@article{DE_1991_27_1_a18,
     author = {B. T. Bilalov},
     title = {Necessary and sufficient condition for the completeness of a system of functions},
     journal = {Differencialʹnye uravneni\^a},
     pages = {158--161},
     publisher = {mathdoc},
     volume = {27},
     number = {1},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1991_27_1_a18/}
}