@article{DE_1985_21_5_a25,
     author = {A. V. Lasunsky},
     title = {On a small variation of the characteristic indices of a regular linear system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {901--903},
     publisher = {mathdoc},
     volume = {21},
     number = {5},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_5_a25/}
}