1. A variational approach to homoclinic orbits in Hamiltonian systems;Zelati,1988
2. W. Klingenberg, “Lectures on Closed Geodesics,” Springer-Verlag, New York/Berlin.
3. Periodic and heteroclinic orbits for a periodic Hamiltonian systems;Rabiniwitz,1988
4. Nonlinear Functional Analysis;Schwartz,1969
5. Homoclinic orbits for a singular second order Hamiltonian system;Tanaka,1989