@article{DAN_1987_295_4_a0,
     author = {A. A. Agrachev and A. V. Sarychev},
     title = {Filtrations of a {Lie} algebra of vector fields and the nilpotent},
     journal = {Doklady Akademii Nauk},
     pages = {777--781},
     publisher = {mathdoc},
     volume = {295},
     number = {4},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1987_295_4_a0/}
}