@article{DAN_1964_158_3_a1,
     author = {M. A. Gol'dman and S. N. Krachkovskii},
     title = {On certain perturbations of a closed linear operator},
     journal = {Doklady Akademii Nauk},
     pages = {507--509},
     publisher = {mathdoc},
     volume = {158},
     number = {3},
     year = {1964},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1964_158_3_a1/}
}