Xuanxuan Qijing Problem 13 / Solution

Solution is two stage ko  

The best solution for both players is to give White a two-stage ko, enabled by the throw-in of .

Black captures throw-in.  

If Black captures the throw-in, then White can get another, better ko (see "Black chooses 'a' 1" & "Black chooses 'a' 2").

Cont. -  

White exchanges for and then performs the key probe of . Black's reply at a, b, and c will be demonstrated.

Black chooses 'a' 1.  

@ 4. White makes a ko.

Black chooses 'a' 2.  

White still makes ko.

Black chooses 'a' 3.  

White lives unconditionally.

Black chooses 'b' 1.  

White lives unconditionally.

Black chooses 'c' 1.  

White lives unconditionally.