@article{DAN_1966_168_1_a3,
     author = {A. G. Kostyuchenko},
     title = {Distribution of eigenvalues of singular differential operators},
     journal = {Doklady Akademii Nauk},
     pages = {21--24},
     publisher = {mathdoc},
     volume = {168},
     number = {1},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1966_168_1_a3/}
}