@article{DE_1971_7_1_a14,
     author = {M. V. Fokin},
     title = {The spectrum of a certain operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {135--141},
     publisher = {mathdoc},
     volume = {7},
     number = {1},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1971_7_1_a14/}
}