@article{DE_1991_27_5_a5,
     author = {A. A. Liverovskiy and N. N. Petrov},
     title = {Some differential-topological problems in control theory},
     journal = {Differencialʹnye uravneni\^a},
     pages = {771--777},
     year = {1991},
     volume = {27},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1991_27_5_a5/}
}