@article{DE_1995_31_1_a28,
     author = {D. S. Ushkho},
     title = {On the coexistence of limit cycles and singular points of {\textquotedblleft}center{\textquotedblright} type of cubic differential systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {173--174},
     year = {1995},
     volume = {31},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1995_31_1_a28/}
}