“…For this, we use the non-smooth critical-point theory of Chang [8] and an abstract three-critical-points theorem due to Bonanno and Marano [5]. We recall that such a three-critical-points theorem has been widely applied to large classes of nonlinear differential problems both in the regular case [3,4] and in the case of discontinuous nonlinearities [2,6]. Here, it is applied to differential systems, where the potential F is a nonlinearity that may be non-differentiable.…”