An extension of the normed dual functors

Abstract

By means of the direct limit technique, with every normed space X it is associated a bidualic (Banach) space $\tilde{X} (D^2( \tilde{X}) \cong \tilde{X} $ - called the hyperdual of $X$) that contains (isometrically embedded) $X$ as well as all the even (normed) duals $D^{2n}(X)$, which make an increasing sequence of the category retracts. The algebraic dimension dim $\tilde{X}$ = dim $X$ (dim $\tilde{X}$ = $2^{\aleph_0}$ ), whenever dim $X \neq \aleph_0$, (dim $X = \aleph_0$). Furthermore, the correspondence $X \mapsto \tilde{X}$ extends to a faithful covariant functor (called the hyperdual functor) on the category of normed spaces.