@article{DE_1993_29_9_a1,
     author = {M. V. Dolov and R. V. Kuz'min},
     title = {On the limit cycles of a class of systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1481--1485},
     publisher = {mathdoc},
     volume = {29},
     number = {9},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1993_29_9_a1/}
}