@article{DAN_1957_115_4_a1,
     author = {V. N. Gol'dberg},
     title = {Perturbation of linear operators with a purely discrete spectrum},
     journal = {Doklady Akademii Nauk},
     pages = {643--645},
     publisher = {mathdoc},
     volume = {115},
     number = {4},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_115_4_a1/}
}