@article{MZM_1968_3_4_a5,
     author = {M. M. Gekhtman},
     title = {Localization of the spectrum of certain non-self-adjoint operators},
     journal = {Matemati\v{c}eskie zametki},
     pages = {415--419},
     publisher = {mathdoc},
     volume = {3},
     number = {4},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1968_3_4_a5/}
}