KyuExercise169/Solution

 

seems soft, but it is the correct move. Black's attempts to create eyespace with and are met with strikes at the vital points of and . tries to create an eye at a, but strikes at black's shortage of liberties.

 

This fails even more quickly when makes miai of a and b.

 

If black plays the vital point instead, thinking your opponent's good move is your good move, white throws in with to set up an atari with . White can play this to set up shortage of liberties, or at to connect out.

 

or at a fail because after captures the marked stones, black is left without enough eyespace.

Best Defence  

is the best defence and leads to a ko for life.