Generalized Lefschetz numbers of pushout maps

There is a useful way of defining a new map ƒ from other given maps ƒA, ƒ1 and ƒ2: the pushout construction. The pushout map ƒ 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 ƒ to those of the given maps ƒA, ƒ1 and ƒ2. 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.