@article{DE_1967_3_6_a2,
     author = {M. V. Dolov},
     title = {Differential equations $yy'=Q_4(x,y)$, having an ellipse as limit cycle},
     journal = {Differencialʹnye uravneni\^a},
     pages = {898--904},
     publisher = {mathdoc},
     volume = {3},
     number = {6},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1967_3_6_a2/}
}