@article{DA_1980_20_a6,
     author = {T. S. Trofimchuk},
     title = {Controllability of systems that are not solvable with respect to the highest derivative},
     journal = {Diskretnyj analiz i issledovanie operacij},
     pages = {74--82},
     publisher = {mathdoc},
     number = {20},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DA_1980_20_a6/}
}