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@article{DAN_1961_137_5_a14, author = {V. A. Pliss}, title = {The existence of periodic solutions of certain non-linear systems}, journal = {Doklady Akademii Nauk}, pages = {1060--1062}, publisher = {mathdoc}, volume = {137}, number = {5}, year = {1961}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DAN_1961_137_5_a14/} }
V. A. Pliss. The existence of periodic solutions of certain non-linear systems. Doklady Akademii Nauk, Tome 137 (1961) no. 5, pp. 1060-1062. http://geodesic.mathdoc.fr/item/DAN_1961_137_5_a14/