@article{DE_1968_4_5_a4,
     author = {M. V. Dolov},
     title = {A certain method of investigation of limit cycles},
     journal = {Differencialʹnye uravneni\^a},
     pages = {812--820},
     publisher = {mathdoc},
     volume = {4},
     number = {5},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_5_a4/}
}