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@article{DE_1972_8_10_a17, author = {N. G. Bulgakov}, title = {On the existence of periodic solutions to nonlinear systems}, journal = {Differencialʹnye uravneni\^a}, pages = {1876--1877}, publisher = {mathdoc}, volume = {8}, number = {10}, year = {1972}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1972_8_10_a17/} }
N. G. Bulgakov. On the existence of periodic solutions to nonlinear systems. Differencialʹnye uravneniâ, Tome 8 (1972) no. 10, pp. 1876-1877. http://geodesic.mathdoc.fr/item/DE_1972_8_10_a17/