 - White to play.

Dia 1

This yose problem, from an Ishi press book, I feel to be very educational. It is one reason why I like the book a lot. (The reference will be given with the answer.)

To add a bit of original thinking, also determine Black's best yose here too.

The problem was taken from Ishi Press's Basic Techniques of Go (G2), page 152.

I wish to thank Tim Hunt for his help with the answers to this problem.

Dia 2 - The correct answer.

Dia 2 6 at triangle.

White 1 is a tesuji that isn't easy to spot - until you know it. Black's replies are forced. It is debatable whether White 7 or 7' at the 2-1 point on the top row is better - "G2" gives this diagram, but the 2-1 point removes sente moves for Black.

Dia 3 - White 1 as a hane is wrong.

Dia 3

White 1 as a hane is wrong, not because it fails, but just because it is around 8 points worse for White than Dia 2.

Dia 4 - White 1 at the 3-2 point?

Dia 4

After Black descends to 4, White is cut off in the corner and Black can capture 3 faster than White can capture 4.

If White plays 3' at 4, Black replies with 4' at 3 and the position ends up the same as Dia 3.

David Ward has pointed out that White can connect at the 2-4 point with 5 and then get a two-step ko. If white wins the kos he captures the black stones, so this is big. On balance this is probably still worse than the correct answer.

Dia 5 - In Dia 2, what if 4' at 5?

Dia 5 9 connects.

Playing this way Black ends in gote.

Dia 6 - If Black plays first.

Dia 6

It seems likely that the solid move of 1 here is correct. White will play 2 elsewhere since both the hane (to 5) and the descent (to 3) are gote. This gives Black the sente sequence of 3..6 later.

Black 1' at 3 is obviously wrong - experiment yourself.

Black 1' descending to 5 turns out to be gote with no followup (White 2' at 3, Black 3' at 1)

Other moves seem either worse, or at least no better for Black than Dia 6.

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