@article{DE_1988_24_5_a14,
     author = {V. A. Il'in},
     title = {An estimate for the difference of the {Riesz} means of two spectral expansions for a function in the class~$L_2$},
     journal = {Differencialʹnye uravneni\^a},
     pages = {852--863},
     publisher = {mathdoc},
     volume = {24},
     number = {5},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_5_a14/}
}