@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/}
}