@article{DE_1969_5_4_a0,
     author = {V. P. Glushko},
     title = {Degenerate linear differential equations. {IV}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {599--611},
     publisher = {mathdoc},
     volume = {5},
     number = {4},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_4_a0/}
}