char: Heh, you caught me; I got the idea of this problem from those classical problems. I will post the rest of the comments below Herman Hiddema's solution.
Herman Hiddema: After , black can live by playing a. However, the question was for white to make black alive, not to make the situation unsettled. So suppose we allow white to play at a, the question then is:
Herman Hiddema: The simple way.
Herman Hiddema: The harder way.
First of all, the problem might as well be like this.
On the second thought, since the "worst move" problems has a pretty high attempting/solving rate compare to other problems on SL, I decided to sneak more information in the problem ^^