Beginner Exercise 26 / Solution

Solution  

This bent four shape has a serious weakness: the cutting point at a and the marked stones without outside liberties. makes miai of the snapback at a and destroying the eye at b.

continued  

After , is atari reducing Black's eye space. If Black defends with , then kills. If the marked stones had one or more outside liberty, Black could live by playing at instead.

Failure 1  

is an example of a bad atari which should not be played. connects, and now a and b are miai, so Black lives.

Failure 2  

is met by (or a) to secure two eyes.

(For advanced readers: is slightly better than a because Black has two ko threats here after two successive White moves, which are possible in a ko fight)