@article{DE_1965_1_4_a6,
     author = {N. A. Izobov},
     title = {On a set of lower indices of a linear differential system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {469--477},
     publisher = {mathdoc},
     volume = {1},
     number = {4},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1965_1_4_a6/}
}