@article{RM_1973_28_2_a12,
     author = {V. P. Belogrud' and A. G. Kostyuchenko},
     title = {The density of the spectrum of a {Sturm{\textendash}Liouville} operator},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     year = {1973},
     volume = {28},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1973_28_2_a12/}
}