Solution  

After the black group is alive. at a is the most interesting attempt White has, but we will also take a look at at b, c, and d.

Resistance 'a'

Continue  

and can be switched.

After dead stones are removed  

Black has x or y to make two eyes.

Resistance 'b'

 

is important to prevent bulky five eye shape.

Resistance 'c'

 

Resistance 'd'

 

In Resistance 'a', if Black forgets to capture with r first, the atari at x doesn't work anymore.