@article{CMH_1989__64_1_140164,
     author = {Hidekazu Ito},
     title = {Convergence of {Birkhoff} normal forms for integrable systems.},
     journal = {Commentarii mathematici Helvetici},
     pages = {412--461},
     year = {1989},
     volume = {64},
     number = {1},
     zbl = {0686.58021},
     url = {http://geodesic.mathdoc.fr/item/CMH_1989__64_1_140164/}
}