Mathematics Colloquium: Vogtmann Abstract, Spring 2004

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Mathematics Colloquium, Spring 2004

Karen Vogtmann
Cornell University

Finding invariants of Outer space

The group Out(F_n) of outer automorphisms of a free group can be realized as the group of symmetries of a certain geometric object called Outer space. Invariants of Outer space, and of its quotient by the action of Out(F_n), are often algebraic invariants of the group itself. In this talk I will describe outer space and show how to find non-trivial invariants, which can be described in terms of finite graphs. These invariants were originally defined by S. Morita, in terms of a certain infinite-dimensional Lie algebra.

Thursday, April 29, 2004, 245 Altgeld Hall, 4:00 p.m.

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