Note: The abstracts of the short talks will be posted here in October.    Dr. Bart de Smit  (Universiteit Leiden, Netherlands) Escher and the Droste effect One of M.C. Escher's most intriguing works depicts a man standing in a gallery who looks at a print of a city that contains the building that he is standing in himself. This picture, with the title Print Gallery, contains a mysterious white hole in the middle. In a paper of Hendrik Lenstra and the speaker in the April 2003 issue of the Notices of the AMS it is shown that well known mathematical results about elliptic curves imply that what Escher was trying to achieve in this work has a unique mathematical solution. This discovery opened up the way to filling the void in the print. With help from artists and computer scientists a completion of the picture was constructed at the Universiteit Leiden. The white hole turns out to contain the entire image on a smaller scale, which in the Dutch language is known as the Droste effect, after the Dutch chocolate maker Droste. In the talk the mathematics behind Escher's print and the process of filling the hole will be explained and visualized with computer animations.    Dr. Stan Wagon  (Macalester College, St. Paul, Minnesota) Photo by C. Schofield Frozen Math: Sculpting Interesting Surfaces in Snow Since 1999 I have organized a team to compete at the Breckenridge International Snow Sculpture Championships. We have chosen mathematical and geometrical themes for our work and have had good success, with seven awards in eight years at this international competition. In this talk I will show how one goes about the extremely satisfying task of carving a smooth and complicated surface from a 20-ton, 12-foot-high block of compacted snow. This beautiful white material puts special demands on the design team since snow is not all that strong and can melt. But under the right conditions -- cold -- it is indeed strong and yields a wonderful medium for learning about both sculpting technique and the mathematics of some intriguing geometrical shapes. The designers of the shapes we have carved have been Helaman Ferguson, Robert Longhurst, Bathsheba Grossman, Brent Collins, Carlo Séquin, and David Chamberlain.   Back to the homepage:   www.mathsymposium.com