Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
11012930 | Journal of Functional Analysis | 2018 | 21 Pages |
Abstract
We prove the symmetric version of Kottman's theorem, that is to say, we demonstrate that the unit sphere of an infinite-dimensional Banach space contains an infinite subset A with the property that âx±yâ>1 for distinct elements x,yâA, thereby answering a question of J.M.F. Castillo. In the case where X contains an infinite-dimensional separable dual space or an unconditional basic sequence, the set A may be chosen in a way that âx±yâ⩾1+ε for some ε>0 and distinct x,yâA. Under additional structural properties of X, such as non-trivial cotype, we obtain quantitative estimates for the said ε. Certain renorming results are also presented.
Related Topics
Physical Sciences and Engineering
Mathematics
Algebra and Number Theory
Authors
Petr Hájek, Tomasz Kania, Tommaso Russo,