On second order discontinuous differential equations in Banach spaces.
Notions as the numerical range and the spectrum of couple of homogeneous operators on a Banach space are used to derive theorems on solvability of the equation Conditions for the existence of eigenvalues of the couple are given.
The existence of positive solutions for a nonlocal boundary-value problem with vector-valued response is investigated. We develop duality and variational principles for this problem. Our variational approach enables us to approximate solutions and give a measure of a duality gap between the primal and dual functional for minimizing sequences.