@article{AIHPC_1997__14_6_691_0,
     author = {Bartsch, Thomas},
     title = {A generalization of the {Weinstein-Moser} theorems on periodic orbits of a hamiltonian system near an equilibrium},
     journal = {Annales de l'I.H.P. Analyse non lin\'eaire},
     pages = {691--718},
     publisher = {Gauthier-Villars},
     volume = {14},
     number = {6},
     year = {1997},
     mrnumber = {1482899},
     zbl = {0891.58034},
     language = {en},
     url = {http://archive.numdam.org/item/AIHPC_1997__14_6_691_0/}
}