@article{DE_1984_20_2_a0,
     author = {A. F. Andreev and P. D. Khody-Zade},
     title = {Investigation of the problem of the center and focus in one case},
     journal = {Differencialʹnye uravneni\^a},
     pages = {187--197},
     publisher = {mathdoc},
     volume = {20},
     number = {2},
     year = {1984},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1984_20_2_a0/}
}