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@article{DE_1981_17_9_a26, author = {L. A. Cherkas}, title = {Two remarks with respect to conditions for a center}, journal = {Differencialʹnye uravneni\^a}, pages = {1709--1712}, publisher = {mathdoc}, volume = {17}, number = {9}, year = {1981}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1981_17_9_a26/} }
L. A. Cherkas. Two remarks with respect to conditions for a center. Differencialʹnye uravneniâ, Tome 17 (1981) no. 9, pp. 1709-1712. http://geodesic.mathdoc.fr/item/DE_1981_17_9_a26/