Home > Steve > Go > Problem of the month

September 2000's Go Answer of the Month

The basis for this problem was presented in a twenty year old Go World. A related problem is also in Yutopian's "The Art of Capturing".

Dia 1 - White to play.

Think carefully, this problem is not as straight-forward as it may at first appear.

It is likely that this problem will have been correctly answered by both weaker players and stonger ones. It is mid-range players who may get it wrong.

Dias 2 & 3 - A tesuji.

 
14 at .

White 1 is a standard attacking move at a vital point. It is one that in many related situations can kill Black, however here Black has a tesuji reply to survive.

Black plays 4 to force White into an "under the stones" shape and sacrifices the four stones, using the time gained to make one eye with 12. After White captures with 13, it becomes apparent that Black can play 14 back in at .

Many of the moves in Dias 2 & 3 are forced.

I am taking the opportunity here to discuss the various moves in the sequence that lets Black live...

• White 1: A vital attack. Of course as it fails this whole sequence is not recommended!
• Black 2: Obvious. The other possibility of 2' at 3 gets 3' at 2 and then Black cannot atari the white stones due to a shortage of liberties. He has insufficient room / time for two eyes on left part of the group alone.
• White 3: Standard procedure.
• Black 4: A tesuji. Black 4' at 7 fails - see Dia 4.
• White 5 reduces Black's eyespace.
• Black 6: Black's left half is short of liberties. 6' cannot be played at 7, since white would reply with 7' at 6. Black cannot then block 'right-of-6' and has to capture for an eye in the corner. However White 9' would play there ('right-of-6') and hence stop a second eye.
• White 7 prevents Black 8' 'left-of-7' and hence gains some time for White.
• Black 8: Because Black has to capture two stones with 8.
• White 9 encourages Black to make a mistake.
• Black 10 is correct. Playing 10' at 12 to gain an eye immediately would fail to White 11' left-of-8. Another shortage of liberties stopping Black in his tracks.
• White 11: If 11' at 12 to stop that eye, Black captures four stones in a row for two eyes.
• Black 12: Another key move. This forms one of the two eyes and sacrifices the four right-side stones.
  Playing 12' at 13 to capture the four white stones fails as shown in Dia 5.
• White 13 captures.
• Black 14 plays back in with an atari which captures the five white stones for the second eye.

Dia 4 - How not to play Black 4.

7 at 1, 8 captures at 3,

After White 9, Black cannot get an eye in the corner and again there is insufficient room on the left for two eyes. Black dies.

Dia 5 - How not to play Black 12.

13 at , 14 at ,

As shown here, White 13 sets up a snapback forcing 14. If Black ignores this to play at 15, then White 15' at kills Black. If Black plays 'left-of-', White ataris 'right-of-', still killing Black.

Anyway, Dias 2 & 3 fail for White so he best not play them.

Go World 28 puzzled me for a long time by showing this as the answer diagram. I think they must have misphrased the question - "How should Black refute White 1" would have made more sense.

Dia 6 - The correct answer.

Therefore White just plays the 'boring' reduction of 1 to 4 in sente.
White should not play A, Black B, White C as it is a gote sequence worth only one point. Therefore Black A, White C is Black's privilege for a corner worth 6 points.

Had White played as Dias 2 & 3, Black's corner would be worth about 13 points.

Home > Steve > Go > Problem of the month
British Go Association
Last updated 2004-08-10
This page is part of http://www.stocton.org/
Email: webmaster@stocton.org