@article{DE_1982_18_1_a3,
     author = {V. A. Il'in},
     title = {Relations that are exact with respect to order between $L_2$-norms of eigen- and associated functions of a second-order elliptic operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {30--37},
     publisher = {mathdoc},
     volume = {18},
     number = {1},
     year = {1982},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1982_18_1_a3/}
}