@article{DE_1966_2_3_a4,
     author = {A. I. Yablonskii},
     title = {On limit cycles of a certain differential equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {335--344},
     publisher = {mathdoc},
     volume = {2},
     number = {3},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1966_2_3_a4/}
}