Alex Weldon: This situation arose in the final game of an informal little tournament I played on KGS. I was White, and "dkiller" (a 5k from France) was Black. The edges of the board are nowhere in sight. Consider all stones at the edges of the diagram to be part of living groups. The problem is for White to capture all the Black stones in the middle. In the game, I played a, which let Black get a ko. Afterwards, I tried playing with b and c, thinking that one of them would let White kill unconditionally, but still, the best I could come up with is ko. I've discovered too many variations to put them all here, so I'll leave it up to others to play around and see what they can find.