@article{ZVMMF_1994_34_3_a14,
     author = {V. L. Kalitvyanskiǐ},
     title = {Perturbation theory for the {Sturm{\textendash}Liouville} problem with variable coefficients},
     journal = {\v{Z}urnal vy\v{c}islitelʹnoj matematiki i matemati\v{c}eskoj fiziki},
     pages = {491--494},
     publisher = {mathdoc},
     volume = {34},
     number = {3},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZVMMF_1994_34_3_a14/}
}