@article{DE_1987_23_9_a22,
     author = {L. A. Lepin},
     title = {The method of lower and upper functions for second-order differential equations with singularities},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1632--1634},
     publisher = {mathdoc},
     volume = {23},
     number = {9},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_9_a22/}
}