Existence of three nontrivial solutions for nonlinear Neumann hemivariational inequalities

In this paper we consider a nonlinear Neumann problem driven by the pp-Laplacian with a nonsmooth potential (hemivariational inequality). Using minimax methods based on the nonsmooth critical point theory together with suitable truncation techniques, we show that the problem has at least three nontrivial smooth solutions. Two of these solutions have constant sign (one is positive, the other negative).