@article{DAN_1976_227_4_a5,
     author = {V. A. Il'in},
     title = {Necessary and sufficient conditions for a subsystem of the eigen- and associated functions of a {Keldys} bundle of ordinary differential operators to be a basis},
     journal = {Doklady Akademii Nauk},
     pages = {796--799},
     publisher = {mathdoc},
     volume = {227},
     number = {4},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1976_227_4_a5/}
}