[Binghamton Geometry/Topology Seminar] Topology/Geometry Seminar next Tuesday Oct 13 (Joint with Algebra seminar)

[Tam Nguyen Phan]

BINGHAMTON GEOMETRY/TOPOLOGY SEMINAR (joint with Algebra seminar)

   Date: Tuesday, October 13th, 2015

   Time:  2.50 pm

   Place: Whitney Hall, Room 100E,  followed by coffee/tea in the
      Hilton Reading Room. Note the new location of the math department (
http://www2. <http://www2.math.binghamton.edu/p/directions>
math.binghamton.edu <http://www2.math.binghamton.edu/p/directions>
/p/directions <http://www2.math.binghamton.edu/p/directions>).

   Speaker:  *Robert Bieri* (Binghamton University)

   Title:  *Groups of piecewise isometric permutations of lattice points*

    Abstract: An orthant (of the orthogonal integral lattice)

 is the image of the standard orthant  under an affine-orthogonal
transformation. And a permutation  of a subset   is
piecewise-Euclidean-isometric (pei), if  is a disjoint union of finitely
many orthants, , on each of which  restricts to an isometric embedding . I
will talk about the group  of all pei-permutations of various subsets  and
its subgroup  of all piecewise-Eucliden-translation permutations. In the
case when  consists of the lattice points on the union of  positive
coordinate axes then  is the Houghton group .

This is joint work with Heike Sach: we prove finiteness properties of some
pei- and pet- groups, and have, as a consequence, that  admits a
K(G,1)-complex with finite -skeleton.

An interesting point is that prominent groups like Richard Thompson's
group  crop
up when we extend the consideration to the -lattice in the hyperbolic plane.



NOTE:  The seminar has a webpage where the semester's program is listed:

http://www2.math.binghamton.edu/p/seminars/topsem
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