BeginnerExercise193/Solution

Solution  

After , black is alive. If white plays at a, then black can safely tenuki and is still alive.

Not a ko  

If white plays here, then black replies at and lives unconditionally.

Failure  

If black plays here, then after , black must play to live. This is a seki, so black has less territory than in the solution diagram. Alternatively, black could play at a to make a ko, but that's generally a bad idea. (The difference between this and the previous diagram is the liberty at b.) See /Discussion for more details.