Gokyo Shumyo, Section 1, Problem 26 / Solution

Main line  

The tesuji here is . After , Black can't create a dead shape with a, because he is in shortage of liberties (this is oshitsubushi). Note what a difference a black stone on the marked point would make.

Variation 1  

White has to be careful to answer at and not at . The strength of is precisely that it already prevents the connection underneath.

Variation 2  

Answering at is the only move. It appears as if White can destroy the eye after this sequence by throwing in again at , but White will simply connect at a.

Variation 3  

After , a and b are miai. (If Black tries to leave White with a big eye by connecting at a (almost filling the enclosed space with the dead shape of three in a line), White runs to b and gets a second eye at c.)

Variation 4  

After, , doesn't work, as is shown by this diagram.

After , a and b are miai.

Wrong 1  

Black's hane produces a ko

Wrong 2  

Black kills with the same hane.

White lives?  

After , can white live?

White lives  

Why not the simple descent of ? This makes miai of a and b, no?