@article{DE_1967_3_4_a5,
     author = {O. A. Liskovets},
     title = {Incorrect problems with a closed non-invertible operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {636--646},
     publisher = {mathdoc},
     volume = {3},
     number = {4},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1967_3_4_a5/}
}