@article{DAN_1966_167_3_a7,
     author = {V. A. Trenogin},
     title = {Perturbation of the eigenvalues and eigenelements of linear operators},
     journal = {Doklady Akademii Nauk},
     pages = {519--522},
     year = {1966},
     volume = {167},
     number = {3},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1966_167_3_a7/}
}