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@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}, publisher = {mathdoc}, volume = {64}, number = {1}, year = {1989}, zbl = {0686.58021}, url = {http://geodesic.mathdoc.fr/item/CMH_1989__64_1_140164/} }
Hidekazu Ito. Convergence of Birkhoff normal forms for integrable systems.. Commentarii mathematici Helvetici, Tome 64 (1989) no. 1, pp. 412-461. http://geodesic.mathdoc.fr/item/CMH_1989__64_1_140164/