@article{RM_1960_15_1_a7,
     author = {Yu. S. Bogdanov},
     title = {On the existence of an approximative sequence for a~regular linear differential system},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     year = {1960},
     volume = {15},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1960_15_1_a7/}
}