Brian: Here's my guess.
To me, it seems that after , Black has an eye somewhere at a and a second eye somewhere at b.
Velobici: is not right. While Black can form an eye to the left of , there is no eye to the right. White can push in from the outside on the right preventing Black from forming an eye there. (This was my error in the lesson, prompting me to believe that this might be a good problem for TsumegoFromGames.)
I've tried and I've tried, but Black is alive with that move. SUGOI desu ne!!!