@article{DE_1990_26_11_a16,
     author = {V. S. Il'kiv},
     title = {Perturbations of a nonlocal problem for differential equations with pseudodifferential coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1962--1971},
     publisher = {mathdoc},
     volume = {26},
     number = {11},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_11_a16/}
}