If White pushes at a, Black responds at b.
This is my first solution, hope I got it right... -phooky
lavalyn: Excellent work. Except that Black need not respond to a or b - either play by White and she dies in gote. Notice that to capture the three black stones requires both a and b - at which point she has only one liberty left. Thus White dies in shortage of liberties.
demetria wonders: Wouldn't white be more likely to respond with at . Also wouldn't black answer the original by setting up the ko first?
Roger is confused. Sorry if I'm just a newb, but I don't see how Black can actually make the kill, if White plays at 'b'? Any move Black makes will get his center stones killed. The only option I can see is for him to go for a ko fight at e1.
Dan: Here is the situation after White plays at b in the previous diagram. As you said, Black dies if he makes a move... so he tenukis. White can't approach on either side (at a or b) without putting his own stones in atari. Eventually B could play at c and d (waiting until there are no ko threats if necessary) and pick up the White group, so it is not seki.
Bill: It's worse than that. In theory, bent four could be fought with ko threats. Here, no finite number of ko threats helps White, as Black could exhaust White of them. The parallel is with moonshine life.
I think this is a reasonable response that would leave white with only false eyes. White might be able to live with a very small eye if it takes first, but it looks like there'd be too little to gain.
Quacki: I thought about this to be the solution, but white gets a ko after this one (Which I did not see until after I saw the solution).