Gokyo Shumyo, Section 1, Problem 12 / Solution

First move  

There is absolutely no time to expand the eyespace. White has to play at the vital point right now. And the vital point of this shape is .

Full line  

The points and are miai and after the 2-3 exchange, a and b are miai.

Why the vital point ?  

The reason that is the vital point lies in the fact that White can answer the atari of with . Without in place, Black would capture three stones.

Wrong  

As said before, expanding the eyespace is not right. Black plays atari at and after , Black can start a ko with at . Life in ko is not sufficient.

Wrong (ii)  

This shape does not call for the 1-2 point. The points a and b are miai to keep White down to one eye, and Black destroys the other eye by playing .

Playing at b also works. Black should not play the atari as in the previous diagram, because that permits ko. In fact, destroys more eye shape than it makes and she dies unconditionally.

Wrong (iii)  

After here, Black can kill unconditionally, without a ko. After , White cannot make a second eye due to shortage of liberties. If at , at is a deadly eye shape destroyer.

Wrong (iv)  

here leads to the same tesuji of to create shortage of liberties.

First move  

here doesn't work either... kills immediately.