@article{DE_1968_4_12_a6,
     author = {Yu. S. Shatalov},
     title = {A certain method of investigating singular problems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2215--2229},
     publisher = {mathdoc},
     volume = {4},
     number = {12},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_12_a6/}
}