@article{DAN_1968_183_4_a14,
     author = {R. A. Shirikyan},
     title = {The spectrum of nonselfadjoint differential operators},
     journal = {Doklady Akademii Nauk},
     pages = {791--792},
     year = {1968},
     volume = {183},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_183_4_a14/}
}