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@article{DE_1968_4_11_a0, author = {K. S. Sibirskii}, title = {On some questions of the existence of the center}, journal = {Differencialʹnye uravneni\^a}, pages = {1931--1938}, publisher = {mathdoc}, volume = {4}, number = {11}, year = {1968}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1968_4_11_a0/} }
K. S. Sibirskii. On some questions of the existence of the center. Differencialʹnye uravneniâ, Tome 4 (1968) no. 11, pp. 1931-1938. http://geodesic.mathdoc.fr/item/DE_1968_4_11_a0/