# The Topology Seminar

## Spring 2009

**19th May: 10:15 - 12:00****, ****room 734, Sentralbygg II.**

Liz Hanbury: Simplicial Structures on Braid Groups and Mapping Class Groups

**Abstract:** *The homotopy groups of spheres are notoriously hard to calculate. In this talk I will explain how simplicial methods have been used to give descriptions of the homotopy groups of S*^{2}. I will review some recent results in this area (of Jie Wu, Fred Cohen and others) and talk a little about my joint work with Jon Berrick and Jie Wu.

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**24th February: 10:15 - 12:00****, ****room 656, Sentralbygg II.**

Tore A. Kro (Sarpsborg): Stratified Spaces

**Abstract:** *We will construct certain stratified spaces inside the category of Frölicher spaces. Various ways of generalizing the notion of tangent space for a manifold will be discussed. For different purposes all of the following seem relevant: Flow spaces, curve spaces, ray spaces and continuous derivations. The differences between these will be illuminated by basic examples. We will introduce type A and type B embeddings and prove that the image of a locally compact sharp stratified space under a type B embedding into an Euclidean space naturally gets the structure of a Whitney stratified set. Furthermore, I will indicate an approach to Thom's first isotopy lemma.*

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**## Seminars given the previous Spring

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