[Binghamton Geometry/Topology Seminar] Nov 17

[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:* Robert Bieri (Binghamton University and Goethe University
Frankfurt)
*Title: *Isolated and Condensation points in the space of marked groups***

Abstract:*  The set G(m) of all isomorphism classes of m-generator groups
can be identified with the set of all normal subgroups S of the free group
F of rank m. G(m) is endowed with the CHABAUTY-topology, which is based on
the sets of all S containing one and avoiding a second given finite subset
of F. It is a remarkable fact that whether a group G in G(m) is isolated,
or is a condensation point - or, for that matter, any other local property
of the point G in G(m) - is independent of the generating set of G and of
m; hence those are group theoretic properties.
I will present examples and condensation criteria, one of which is best
understood in terms of the Geometric Invariant Σ(G) from joint work with
Walter Neumann and Ralph Strebel. The presented work is a joint work with
Luc Guyot, Yves de Cornulier and Ralph Strebel.
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