1. Ambrosetti, A. and Bessi, U. Multiple closed orbits for perturbed Keplerian problems. J. Differential Equations, 96 (1992), 283–294.
2. Ambrosetti, A. and Coti Zelati, V. Closed orbits with fixed energy for a class of N-body problems. Ann. Inst. H. Poincaré Anal. NonLinéaire, 9 (1992), 187–200 and 337–338.
3. Ambrosetti, A. and Coti Zelati, V. Periodic Solutions of Singular Lagrangian Systems. Birkhäuser, Boston, 1993.
4. Ambrosetti, A. and Tanaka, K., and Vitillaro, E. Periodic solutions with prescribed energy for some Keplerian N-body problems. Preprint. Scuola Normale Superiore Pisa, 1993.
5. Bahri, A. and Rabinowitz, P.H., Solutions of the three-body problem via critical point at infinity. Ann. Inst. H. Poincaré Anal. NonLinéaire. 8 (1991), 561–649.