@article{DE_1984_20_5_a5,
     author = {A. G. Surkov},
     title = {Sharp bounds for characteristic indices of second-order linear systems with bounded perturbations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {792--797},
     publisher = {mathdoc},
     volume = {20},
     number = {5},
     year = {1984},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1984_20_5_a5/}
}