A detailed look at the Szczarba map

Abstract

We explain how to derive an explicit formula for a natural transformation relating the (left adjoints of) the homotopy coherent nerve and the Dwyer-Kan simplicial classifying space functor. The formula is derived using a method introduced by Szczarba when comparing two different chain models of a fibration. This note may be taken as a companion to section 3 of our previous article "Categorical models for path spaces".