@article{DE_1990_26_3_a28,
     author = {Yu. V. Malyshev and V. P. Zakharov},
     title = {Integrating factors and limit cycles},
     journal = {Differencialʹnye uravneni\^a},
     pages = {542--544},
     publisher = {mathdoc},
     volume = {26},
     number = {3},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_3_a28/}
}