Rectangular Eight In The Corner

    Keywords: Life & Death

Table of contents

1. No outside liberties

[Diagram]

No outside liberties

This position is hyperactive. Its value and play depends upon the ko threat situation. If White is komaster she can often make seki with sente.

[Diagram]

Sente seki

W1 is the strongest attack. B2 is the point to avoid ko. 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 ten thousand year ko. This result is generally worse for Black than a seki.

[Diagram]

Variation at 2

B2 at the 2-2 point invites an approach ko.

[Diagram]

Variation at 2 - White's mistake

W5 in this variation invites a seki. Without B6 either player can make a throw-in ko.


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 works. The throw in at B4 and B6 are oiotoshi. (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. 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.


See also


This is a copy of the living page "Rectangular Eight In The Corner" at Sensei's Library.
(OC) 2007 the Authors, published under the OpenContent License V1.0.
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