Periodic solutions for differential inclusions in ${\Bbb R}^N$

summary:We consider first order periodic differential inclusions in $\mathbb {R}^N$. The presence of a subdifferential term incorporates in our framework differential variational inequalities in $\mathbb {R}^N$. We establish the existence of extremal periodic solutions and we also obtain existence results for the “convex” and “nonconvex”problems