“…Background information and applications of Hamiltonian systems can be found for example in [16,28,31,37]. The monographs [29,32] have inspired a great deal of work on the existence and multiplicity of periodic solutions for Hamiltonian systems using variational techniques; for example, see [9,10,11,13,14,15,18,19,24,25,26,36,38,40,42,43,45] and the references therein.…”