Did anyone go to Knuth's talk at MathFest this past weekend? It sounded interesting, but I wasn't able to go and couldn't find a write-up on the web; I'm hoping one of you can summarize. Here's what's on the web: PI MU EPSILON J. SUTHERLAND FRAME LECTURE NEGAFIBONACCI NUMBERS AND THE HYPERBOLIC PLANE Donald E. Knuth, Stanford University, Professor Emeritus of the Art of Computer Programming Saturday, August 4, 8:00 pm - 8:50 pm All integers can be represented uniquely as a sum of zero or more "negative" Fibonacci numbers F-1 = 1, F-2 = -1, F-3 = 2, F-4 = -3, provided that no two consecutive elements of this infinite sequence are used. The NegaFibonacci representation leads to an interesting coordinate system for a classic infinite tiling of the hyperbolic plane by triangles, where each triangle has one 90 degree angle, one 45 degree angle, and one 36 degree angle. Jim Propp