ArzelÀ–Ascoli Theorem

(Theory)

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What is Arzelà–Ascoli theorem?

The Arzelà–Ascoli theorem is a fundamental result of mathematical analysis giving necessary and sufficient conditions to decide whether every sequence of a given family of real-valued continuous functions defined on a closed and bounded interval has a uniformly convergent subsequence. The main condition is the equicontinuity of the family of functions. The theorem is the basis of many proofs in mathematics, including that of the Peano existence theorem in the theory of ordinary differential equations, Montel's theorem in complex analysis, and the Peter–Weyl theorem in harmonic analysis and various results concerning compactness of integral operators. The notion of equicontinuity was introduced in the late 19th century by the Italian mathematicians Cesare Arzelà and Giulio Ascoli. A weak form of the theorem was proven by , who established the sufficient condition for compactness, and by , who established the necessary condition and gave the first clear presentation of the result. A further generalization of the theorem was proven by , to sets of real-valued continuous functions with domain a compact metric space (p. 382). Modern formulations of the theorem allow for the domain to be compact Hausdorff and for the range to be an arbitrary metric space. More general formulations of the theorem exist that give necessary and sufficient conditions for a family of functions from a compactly generated Hausdorff space into a uniform space to be compact in the compact-open topology; see , page 234).

Technology Types

compactness theoremcontinuous mappingfunctionmathematical relationmathematical theorempropositionstatementtheoremtheorems in analysistheorems in functional analysistheorytopology of function space

Synonyms

Arzela theoremArzela-AscoliArzela-Ascoli theoremArzelà-Ascoli theoremArzelà-Ascoli theorem/ProofsArzela-Ascoli-TheoremArzela–Ascoli theoremArzela's TheoremAscoli theoremAscoli-Arzela theoremAscoli-Arzelà theoremAscoli's Theorem

Translations

Satz von Arzelà-Ascoli (de)Stelling van Arzelà-Ascoli (nl)Teorema de Arzelá-Ascoli (es)Teorema de Arzelà-Ascoli (pt)Teorema di Ascoli-Arzelà (it)Théorème d'Ascoli (fr)Twierdzenie Arzeli-Ascolego (pl)Теорема Асколи — Арцела (ru)Теорема Асколі — Арцела (uk)アスコリ=アルツェラの定理 (ja)阿尔泽拉-阿斯科利定理 (zh)

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