@article{DE_1987_23_9_a8,
     author = {L. A. Cherkas and V. A. Gaǐko},
     title = {Bifurcations of limit cycles of a quadratic system with two singular points and two parameters that rotate the field},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1544--1553},
     publisher = {mathdoc},
     volume = {23},
     number = {9},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_9_a8/}
}