@article{DE_1968_4_4_a7,
     author = {V. P. Skripnik},
     title = {Degenerate systems and a small parameter at the derivative},
     journal = {Differencialʹnye uravneni\^a},
     pages = {646--658},
     publisher = {mathdoc},
     volume = {4},
     number = {4},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_4_a7/}
}