Gokyo Shumyo, Section 1, Problem 18 / Solution

Main line  

comes in handy when gives atari and threatens to make two eyes. If White connects at , Black captures at a and has an eye in the corner and one where he captured four stones.

Variation 1  

takes a vital point, and and reduce the eyespace but still a and b are miai for life.

Wrong (seki)  

creates a long L group, leading to seki. Life with points as in the correct diagram is better than seki.

Wrong (White mistake)  

If White resists at , is a tesuji. recaptures at and if White connects underneath at a, Black can give atari at b.

Wrong and (ten thousand year ko)  

Here Black misses the tesuji and ends up with a ten thousand year ko.

Wrong 2  

is badly placed for catching the clamp stone .

Addendum  

If the marked stone is present doesn't work anymore. is double atari.

Addendum  

In this case it is better to create a long L group with 1. The marked stone now alters the status from seki to ten thousand year ko. See Long L Group for details.