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Ko Lock
  Difficulty: Advanced   Keywords: Tesuji, Shape, Tactics

[Diagram]
After the cross-cut

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


[Diagram]
Ko lock (i)

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


[Diagram]
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.


[Diagram]
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.



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.



This is a copy of the living page "Ko Lock" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.