@article{DE_1972_8_10_a1,
     author = {E. A. Begovatov},
     title = {A condition for the completeness of the system of root subspaces of a {Sturm--Liouville} type operator in {Hilbert} space},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1738--1744},
     publisher = {mathdoc},
     volume = {8},
     number = {10},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_10_a1/}
}