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@article{CMUC_1984__25_2_a15, author = {Dane\v{s}, Josef}, title = {On the radius of a set in a {Hilbert} space}, journal = {Commentationes Mathematicae Universitatis Carolinae}, pages = {355--362}, publisher = {mathdoc}, volume = {25}, number = {2}, year = {1984}, mrnumber = {768823}, zbl = {0568.46018}, language = {en}, url = {http://geodesic.mathdoc.fr/item/CMUC_1984__25_2_a15/} }
Daneš, Josef. On the radius of a set in a Hilbert space. Commentationes Mathematicae Universitatis Carolinae, Tome 25 (1984) no. 2, pp. 355-362. http://geodesic.mathdoc.fr/item/CMUC_1984__25_2_a15/