This is a joint work with Renato Iturriaga.
We consider a Hamiltonian $H: \mathbf R^n \times \mathbf R \to
\mathbf R, \ (x,p) \mapsto H(x,p)$ that is $Z^n$ periodic in the
first variable $x$, and convex superlinear in the second variable
$p$.
For $...