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Auerbach Bases and Minimal Volume Sufficient Enlargements

Published online by Cambridge University Press:  20 November 2018

M. I. Ostrovskii*
Affiliation:
Department of Mathematics and Computer Science, St. John's University, Queens, NY 11439, U.S.A.e-mail: ostrovsm@stjohns.edu
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Abstract

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Let ${{B}_{Y}}$ denote the unit ball of a normed linear space $Y$. A symmetric, bounded, closed, convex set $A$ in a finite dimensional normed linear space $X$ is called a sufficient enlargement for $X$ if, for an arbitrary isometric embedding of $X$ into a Banach space $Y$, there exists a linear projection $P:\,Y\,\to \,X$ such that $P({{B}_{Y}})\,\subset \,A$. Each finite dimensional normed space has a minimal-volume sufficient enlargement that is a parallelepiped; some spaces have “exotic” minimal-volume sufficient enlargements. The main result of the paper is a characterization of spaces having “exotic” minimal-volume sufficient enlargements in terms of Auerbach bases.

Keywords

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 2011

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