@article{DAN_1957_114_2_a7,
     author = {G. I. Natanson},
     title = {On the theory of approximation of functions by linear combinations of {Sturm--Liouville} characteristic functions},
     journal = {Doklady Akademii Nauk},
     pages = {263--266},
     publisher = {mathdoc},
     volume = {114},
     number = {2},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_114_2_a7/}
}