@article{IM2_1987_28_2_a7,
     author = {S. Ya. Yakubov},
     title = {Multiple completeness in the sense of {M.\,V.~Keldysh} of root functions of elliptic boundary value problems with a~polynomial spectral parameter},
     journal = {Izvestiya. Mathematics },
     pages = {413--420},
     publisher = {mathdoc},
     volume = {28},
     number = {2},
     year = {1987},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1987_28_2_a7/}
}