@article{DE_1966_2_9_a1,
     author = {G. I. Laptev},
     title = {Eigenvalue problems for differential equations of the second order in {Banach} and {Hilbert} spaces},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1151--1160},
     publisher = {mathdoc},
     volume = {2},
     number = {9},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1966_2_9_a1/}
}