@article{DAN_1975_222_5_a1,
     author = {I. I. Ibragimov and I. F. Kushnirchuk},
     title = {On the completeness of the system of eigenfunctions of a class of partial differential operators},
     journal = {Doklady Akademii Nauk},
     pages = {1020--1023},
     publisher = {mathdoc},
     volume = {222},
     number = {5},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1975_222_5_a1/}
}