@article{DE_1988_24_6_a9,
     author = {Yu. V. Churin},
     title = {Closure of a set of systems with singular periodic solutions},
     journal = {Differencialʹnye uravneni\^a},
     pages = {999--1004},
     publisher = {mathdoc},
     volume = {24},
     number = {6},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1988_24_6_a9/}
}