Ko Lock

  Difficulty: Advanced   Keywords: Tesuji, Ko, Shape, Tactics
After the cross-cut  

For White to play white+circle in reply to Black's cut here is a standard piece of shape. White has a good reply to Black a atari.

Ko lock (i)  

If B1, W2 is double atari and B3 is forced.

Ko lock (ii)  

White plays W4 relying on being able to capture at a in sente, forcing Black b. Since there are proverbially no ko threats in the opening, White's plan will very often work and build influence.

After the cross-cut  

Therefore Black usually[1] extends to B1 (or a - the choice isn't straightforward): W2 next leaves White's marked stone on a good point for shape.

Bildstein: But what is ko lock? Six good and six bad shapes says it is one of the six 'famous good shapes'. This page gives an example, and I can follow the logic of the example to see why it is reasonable play, but I can't tell what it's getting at more generally.

kokiri - in the example, white denies black access to the centre of the board by setting up the ko shape. I think this act of locking black into the side is the point, so white is unworried about winning the ko

This tactic is as old as the hills; but the 'ko lock' name goes back to Victor Chow, a Chinese amateur now in South Africa.

Charles Matthews

[1] Actually it seems that the atari is also current in pro games, while the extension to a isn't.
TDerz Isn't there an Ishida game (1992 Honinbo) where one player plays the tesuji 3 times, the other stubbornly captures three times the stone?

Ko Lock last edited by Dieter on November 5, 2007 - 16:07
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