@article{DE_1970_6_7_a2,
     author = {L. A. Cherkas and L. I. Zhilevich},
     title = {Some tests for the absence or uniqueness of limit cycles},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1170--1178},
     publisher = {mathdoc},
     volume = {6},
     number = {7},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_7_a2/}
}