1. Periodic solutions of Lagrangian systems on a compact manifold;Benci, Vieri;J. Differential Equations,1986
2. [2] J.K. Beem, P.E. Ehrlich: “Global Lorentzian Geometry", Pure and Applied Mathematics, Marcel Dekker Inc., NY, 1981.
3. [3] V. Benci, D. Fortunato: Periodic trajectories for the Lorentz metric of a static gravitational field, Proc. on “Variational Methods" (H. Berestycki- J.M. Coron- I. Ekeland, Ed.) Paris (1988) 413-429.
4. On the existence of multiple geodesics in static space-times;Benci, V.;Ann. Inst. H. Poincar\'{e} Anal. Non Lin\'{e}aire,1991
5. [5] V. Benci, D. Fortunato, F. Giannoni: On the existence of periodic trajectories in static Lorentzian manifolds with singular boundary, Nonlinear Analysis, a tribute in honour of Giovanni Prodi, Pisa (1991) 109-133.