@article{AIHPA_1988__48_4_423_0,
     author = {Giorgilli, Antonio},
     title = {Rigorous results on the power expansions for the integrals of a hamiltonian system near an elliptic equilibrium point},
     journal = {Annales de l'I.H.P. Physique th\'eorique},
     pages = {423--439},
     publisher = {Gauthier-Villars},
     volume = {48},
     number = {4},
     year = {1988},
     mrnumber = {969174},
     zbl = {0669.34002},
     language = {en},
     url = {http://www.numdam.org/item/AIHPA_1988__48_4_423_0/}
}