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DefinitionDefinition: AI-adaptedProof: Not applicableSession-authored (Fable 5 assisted)audited 2026-08-02
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The Samuel uniformity generated by bounded uniformly continuous functions

Definition

Let (X,U)(X,\mathcal U) be a uniform space. Give [0,1][0,1] the subspace metric d[0,1](s,t):=std_{[0,1]}(s,t):=|s-t| obtained by restricting the usual real metric of The absolute value makes R\mathbb{R} a metric space: d(x,y)=xyd(x,y) = |x-y| is a metric, its open balls are the intervals (xr,x+r)(x-r, x+r), and it is unbounded, as licensed by Isometry, isometric embedding, and the subspace metric on a subset, and equip it with the uniformity generated by that metric (A metric on a nonempty set generates an entourage uniformity whose induced topology and uniformly continuous maps are the usual metric notions, and this uniformity is separated). Let FU\mathcal F_{\mathcal U} be the family of all uniformly continuous maps f:X[0,1]f:X\to[0,1] (Uniformly continuous map between uniform spaces). For fFUf\in\mathcal F_{\mathcal U} put

pf(x,y):=f(x)f(y).p_f(x,y):=|f(x)-f(y)|.

The Samuel uniformity US\mathcal U_S is the uniformity generated by the gauge (pf)fFU(p_f)_{f\in\mathcal F_{\mathcal U}} in the sense of A gauge of pseudometrics and, on a nonempty set, the uniformity it generates. Thus a base consists of the sets

E(F,ε)={(x,y):pf(x,y)<ε for every fF},E(F,\varepsilon)=\{(x,y):p_f(x,y)<\varepsilon\text{ for every }f\in F\},

where FFUF\subseteq\mathcal F_{\mathcal U} is finite and ε>0\varepsilon>0.

The well-definedness of this gauge and its relation to U\mathcal U are proved in Samuel function pseudometrics generate a uniformity coarser than the original one . The use of [0,1][0,1] rather than arbitrary bounded real-valued functions is equivalent by affine rescaling, also proved there.

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