@article{DAN_1973_208_6_a7,
     author = {P. V. Popov},
     title = {Variational principles for the spectrum of nonselfadjoint operators},
     journal = {Doklady Akademii Nauk},
     pages = {1290--1292},
     publisher = {mathdoc},
     volume = {208},
     number = {6},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1973_208_6_a7/}
}