@article{MZM_1976_20_6_a7,
     author = {M. Otelbaev},
     title = {Bounds for eigenvalues of singular differential operators},
     journal = {Matemati\v{c}eskie zametki},
     pages = {859--867},
     publisher = {mathdoc},
     volume = {20},
     number = {6},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1976_20_6_a7/}
}