1. Periodic Solutions of Singular Lagrangian Systems;Ambrosetti,1993
2. Periodic and homoclinic solutions to a class of Hamiltonian systems with indefinite potential in sign;Antonacci;Boll. Unione Mat. Ital.,1996
3. Existence of periodic solutions of Hamiltonian systems with potential indefinite in sign;Antonacci;Nonlinear Anal.,1997
4. Second order nonautonomous systems with symmetric potential changing sign;Antonacci;Rend. Mat. Appl.,1998
5. Existence of three periodic solutions for a non-autonomous second order system;Barletta;Matematiche (Catania),2002