Solution by lavalyn 17k
This is not exactly tsumego as there appears to be more than one solution.
Dieter: Correct, but there is a two point difference between them. You can see it as a test whether you check all possibilities even if you found one that "works".
Now a and b are miai for life.
Disconnected bent four but not disconnected sufficiently to kill.
Black 3 is not necessary.
If Black really wants to have a group killed.