@article{MZM_1969_6_6_a9,
     author = {A. M. Olevskii},
     title = {On the extension of a~sequence of functions to a~complete orthonormal system},
     journal = {Matemati\v{c}eskie zametki},
     pages = {737--747},
     year = {1969},
     volume = {6},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1969_6_6_a9/}
}