Two topological definitions of a Nielsen number for coincidences of noncompact maps
© Andres and Väth 2004
Received: 25 August 2003
Published: 3 March 2004
The Nielsen number is a homotopic invariant and a lower bound for the number of coincidences of a pair of continuous functions. We give two homotopic (topological) definitions of this number in general situations, based on the approaches of Wecken and Nielsen, respectively, and we discuss why these definitions do not coincide and correspond to two completely different approaches to coincidence theory.