@article{DE_1989_25_4_a19,
     author = {E. P. Bogomolova},
     title = {Necessary conditions for the basis property in the direct sum of {Sobolev} spaces},
     journal = {Differencialʹnye uravneni\^a},
     pages = {722--723},
     publisher = {mathdoc},
     volume = {25},
     number = {4},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1989_25_4_a19/}
}