Generalized Lefschetz numbers of pushout maps

There is a useful way of defining a new map f from other given maps fA, f1 and f2: the pushout construction. The pushout map f is analogous to the well known pushout of topological spaces. In this paper we prove a Pushout formula relating the generalized Lefschetz number of the pushout map / to those of the given maps fA, f1 and f2. This provides a tool to compute generalized Lefschetz numbers and Nielsen numbers in a rather easy way. Some interesting examples are given at the end of the paper. © 1996 elsevier science B.V. All rights reserved.