Black puts White's marked stone in atari, so White backs off with . After , White can't play at a as it would be auto-atari (but b is a ko threat). This isn't optimal play by White, though.
LukeNine45: This is how white responded in the actual game, which made me happy.
A ko fight ensues. White has to find the first ko threat.
LukeNine45: This is the solution I had in mind.
If white can't expect to win the ko fight, she still has the play at 4 for a little more profit later on. This won't work, of course, if white plays and loses the ko. ~Alex Baxter
LukeNine45: Does that work? I don't think it should. I know it didn't in the game, but I could have set the problem up wrong...
My goodness...totally missed that extra liberty. Nevermind =).
Mystery Go Player?: To show an alternative... is quite troubled. If we can assume that White has up to 5 big Ko threats elsewhere, Black can still win.
I know this sequence may seem a bit pointless and pedantic... However, the player needs to remember that an unreasonable play isn't always an impossible play. Simple forcing threats can result in endgame points. BEWARE!!!