@article{DE_1997_33_5_a18,
     author = {L. A. Cherkas},
     title = {The {Dulac} function for polynomial autonomous systems on a plane},
     journal = {Differencialʹnye uravneni\^a},
     pages = {689--699},
     publisher = {mathdoc},
     volume = {33},
     number = {5},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1997_33_5_a18/}
}