@article{DE_1991_27_12_a3,
     author = {I. A. Volkov},
     title = {Boundaries of a set of characteristic exponents of linear differential systems with higher-order perturbations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2050--2053},
     publisher = {mathdoc},
     volume = {27},
     number = {12},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1991_27_12_a3/}
}