“…A rich literature is available by now on problems with discontinuous nonlinearities, and we refer the reader to Alves, Bertone and Gonçalves [1], Alves and Bertone [2], Alves, Gonçalves and Santos [3], Ambrosetti and Turner [9], Ambrosetti, Calahorrano and Dobarro [10], Badiale and Tarantelo [11], Carl, Le and Motreanu [21], Clarke [26], Chang [19], Carl and Dietrich [22], Carl and S. Heikkila [23,24], Cerami [25], Hu, Kourogenis and Papageorgiou [40], Montreanu and Vargas [44], Radulescu [47] and their references. Several techniques have been developed or applied in their study, such as variational methods for nondifferentiable functionals, lower and upper solutions, global branching, fixed point theorem, and the theory of multivalued mappings.…”