@article{DAN_1969_188_3_a0,
     author = {O. A. Akperova and M. G. Dzhavadov},
     title = {Expansion in the eigenfunctions which correspond to a certain part of the set of eigenvalues of a second order nonselfadjoint differential operator},
     journal = {Doklady Akademii Nauk},
     pages = {503--506},
     publisher = {mathdoc},
     volume = {188},
     number = {3},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_188_3_a0/}
}