Multiple Solutions for Indefinite Functionals and Applications to Asymptotically Linear Problems

In this paper, by means of Morse theory of isolated critical points (orbits) we study further the critical points theory of asymptotically quadratic functionals and give some results concerning the exis- fence of multiple critical points forbits) which generalize a series of previous results due to Amann. Conley. Zehnder and K.C. Chang. As applications. the existence of multiple periodic solutions for asymptotically linear Hamiltonian systems is investigated. And our results generalize some recent ones due to Coti- Zelati.J.Q. Liu.S.Li, etc.