A Characterization of Extremal Sets in Hilbert Spaces
arXiv:math/0203190
Abstract
We give a characterization of extremal sets in Hilbert spaces that generalizes a classical theorem of H. W. E. Jung. We investigate also the behaviour of points near to the circumsphere of such a set with respect to the Kuratowski and Hausdorff measures of non-compactness.
10 pages, corrected some misprints