Title: Group Actions and Helly's Theorem
Speaker: Professor Benson Farb
Speaker Info: University of Chicago
Brief Description:
Special Note:

In 1973 Serre proved that any action of the group SL(3,Z) on a tree must have a global fixed point. He deduced from this a number of beautiful results about splittings of groups and integrality of representations.

In this talk I will describe a higher dimensional generalization of Serre's theorem (which is the one-dimensional case), and will explain its implications in representation theory and combinatorial group theory. The main idea is a connection between the combinatorics of generators for certain matrix groups and the combinatorics of Helly's 1913 theorem on convex sets.

This talk should be understandable to first year graduate students.

Date: Friday, April 06, 2001
Time: 4:00pm
Where: Lunt 105
Contact Person: Prof. John Franks
Contact email: john@math.northwestern.edu
Contact Phone: 847-491-5548
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