Kyu Exercise 121 / Solution

Analysis  

The placement at is a vital point, making miai of a and b, therefore White is guaranteed to capture either the single Black stone at the left side or the two Black stone on the right side.

It should be obvious that if White gets to play first, either White at a or b kills. However, if Black first, Black still can save his main group. However, the asymmetry in this problem is an important feature.

Black first: Solution  

If Black plays first, the solution is to connect on the right side with , and then descend with . Should destroys the eye at the bottom, captures the two White stone chain including .

Black first: Failure  

Connecting at the left side results in failure, because the extra exchange of and actually decreased Black's liberties, rendering ineffective. It is also not possible for to try to live by under the stones technique by playing at a, because at is sufficient to kill.