Twisted four in the corner

    Keywords: Life & Death

A twisted four which occurs in the corner may not be quite the same as the normal twisted four. The twisted four in the corner follows exactly the same logic as bent four in the corner.

Table of contents


1. One or no outside liberties

[Diagram]

One outside liberty

If there are fewer than two outside liberties, White can turn this position into a ko.

[Diagram]

Main line

White 3 starts the ko. White can finish the ko by filling at black+circle.

note that after W3 a Black play at a is a self atari (or if there are no outside liberties a suicide)


2. Two or more outside liberties

[Diagram]

Two outside liberties

If there are at least two outside liberties, Black is alive with three points. (Three points instead of four because Black eventually needs an reinforcing move inside when White fills up one of the outside liberties.)

[Diagram]

Main line

Thanks to the two circle liberties, Black can play atari at B4. Without one of those liberties, he would be putting himself into atari.


3. Endgame implications

[Diagram]

Main line

When White reduces the outside liberties with W1, B2 makes three points in gote, preventing the ko.

Side note: B2 at a also lives, but is inferior to B2 because White would have a ko threat at B2.


4. Corner non-twisted four

The following is a Twisted Four and is in the corner but is not an example of what is meant by Twisted Four in the Corner. It is alive - a and b are miai:

[Diagram]

Not corner twisted four


See also:


Authors


This is a copy of the living page "Twisted four in the corner" at Sensei's Library.
(OC) 2016 the Authors, published under the OpenContent License V1.0.
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