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@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/} }
Yu. V. Churin. Closure of a set of systems with singular periodic solutions. Differencialʹnye uravneniâ, Tome 24 (1988) no. 6, pp. 999-1004. http://geodesic.mathdoc.fr/item/DE_1988_24_6_a9/