@article{DE_1980_16_8_a13,
     author = {V. O. Mishchenko},
     title = {Expansion in eigenfunctions of a symmetric abstract elliptic differential operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1474--1483},
     publisher = {mathdoc},
     volume = {16},
     number = {8},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_8_a13/}
}