@article{DE_2000_36_8_a0,
     author = {O. V. Belyantsev},
     title = {The {Bessel} inequality and the basis property of root functions of a second-order singular differential operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1011--1020},
     year = {2000},
     volume = {36},
     number = {8},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2000_36_8_a0/}
}