Beginner Exercise 278 / Solution

Solution  

makes a placement in the middle of the farmer's hat. However, Black is not unconditionally dead, because and can start a one-move approach ko.

Approach ko  

The one-move approach ko works as follows. If Black wins the initial ko fight, then if Black wants to live then he needs to fight the same ko again by playing at . Subsequently, if Black wins the second ko, he lives with two eyes by capturing at a.