@article{DE_1998_34_10_a7,
     author = {L. A. Cherkas and A. A. Grin'},
     title = {A {Dulac} function in a half-plane in the form of a polynomial of the second degree for a quadratic system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1346--1348},
     publisher = {mathdoc},
     volume = {34},
     number = {10},
     year = {1998},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1998_34_10_a7/}
}