@article{MMO_1956_5_a4,
     author = {B. M. Levitan},
     title = {On the expansion according to the eigenfunctions of a self-adjoint partial differential equation},
     journal = {Trudy Moskovskogo matemati\v{c}eskogo ob\^{s}estva},
     pages = {269--298},
     publisher = {mathdoc},
     volume = {5},
     year = {1956},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MMO_1956_5_a4/}
}