@article{SM_1984_48_2_a11,
     author = {Kh. Zholondek},
     title = {On the versality of a~family of symmetric vector fields in the plane},
     journal = {Sbornik. Mathematics},
     pages = {463--492},
     year = {1984},
     volume = {48},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1984_48_2_a11/}
}