Bad normed spaces, convexity properties, separated sets

Some years ago, a parameter–denoted by A 1 ( X ) –was defined in real Banach spaces. In the same setting, several years before, a notion called Q - convexity had been defined. Studying these two notions seems to be rather awkward and up until now this has not been done in deep. Here we indicate some...

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Veröffentlicht in:Nonlinear analysis 2010-09, Vol.73 (6), p.1491-1494
1. Verfasser: Papini, Pier Luigi
Format: Artikel
Sprache:eng
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Zusammenfassung:Some years ago, a parameter–denoted by A 1 ( X ) –was defined in real Banach spaces. In the same setting, several years before, a notion called Q - convexity had been defined. Studying these two notions seems to be rather awkward and up until now this has not been done in deep. Here we indicate some properties and connections between these two parameters and some other related ones, in infinite-dimensional Banach spaces. We also consider another notion, a natural extension of Q -convexity, and we discuss the case when A 1 ( X ) attains its maximum value. The spaces where this happens can be considered as ”bad” since they cannot have several properties which are usually considered as nice (like uniform non-squareness or P -convexity).
ISSN:0362-546X
1873-5215
DOI:10.1016/j.na.2010.04.030