@article{DAN_1957_112_6_a3,
     author = {V. B. Lidskii},
     title = {A theorem on the spectra of a perturbed differential operator},
     journal = {Doklady Akademii Nauk},
     pages = {994--997},
     publisher = {mathdoc},
     volume = {112},
     number = {6},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_112_6_a3/}
}