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@article{DE_1977_13_2_a4, author = {L. A. Cherkas}, title = {Conditions for the center for a certain equation}, journal = {Differencialʹnye uravneni\^a}, pages = {271--275}, publisher = {mathdoc}, volume = {13}, number = {2}, year = {1977}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1977_13_2_a4/} }
L. A. Cherkas. Conditions for the center for a certain equation. Differencialʹnye uravneniâ, Tome 13 (1977) no. 2, pp. 271-275. http://geodesic.mathdoc.fr/item/DE_1977_13_2_a4/