Approximation theorems for uniformly continuous functions

Author:

Hager Anthony W.

Abstract

Let X be a set, A a family of real-valued functions on X which contains the constants, μ A {\mu _A} the weak uniformity generated by A, and U ( μ A X ) U({\mu _A}X) the collection of uniformly continuous functions to the real line R. The problem is how to construct U ( μ A X ) U({\mu _A}X) from A. The main result here is: For A a vector lattice, the collection of suprema of countable, finitely A-equiuniform, order-one subsets of A + {A^ + } is uniformly dense in U ( μ A X ) U({\mu _A}X) . Two less technical corollaries: If A is a vector lattice (resp., vector space), then the collection of functions which are finitely A-uniform and uniformly locally-A (resp., uniformly locally piecewise-A) is uniformly dense in U ( μ A X ) U({\mu _A}X) . Further, for any A, a finitely A-uniform function is just a composition F ( a 1 , , a p ) F \circ ({a_1}, \ldots ,{a_p}) for some a 1 , , a p A {a_1}, \ldots ,{a_p} \in A and F uniformly continuous on the range of ( a 1 , , a p ) ({a_1}, \ldots ,{a_p}) in R p {R^p} . Thus, such compositions are dense in U ( μ A X ) U({\mu _A}X) . For B U ( μ A X ) BU({\mu _A}X) , the compositions with F B U ( R p ) F \in BU({R^p}) are dense (B denoting bounded functions). So, in a sense, to know U ( μ A X ) U({\mu _A}X) it suffices to know A and subspaces of the spaces R p {R^p} , and to know B U ( μ A X ) BU({\mu _A}X) , A and the spaces R p {R^p} suffice.

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

Reference9 articles.

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1. Generation of the uniformly continuous functions;Topology and its Applications;2004-02

2. Some density results for uniformly continuous functions;Topology and its Applications;1997-06

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