@article{DE_1981_17_10_a19,
     author = {V. A. Sadovnichii and V. A. Lyubishkin},
     title = {Some questions of the theory of perturbations of linear operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1911--1914},
     publisher = {mathdoc},
     volume = {17},
     number = {10},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1981_17_10_a19/}
}