Perturbation of Hamiltonian Systems with Keplerian Potentials. Antonio Ambrosetti; V. Coti Zelati — 1989 Mathematische Zeitschrift
Addendum to closed orbits of fixed energy for a class of N-body problems A. Ambrosetti; V. Coti Zelati — 1992 Annales de l'I.H.P. Analyse non linéaire
Closed orbits of fixed energy for a class of N-body problems A. Ambrosetti; V. Coti-Zelati — 1992 Annales de l'I.H.P. Analyse non linéaire