Abstract
We prove that, if the centralizer of a Banach space X is infinite-dimensional, then every nonempty relatively weakly open subset of the closed unit ball of X has diameter equal to 2. This result, together with a suitable refinement also proven in the paper, contains (and improves in some cases) previously known facts for C *-algebras, JB *-triples, spaces of vector valued continuous functions, and spaces of operators.
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Partially supported by Junta de Andalucía grants FQM 0199 and FQM 1215, and Project I+D MCYT MTM-2004-03882 and MTM-2006-15546-C02-02.
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Becerra Guerrero, J., Rodríguez-Palacios, A. Relatively weakly open sets in closed balls of Banach spaces, and the centralizer. Math. Z. 262, 557–570 (2009). https://doi.org/10.1007/s00209-008-0389-3
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DOI: https://doi.org/10.1007/s00209-008-0389-3