@article{DAN_1962_142_3_a9,
     author = {A. S. Markus},
     title = {The root-vector expansion of a weakly perturbed self-adjoint operator},
     journal = {Doklady Akademii Nauk},
     pages = {538--541},
     publisher = {mathdoc},
     volume = {142},
     number = {3},
     year = {1962},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1962_142_3_a9/}
}