The degree theory for set-valued compact perturbation of monotone-type mappings with an application

Degree theory has been developed as a tool for checking the solution existence of nonlinear equations. Hu and Parageorgiou [S.C. Hu, N.S. Parageorgiou, Generalisation of Browders degree theory, Trans. Amer. Math. Soc. 347 (1995), pp. 233259] generalized the results of Browder [F.E. Browder, Fixed point theory and nonlinear problems, Bull. Amer. Math. Soc. 9 (1983), pp. 139] on the degree theory to mappings of the form f+T+G, where f is a bounded and demicotinuous mapping of class (S)+ from a bounded open set in a reflexive Banach space X into its dual X*, T is a maximal monotone mapping with 0T(0) from X into X*, and G is an u.s.c. compact set-valued mapping from X into X*. In this article we continue to generalize and extend the results of Browder on the degree theory to mappings of the form f+T+G. By enlarging the class of maximal monotone mappings and pseudo-monotone homotopies we obtain some new results of the degree theory for such mappings. As an application, an existence result of solutions for generalized mixed variational inequalities is given under some suitable conditions.