On the solvability of systems of inclusions involving noncompact operators

We consider the solvability of a system, of set-valued maps in two different cases. In the first one, the map (x, y) −F(x, y) is supposed to be closed graph with convex values and condensing in the second variable and (x, y)− G(x, y) is supposed to be a permissible map (i.e. composition of an upper semicontinuous map with acyclic values and a continuous, single-valued map), satisfying a condensivity condition in the first variable. In the second case F is as before with compact, not necessarily convex, values and G is an admissible map (i.e. it is composition of upper semicontinuous acyclic maps). In the latter case, in order to apply a fixed point theorem for admissible maps, we have to assume that the solution set x − S(x) of the first equation is acyclic. Two examples of applications of the abstract results are given. The first is a control problem for a neutral functional differential equation on a finite time interval; the second one deals with a semilinear differential inclusion in a Banach space and sufficient conditions are given to show that it has periodic solutions of a prescribed period. © 1994 American Mathematical Society.