Two by four box

    Keywords: Life & Death

1. No outside liberties

[Diagram]

No outside liberties

If there are no outside liberties, White can make a sente seki.

[Diagram]

Main line

W1 is the strongest attack. B2 is the vital point. B6 is necessary or White plays there (or to the right of it) to capture the corner.

[Diagram]

Variation at 4

If B4 here, W5 makes a thousand year ko. This result is generally worse for Black than a seki.

[Diagram]

Variation at 2

B2 at the 2-2 point invites another thousand year ko.

[Diagram]

Variation at 2 - White's mistake

W5 in this variation spoils the chance of a ko and invites a seki.


2. Outside liberties

[Diagram]

Outside liberties

If there is at least one outside liberty, Black is alive with seven points.

[Diagram]

Main line

Now B2 and the throw in at B4 work. B6 creates shortage of liberties for White. (If there were no outside liberty, B6 would be self-atari.)


Conclusion for the endgame

[Diagram]

Outside liberties

W1 threatens to destroy seven points in sente (assuming capturing the corner would decide the game). B2 makes seven points in reverse sente. So,



W1 is a typical ko-threat - but it is a bad one. In case of a ko the previous diagram supplies four ko-threats: that's one more than here.


This is a copy of the living page "Two by four box" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.
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