@article{DAN_1989_309_1_a2,
     author = {A. I. Vagabov},
     title = {Summation of $n$-multiple expansions in principal functions of
},
     journal = {Doklady Akademii Nauk},
     pages = {20--23},
     publisher = {mathdoc},
     volume = {309},
     number = {1},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_309_1_a2/}
}