[Binghamton Geometry/Topology Seminar] Dec 8 (last seminar this semester)

[Dmytro Savchuk]

                   BINGHAMTON GEOMETRY/TOPOLOGY SEMINAR

*Date:*  Thursday, Nov 17, 2011

*Time:*  2:50-3:50pm
*Place:*  Library North 2205 followed by coffee/tea in the Anderson Reading
Room.

*Speaker:* Tim Riley (Cornell University)
*Title: *Hydra groups*

Abstract:*  I will describe some wild geometry that arises in an apparently
benign group theoretic setting: I will exhibit a family of groups that are
CAT(0), bi-automatic, 1-relator, and free-by-cyclic, and yet have free
subgroups of huge (Ackermannian) distortion. I will show how these lead to
examples of hyperbolic groups with finite-rank free subgroups of similarly
huge distortion. The origin of the extreme behaviour lies in a simple
computational game - a realisation of Hercules' battle with the hydra,
played out in manipulations of strings of letters.
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