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Norm Hilbert Spaces

Norm Hilbert spaces
Authors: Ochsenius, H.; Schikhof, W.H.;

Norm Hilbert Spaces

Abstract

Let \(K\) be a field complete with respect to some valuation 1.1 and let \(E=(E,\|\cdot \|)\) be a \(K\)-Banach space. \(K\)-Banach spaces \(E\) such that for each closed subspace \(D\) there exists a linear surjective projection \(P:E\to D\) satisfying \(\| Px\|\leq\| x\|\) for all \(x\in E\) are called norm Hilbert spaces (NHS). The authors introduce and characterize NHS in this paper. They also describe those NHS for which there exists a Hermitian form \((\cdot,\cdot)\) satisfying \(|(x,x)|= \| x\|^2\) for all \(x\). The main results proved are: Theorem 4.2: A norm Hilbert space is of countable type (and has an orthogonal base). Theorem 4.3: Let \(E\) be an infinite-dimensional \(K\)-Banach space with orthogonal base \(e_1,e_2,\dots\), let \(E= \bigoplus_{\sigma\in\Sigma} E_\sigma\) be its orthogonal decomposition. Then the following are equivalent: (i) \(E\) is a NHS. (ii) Each closed subspace has a closed complement. (iii) No subspace of \(E\) is linearly homeomorphic to \(c_0\). (iv) Each bounded subset of \(E\) is a compactoid. (v) Each \(E_\sigma\) is finite-dimensional. (vi) If \(\lambda_1,\lambda_2,\dots\in K\) are such that \(n\to\|\lambda_n e_n\|\) is bounded above then \(\lim_{n\to\infty} \lambda_n e_n= 0\). (vii) Each orthogonal sequence in \(E\) which is bounded above tends to \(0\). (viii) Each strictly decreasing orthogonal sequence in \(E\) tends to \(0\). Theorem 4.9: The dual of a NHS is an NHS and NHS are reflexive.

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Keywords

\(K\)-Banach space, norm Hilbert spaces, countable type, closed complement, orthogonal decomposition, Summability and bases; functional analytic aspects of frames in Banach and Hilbert spaces, Operator theory over fields other than \(\mathbb{R}\), \(\mathbb{C}\) or the quaternions; non-Archimedean operator theory, orthogonal base, NHS, Hilbert and pre-Hilbert spaces: geometry and topology (including spaces with semidefinite inner product), Functional analysis over fields other than \(\mathbb{R}\) or \(\mathbb{C}\) or the quaternions; non-Archimedean functional analysis, surjective projection, Hermitian form, Mathematical Physics

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
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