Minimizing coincidence numbers of maps into projective spaces

Ulrich Koschorke

Published 2006-06-01, updated 2009-04-12Version 2

In this paper we continue to study (`strong') Nielsen coincidence numbers (which were introduced recently for pairs of maps between manifolds of arbitrary dimensions) and the corresponding minimum numbers of coincidence points and pathcomponents. We explore compatibilities with fibrations and, more specifically, with covering maps, paying special attention to selfcoincidence questions. As a sample application we calculate each of these numbers for all maps from spheres to (real, complex, or quaternionic) projective spaces. Our results turn out to be intimately related to recent work of D Goncalves and D Randall concerning maps which can be deformed away from themselves but not by small deformations; in particular, there are close connections to the Strong Kervaire Invariant One Problem.