Principles of affinity in nonlinear problems (Q1365700)

The authors give a survey on so-called relationship principles, i.e. conditions under which two different operators arising in the same kind of problem have related topological degrees. A classical source for such relationship principles is Chapter 3 of the book ``Geometrical methods of nonlinear analysis'' by the second author and \textit{P. P. Zabrejko} [Moscow: Nauka (1975; Zbl 0326.47052)].