@article{DE_1973_9_3_a6,
     author = {A. K. Ratyni},
     title = {Differential inequalities for the {Sturm--Liouville} problem},
     journal = {Differencialʹnye uravneni\^a},
     pages = {456--464},
     publisher = {mathdoc},
     volume = {9},
     number = {3},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1973_9_3_a6/}
}