@article{DAN_1988_299_4_a8,
     author = {N. B. Kerimov},
     title = {Necessary conditions for the property of being a basis in $L_2(G)$ for a system of eigen- and associated functions of a second-order},
     journal = {Doklady Akademii Nauk},
     pages = {809--811},
     publisher = {mathdoc},
     volume = {299},
     number = {4},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1988_299_4_a8/}
}