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The theorem is named for the mathematicians Hans Hahn and Stefan Banach, who proved it independently in the late 1920s.The special case of the theorem for the space [,] of continuous functions on an interval was proved earlier (in 1912) by Eduard Helly, [1] and a more general extension theorem, the M. Riesz extension theorem, from which the Hahn–Banach theorem can be derived, was proved in ...
Closed graph theorem (functional analysis) – Theorems connecting continuity to closure of graphs; Continuous linear operator; Densely defined operator – Function that is defined almost everywhere (mathematics) Hahn–Banach theorem – Theorem on extension of bounded linear functionals
A TVS Y has the extension property [1] if for every locally convex space X and every vector subspace M of X, Y has the extension property from M to X. A Banach space Y has the metric extension property [1] if for every Banach space X and every vector subspace M of X, Y has the metric extension property from M to X. 1-extensions
Together with the Hahn–Banach theorem and the open mapping theorem, it is considered one of the cornerstones of the field. In its basic form, it asserts that for a family of continuous linear operators (and thus bounded operators ) whose domain is a Banach space , pointwise boundedness is equivalent to uniform boundedness in operator norm .
The Hahn–Banach theorem asserts that φ can be extended to a linear functional on V that is dominated by N. To derive this from the M. Riesz extension theorem, define a convex cone K ⊂ R×V by = {(,) ()}. Define a functional φ 1 on R×U by
In functional analysis, the open mapping theorem, also known as the Banach–Schauder theorem or the Banach theorem [1] (named after Stefan Banach and Juliusz Schauder), is a fundamental result that states that if a bounded or continuous linear operator between Banach spaces is surjective then it is an open map.
Hahn decomposition theorem (measure theory) Hahn embedding theorem (ordered groups) Hairy ball theorem (algebraic topology) Hahn–Banach theorem (functional analysis) Hahn–Kolmogorov theorem (measure theory) Hahn–Mazurkiewicz theorem (continuum theory) Hajnal–Szemerédi theorem (graph theory) Hales–Jewett theorem (combinatorics)
Any Banach limit on is an example of an element of the dual Banach space of which is not in . The dual of ℓ ∞ {\displaystyle \ell ^{\infty }} is known as the ba space , and consists of all ( signed ) finitely additive measures on the sigma-algebra of all subsets of the natural numbers , or equivalently, all (signed) Borel measures on the ...