@article{DE_1990_26_1_a3,
     author = {A. A. Dezin},
     title = {Perturbations of the point spectrum},
     journal = {Differencialʹnye uravneni\^a},
     pages = {23--30},
     publisher = {mathdoc},
     volume = {26},
     number = {1},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_1_a3/}
}