@article{DE_1995_31_6_a22,
     author = {V. G. Romanovsky},
     title = {Center conditions for a cubic system with four complex parameters},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1091--1093},
     publisher = {mathdoc},
     volume = {31},
     number = {6},
     year = {1995},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1995_31_6_a22/}
}