1. Semi-Riemannian Geometry with Applications to Relativity;O’Neill,1983
2. On the existence of multiple geodesics in static space-times;Benci;Ann. Inst. Henri Poincaré,1991
3. Infinitely many spacelike periodic trajectories on a class of Lorentz manifolds;Greco;Rend. Sem. Mat. Padova,1994
4. Periodic solutions of asymptotically linear dynamical systems;Benci;Nonlinear Differential Equations and Applications,1994
5. V. Benci D. Fortunato, Estimate of the number of periodic solutions via the twist number, to appear.