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@article{MZ_1991__206_1_174233, author = {Hidekazu Ito}, title = {Action-angle coordinates at singularities for analytic integrable systems.}, journal = {Mathematische Zeitschrift}, pages = {363--408}, publisher = {mathdoc}, volume = {206}, number = {1}, year = {1991}, zbl = {0707.58026}, url = {http://geodesic.mathdoc.fr/item/MZ_1991__206_1_174233/} }
Hidekazu Ito. Action-angle coordinates at singularities for analytic integrable systems.. Mathematische Zeitschrift, Tome 206 (1991) no. 1, pp. 363-408. http://geodesic.mathdoc.fr/item/MZ_1991__206_1_174233/