@article{DAN_1988_301_6_a2,
     author = {N. I. Vulpe and K. S. Sibirskii},
     title = {Centro-affine invariant conditions for the existence of a center},
     journal = {Doklady Akademii Nauk},
     pages = {1297--1301},
     publisher = {mathdoc},
     volume = {301},
     number = {6},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1988_301_6_a2/}
}