@article{DE_1967_3_12_a5,
     author = {\`E. V. Vdovina},
     title = {Some theorems on limit cycles},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2053--2057},
     publisher = {mathdoc},
     volume = {3},
     number = {12},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1967_3_12_a5/}
}