Metric geometry | Hilbert space | Lipschitz maps | Theorems in real analysis | Theorems in functional analysis

Kirszbraun theorem

In mathematics, specifically real analysis and functional analysis, the Kirszbraun theorem states that if U is a subset of some Hilbert space H1, and H2 is another Hilbert space, and is a Lipschitz-continuous map, then there is a Lipschitz-continuous map that extends f and has the same Lipschitz constant as f. Note that this result in particular applies to Euclidean spaces En and Em, and it was in this form that Kirszbraun originally formulated and proved the theorem. The version for Hilbert spaces can for example be found in (Schwartz 1969, p. 21). If H1 is a separable space (in particular, if it is a Euclidean space) the result is true in Zermelo–Fraenkel set theory; for the fully general case, it appears to need some form of the axiom of choice; the Boolean prime ideal theorem is known to be sufficient. The proof of the theorem uses geometric features of Hilbert spaces; the corresponding statement for Banach spaces is not true in general, not even for finite-dimensional Banach spaces. It is for instance possible to construct counterexamples where the domain is a subset of with the maximum norm and carries the Euclidean norm. More generally, the theorem fails for equipped with any norm (Schwartz 1969, p. 20). (Wikipedia).

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Introduction to additive combinatorics lecture 10.8 --- A weak form of Freiman's theorem

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From playlist Introduction to Additive Combinatorics (Cambridge Part III course)

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In this video I present a proof of Plünnecke's theorem due to George Petridis, which also uses some arguments of Imre Ruzsa. Plünnecke's theorem is a very useful tool in additive combinatorics, which implies that if A is a set of integers such that |A+A| is at most C|A|, then for any pair

From playlist Introduction to Additive Combinatorics (Cambridge Part III course)

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From playlist The Integral

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From playlist Mathematics

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From playlist 4th Itzykson Colloquium - Moduli Spaces and Quantum Curves

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From playlist Extreme Value Theorem of Functions

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From playlist Partial Differential Equations

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From playlist Riemann Sum Approximation

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From playlist Introduction to Additive Combinatorics (Cambridge Part III course)

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Calculus 1 (Stewart) Ep 22, Mean Value Theorem (Oct 28, 2021)

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From playlist Math 1171 (Calculus 1) Fall 2021

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From playlist Vector Calculus @ UNSW Sydney. Dr Chris Tisdell

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From playlist Math 3371 (Real analysis) Fall 2020

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From playlist Geometry

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Wolfram Physics Project: Working Session Sept. 15, 2020 [Physicalization of Metamathematics]

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From playlist Wolfram Physics Project Livestream Archive

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Johnathan Bush (7/8/2020): Borsuk–Ulam theorems for maps into higher-dimensional codomains

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From playlist AATRN 2020

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From playlist Worldwide Single-Variable Calculus for AP®

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From playlist Engineering Math: Vector Calculus and Partial Differential Equations

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From playlist Vector Calculus @ UNSW Sydney. Dr Chris Tisdell

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From playlist Famous Math Problems

Related pages

Uniform norm | Hilbert space | Boolean prime ideal theorem | Banach space | Functional analysis | Real analysis | Mathematics | Separable space | Lipschitz continuity | Euclidean space | Zermelo–Fraenkel set theory | Subset