@article{DE_1997_33_6_a16,
     author = {S. R. Umarov},
     title = {Nonlocal boundary value problems for pseudodifferential and operator-differential {equations.~I}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {827--836},
     publisher = {mathdoc},
     volume = {33},
     number = {6},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1997_33_6_a16/}
}