The clamp of is the solution. The strongest resistance black can try is a; b creates too many cutting points.
( at )
After , white has a or b.
Therefore, Black tries here. The sequence to follows.
Next white tries to capture the three black stones. Notice is threatening to play at and make life with a. Were White to play at , she would have miai of playing at a and capturing the two marked Black stones. Black destroys White's eye with . After , Black can't escape.