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The Samuel uniformity generated by bounded uniformly continuous functions
Definition
Let be a uniform space. Give the subspace metric obtained by restricting the usual real metric of The absolute value makes a metric space: is a metric, its open balls are the intervals , 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 be the family of all uniformly continuous maps (Uniformly continuous map between uniform spaces). For put
The Samuel uniformity is the uniformity generated by the gauge in the sense of A gauge of pseudometrics and, on a nonempty set, the uniformity it generates. Thus a base consists of the sets
where is finite and .
The well-definedness of this gauge and its relation to are proved in Samuel function pseudometrics generate a uniformity coarser than the original one ↗. The use of rather than arbitrary bounded real-valued functions is equivalent by affine rescaling, also proved there.
Depends on
- A gauge of pseudometrics and, on a nonempty set, the uniformity it generates
- Uniformly continuous map between uniform spaces
- Intervals of $\mathbb{R}$: the nine order-convex forms, nondegeneracy, and length
- The absolute value makes $\mathbb{R}$ a metric space: $d(x,y) = |x-y|$ is a metric, its open balls are the intervals $(x-r, x+r)$, and it is unbounded
- Isometry, isometric embedding, and the subspace metric on a subset
- 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
Used by
- The Samuel completion and, when compactifying, the Samuel compactification Definition
- The Samuel reflection of a nonempty indiscrete uniform space is a singleton Example
- Assuming dependent choice, a totally bounded uniformity equals its Samuel uniformity Lemma
- Assuming dependent choice, the Samuel uniformity induces the original topology Lemma
- Samuel function pseudometrics generate a uniformity coarser than the original one Lemma
- The Samuel uniformity is totally bounded Lemma
- Under dependent choice and the ultrafilter lemma, uniformly continuous maps to compact Hausdorff spaces extend uniquely over the Samuel compactification Theorem
Dependency tree · next 3 levels
Direct dependencies and their dependencies through the next three levels: 49 results over 12 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.
Sources
- Garrido and Meroño, The Samuel realcompactification (standard reference, not scraped)
- J. Wodzicki, Uniform Structure (standard reference, not scraped)