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@article{DE_1972_8_12_a22, author = {G. S. Rychkov}, title = {The limit cycles of the equation $u(x+1)du=(-x+ax^2+bxu+cu+du^2)dx$}, journal = {Differencialʹnye uravneni\^a}, pages = {2257--2259}, publisher = {mathdoc}, volume = {8}, number = {12}, year = {1972}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1972_8_12_a22/} }
G. S. Rychkov. The limit cycles of the equation $u(x+1)du=(-x+ax^2+bxu+cu+du^2)dx$. Differencialʹnye uravneniâ, Tome 8 (1972) no. 12, pp. 2257-2259. http://geodesic.mathdoc.fr/item/DE_1972_8_12_a22/