@article{DE_1988_24_12_a1,
     author = {V. K. Akhramenko and A. P. Sadovskii},
     title = {Necessary conditions for a center for a differential system with a complex singular point},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2032--2042},
     publisher = {mathdoc},
     volume = {24},
     number = {12},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_12_a1/}
}