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In mathematics, the Fraňková–Helly selection theorem is a generalisation of Helly's selection theorem for functions of bounded variation to the case of regulated functions. It was proved in 1991 by the Czech mathematician Dana Fraňková. ==Background== Let ''X'' be a separable Hilbert space, and let BV((''T'' ); ''X'') denote the normed vector space of all functions ''f'' : (''T'' ) → ''X'' with finite total variation over the interval (''T'' ), equipped with the total variation norm. It is well known that BV((''T'' ); ''X'') satisfies the compactness theorem known as Helly's selection theorem: given any sequence of functions (''f''''n'')''n''∈N in BV((''T'' ); ''X'') that is uniformly bounded in the total variation norm, there exists a subsequence : and a limit function ''f'' ∈ BV((''T'' ); ''X'') such that ''f''''n''(''k'')(''t'') converges weakly in ''X'' to ''f''(''t'') for every ''t'' ∈ (''T'' ). That is, for every continuous linear functional ''λ'' ∈ ''X'' *, : Consider now the Banach space Reg((''T'' ); ''X'') of all regulated functions ''f'' : (''T'' ) → ''X'', equipped with the supremum norm. Helly's theorem does not hold for the space Reg((''T'' ); ''X''): a counterexample is given by the sequence : One may ask, however, if a weaker selection theorem is true, and the Fraňková–Helly selection theorem is such a result. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Fraňková–Helly selection theorem」の詳細全文を読む スポンサード リンク
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