Home > Steve > Go > Problem of the month
(There was no problem in December 2002.)
This turned up in a 13*13 game I played at the Cambridge small-board tournament against a 3 dan. My handling of the corner was not all it should have been and my opponent was surprised I didn't know it.
So this month's problem. Black to play to attack the white corner.
I have to start by confessing that I still don't know the answer to this and that it has turned out to be far trickier than I expected. In addition I have failed to find this discussed in a book - so I have no authoritative answer.
Note that the question is attack the corner, not kill the corner. White can be expected to live, but his score must be minimised.
The 3 dan tells me that a Black hane at the 4-1 point is wrong and that the correct answer is a black play at the left side 1-2 point. As yet I cannot confirm this. I do present what I have found out about the incorrect hane. Note that many of the sequences presented are relevant to the correct attack, but ...
Dia 2 contains the obvious moves which are poor in many cases! This sequence is worth 6 points to White with Black retaining sente.
Working backwards from the finish:
White 6 in Dia 2 is right otherwise Black 7 can force a ko fight for the life of the group. After 11 White cannot squeeze the two black stones in the corner at the 1-3 point due to a shortage of liberties. He also cannot connect the two white stones in atari. He has to capture 11 and then 7 in a direct ko to live. This is unnecessarily painful for White.
Black 5 in Dia 2 is not a wrong move, it is however premature. There is nothing that White can do if Black doesn't play this and since 6 there is a forced reply, it would be better kept for later as a ko threat with Black 5' elsewhere.
Note that if Black chose to play 5 as in Dias 4 & 5, White 6 must be at the 2-2 point to prevent the seki of Dia 4. Dia 5 is still 6 points to White in Black's sente.
If White 4' in Dia 2 were a tenuki, Dia 6 reduces White's corner to 3 points (2 in the corner and 1 net prisoner). So White must have found a move worth more than these 3 points.
Dia 7 - Black 3' gets a ko to kill.
If Black plays 3' as Dia 7, he can get a ko to kill the entire corner - compare with Dia 3. Because White doesn't like this, White 2 in Dia 2 was wrong.
If White 2' defends as Dia 8, then he gets an undisputed 5 points in the corner and Black takes gote.
As I said at the top, Black 1' at 2 in Dia 8 has yet to be properly researched. However the few sequences here have proven hard to sort out. I hope to return to this problem at a future date.
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Last updated 2004-08-10
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