1. A. Ambrosetti and V. Coti-Zelati, Critical points with lack of compactness and applications to singular dynamical systems, preprint.
2. Periodic solutions of singular dynamical systems;Ambrosetti,1987
3. V. Coti-Zelati, Morse theory and periodic solutions of Hamiltonian systems, preprint, SISSA, Trieste.
4. Periodic solutions of dynamical systems with Newtonian type potentials;Degiovanni,1987
5. C. Greco, Periodic solutions of a class of singular Hamiltonian systems, Nonlinear Anal., in press.