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Joseki-related life-and-death example 1
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    Keywords: Joseki, Life & Death

Joseki

[Diagram]
Joseki.

This is a common 4-4 point joseki.


[Diagram]
Joseki.

W3 can also be played at a. B4 ends the joseki.



Discussion I

[Diagram]
White is alive.

The group in the corner is alive, as discussed in L+2 group.

However, a black descent at a is sente.[1]


[Diagram]
Ko.

If White tenukis, Black can start an approach ko with the sequence from W1 to W5.


[Diagram]
Dead.

The atari at W4 is a mistake. After B7, white is caught in a shortage of liberties and is unable to play at a.



Discussion II

[Diagram]
White is alive.

In this diagram, White is alive too. (Is there any existing material that discusses this J+1 group?)

However, the descent at a is sente.[2]


[Diagram]
Dead.

The throw-in at B1 followed by the placement at B3 is the tesuji. After which, a and b are miai, while c and d are also miai. White dies in a bent four in the corner dead shape.



Author:


[1]

I'll comment that, because Black's threatened ko is indirect, one cannot assume it is really sente until the latter stages of the game. This may affect fighting on the outside.

Charles

[2] Note however that it is usually an endgame mistake to play the descent. Instead, Black should start at b.



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