1. Multiple homoclinic orbits for a class of conservative systems;Ambrosetti;Rend. Sem. Mat. Univ. Padova,1993
2. Second order nonautonomous systems with symmetric potential changing sign;Antonacci;Rend. Mat. Appl. (7),1998
3. Existence of homoclinic solutions for a class of time-dependent Hamiltonian systems;Carrião;J. Math. Anal. Appl.,1999
4. Homoclinic orbits for second order Hamiltonian systems possessing superquadratic potentials;Coti Zelati;J. Amer. Math. Soc.,1991
5. Direct Methods in the Calculus of Variations;Dacorogna,1989