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@article{DE_1970_6_10_a20, author = {N. N. Vinogradov}, title = {The existence of a periodic solution of a nonlinear system of three differential equations}, journal = {Differencialʹnye uravneni\^a}, pages = {1901}, publisher = {mathdoc}, volume = {6}, number = {10}, year = {1970}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1970_6_10_a20/} }
N. N. Vinogradov. The existence of a periodic solution of a nonlinear system of three differential equations. Differencialʹnye uravneniâ, Tome 6 (1970) no. 10. http://geodesic.mathdoc.fr/item/DE_1970_6_10_a20/