@article{DE_1972_8_12_a12,
     author = {K. S. Sibirskii},
     title = {The problem of an algebraic integral in the case of the center},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2211--2214},
     publisher = {mathdoc},
     volume = {8},
     number = {12},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_12_a12/}
}