@article{DE_1987_23_5_a7,
     author = {A. A. Levakov},
     title = {On the controllability of linear nonstationary systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {798--806},
     publisher = {mathdoc},
     volume = {23},
     number = {5},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_5_a7/}
}