@article{DE_1990_26_11_a8,
     author = {N. A. Izobov and O. P. Stepanovich},
     title = {Properties of the coefficient of nonregularity of linear systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1899--1906},
     publisher = {mathdoc},
     volume = {26},
     number = {11},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_11_a8/}
}