@article{KUIPM_1989_a13,
     author = {A. M. Sidorov},
     title = {Eigenvalues and eigenvectors of a perturbed operator},
     journal = {Issledovaniya po Prikladnoi Matematike i Informatike},
     pages = {131--138},
     publisher = {mathdoc},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/KUIPM_1989_a13/}
}