Babytop

Student seminar in topology

Fall 2005






Tyler Lawson
The Plus Construction

Abstract:

The plus construction is a (homotopy invariant) construction we apply to connected spaces where pi_1 contains a perfect normal subgroup. It has several descriptions and is related, for example, to Bousfield localization with respect to integral homology. The Kan loop group functor G(X), however, gives an equivalence between the homotopy category of reduced simplicial spaces and the homotopy category of simplicial groups, so there must be an expression of the plus construction in terms of simplicial groups. In these circumstances, integral homology is replaced by Quillen homology. In this talk I will introduce the plus construction, discuss the version for simplicial groups, and talk about how this generalizes to other kinds of objects such as simplicial rings or other "ring objects".