@article{DE_1980_16_3_a14,
     author = {\`E. M. Saak},
     title = {Fredholm property of a class of boundary value problems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {507--515},
     publisher = {mathdoc},
     volume = {16},
     number = {3},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_3_a14/}
}