@article{DE_1986_22_6_a4,
     author = {K. S. Sibirskii},
     title = {Centroaffine invariant center conditions in the sense of {Dulac} for a quadratic differential system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {954--961},
     publisher = {mathdoc},
     volume = {22},
     number = {6},
     year = {1986},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1986_22_6_a4/}
}