@article{ASNSP_1994_4_21_4_541_0,
     author = {Chierchia, L. and Falcolini, C.},
     title = {A direct proof of a theorem by {Kolmogorov} in hamiltonian systems},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {541--593},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 21},
     number = {4},
     year = {1994},
     zbl = {0836.34040},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1994_4_21_4_541_0/}
}