@article{DE_1983_19_9_a8,
     author = {A. G. Surkov},
     title = {Sharp upper and lower bounds for characteristic indices of a two-dimensional system with bounded perturbations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1534--1541},
     publisher = {mathdoc},
     volume = {19},
     number = {9},
     year = {1983},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1983_19_9_a8/}
}