@article{DE_1968_4_6_a5,
     author = {L. A. Cherkas},
     title = {The stability of singular cycles},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1012--1017},
     publisher = {mathdoc},
     volume = {4},
     number = {6},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_6_a5/}
}