@article{DE_1981_17_6_a19,
     author = {V. I. Filippenko},
     title = {On the multiplicity of a spectrum of a first-order selfadjoint differential operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1135--1138},
     publisher = {mathdoc},
     volume = {17},
     number = {6},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1981_17_6_a19/}
}