I give a one-hour introduction to the complexity class PPAD. Mostly done on the blackboard but using the laptop to show some nice depictions of Sperner's lemma. A nice talk today was by Martin Hoefer on pricing edges in a graph for buyers who want to obtain spanning trees; it started out with examples that explained the scenario very nicely. Another talk I liked was Uri Zwick (on Monday) on introduction to parity games and related games; it was very informative.
Later, I distribute some flyers for COMSOC-2008. I play some pool and ping-pong.