Linear Spaces, Linear Functionals, and the Hahn–Banach Theorem

2018 ◽  
pp. 137-158
Author(s):  
Vladimir Kadets
Keyword(s):  
Linear Functionals ◽  
Linear Spaces ◽  
Banach Theorem

scholarly journals A Hahn-Banach theorem for semifields

1969 ◽  
Vol 10 (1-2) ◽  
pp. 20-22 ◽  
Author(s):  
Martin Kleiber ◽  
W. J. Pervin
Keyword(s):  
Type Theorem ◽  
Linear Functionals ◽  
Linear Spaces ◽  
Banach Theorem ◽  
Real Linear

Iseki and Kasahara (see [3]) have given a Hahn-Banach type theorem for semifield-valued linear functionals on real linear spaces. We shall generalize their result by considering linear spaces over semifields.

scholarly journals Bidual Spaces and Reflexivity of Real Normed Spaces

2014 ◽  
Vol 22 (4) ◽  
pp. 303-311
Author(s):  
Keiko Narita ◽  
Noboru Endou ◽  
Yasunari Shidama
Keyword(s):  
Real Number ◽  
Normed Space ◽  
Uniform Boundedness ◽  
Linear Operators ◽  
Linear Functionals ◽  
Normed Spaces ◽  
Boundedness Theorem ◽  
Natural Mapping ◽  
Real Normed Space ◽  
Banach Theorem

Summary In this article, we considered bidual spaces and reflexivity of real normed spaces. At first we proved some corollaries applying Hahn-Banach theorem and showed related theorems. In the second section, we proved the norm of dual spaces and defined the natural mapping, from real normed spaces to bidual spaces. We also proved some properties of this mapping. Next, we defined real normed space of R, real number spaces as real normed spaces and proved related theorems. We can regard linear functionals as linear operators by this definition. Accordingly we proved Uniform Boundedness Theorem for linear functionals using the theorem (5) from [21]. Finally, we defined reflexivity of real normed spaces and proved some theorems about isomorphism of linear operators. Using them, we proved some properties about reflexivity. These formalizations are based on [19], [20], [8] and [1].

scholarly journals On the extension of linear operators

2001 ◽  
Vol 28 (10) ◽  
pp. 621-623 ◽  
Author(s):  
John J. Saccoman
Keyword(s):  
Extension Theorem ◽  
Linear Operators ◽  
Two Dimensional ◽  
Linear Functionals ◽  
Bounded Linear Operators ◽  
Bounded Linear ◽  
Banach Theorem

It is well known that the Hahn-Banach theorem, that is, the extension theorem for bounded linear functionals, is not true in general for bounded linear operators. A characterization of spaces for which it is true was published by Kakutani in 1940. We summarize Kakutani's work and we give an example which demonstrates that his characterization is not valid for two-dimensional spaces.

The Hahn-Banach theorem for non-Archimedean-valued fields

1952 ◽  
Vol 48 (1) ◽  
pp. 41-45 ◽  
Author(s):  
A. W. Ingleton
Keyword(s):  
Banach Spaces ◽  
Normed Linear Space ◽  
General Theorem ◽  
Sufficient Conditions ◽  
Linear Operators ◽  
Necessary Condition ◽  
Linear Functionals ◽  
Banach Theorem ◽  
Necessary And Sufficient ◽  
Special Case

1. The Hahn-Banach theorem on the extension of linear functionals holds in real and complex Banach spaces, but it is well known that it is not in general true in a normed linear space over a field with a non-Archimedean valuation. Sufficient conditions for its truth in such a space have been given, however, by Monna and by Cohen‡. In the present paper, we show that a necessary condition for the property is that the space be totally non-Archimedean in the sense of Monna, and establish a necessary and sufficient condition on the field for the theorem to hold in every totally non-Archimedean space over the field. This result is obtained as a special case of a more general theorem concerning linear operators, which is analogous to a theorem of Nachbin ((6), Theorem 1) concerning operators in real Banach spaces.

scholarly journals Extension with larger norm and separation with double support in normed linear spaces

1980 ◽  
Vol 21 (1) ◽  
pp. 93-105 ◽  
Author(s):  
Ivan Singer
Keyword(s):  
Convex Sets ◽  
Separation Theorems ◽  
Continuous Linear ◽  
Linear Functionals ◽  
Linear Spaces ◽  
Double Support ◽  
Linear Subspaces ◽  
Normed Linear Spaces ◽  
Whole Space

We prove, in normed linear spaces, the existence of extensions of continuous linear functionals from linear subspaces to the whole space, with arbitrarily prescribed larger norm. Also, we prove that under an additional boundedness assumption, in the known separation theorems for convex sets, there exist hyperplanes which separate and support both sets.

scholarly journals Semiconvex geometry

1981 ◽  
Vol 30 (4) ◽  
pp. 496-510 ◽  
Author(s):  
Joe Flood
Keyword(s):  
Algebraic Variety ◽  
Convex Sets ◽  
Convex Geometry ◽  
Algebraic Approach ◽  
Algebraic Proof ◽  
Linear Spaces ◽  
Structural Decomposition ◽  
Banach Theorem ◽  
Real Linear ◽  
Convex Subsets

AbstractSemiconvex sets are objects in the algebraic variety generated by convex subsets of real linear spaces. It is shown that the fundamental notions of convex geometry may be derived from an entirely algebraic approach, and that conceptual advantages result from applying notions derived from algebra, such as ideals, to convex sets. Some structural decomposition results for semiconvex sets are obtained. An algebraic proof of the algebraic Hahn-Banach theorem is presented.

scholarly journals Integration in Locally Compact Spaces II

1951 ◽  
Vol 3 ◽  
pp. 7-22 ◽  
Author(s):  
Edwin Hewitt ◽  
H. S. Zuckerman
Keyword(s):  
Linear Functional ◽  
Normed Linear Space ◽  
Linear Subspace ◽  
Natural Extension ◽  
Linear Functionals ◽  
Compact Spaces ◽  
Banach Theorem ◽  
Natural Extensions ◽  
Concrete Representations ◽  
Locally Compact Spaces

The general problem of producing concrete representations for continuous linear functionals on normed linear spaces, ie., of identifying conjugate spaces, has of course attracted the attention of many mathematicians during the last five decades and has been solved in many cases [1, pp. 59-72]. Likewise, the problem of extending a linear functional defined on a linear subspace of a normed linear space may be regarded as solved by the Hahn-Banach theorem [1, p. 28], although problems involving “natural” extensions, like that yielding the Lebesgue integral from the Riemann integral, remain. In the present paper, we shall consider two “natural’ methods of extending a certain linear functional and show that they are in fact identical. As a by-product, we obtain a concrete representation both for the original functional and for its “natural” extension. In subsequent communications, the writers will consider topologies in certain families of linear functionals, canonical resolutions of linear functionals, and other extension problems.

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