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Assuming dependent choice, every entourage uniformity is generated by a gauge of uniformly continuous pseudometrics
Statement
Assuming dependent choice, every entourage uniformity is generated by a gauge of uniformly continuous pseudometrics.
Facts & Assumptions
Given: An entourage uniformity and dependent choice.
For every entourage, dependent choice supplies a normal sequence whose first nontrivial member is contained in that entourage (Assuming dependent choice, every entourage admits a normal symmetric sequence subordinate to it).
Such a sequence yields a uniformly continuous pseudometric whose dyadic balls lie between consecutive entourages (A normal sequence of entourages yields a uniformly continuous pseudometric with controlled dyadic balls).
A gauge generates the filter based on finite simultaneous pseudometric balls (A gauge of pseudometrics and, on a nonempty set, the uniformity it generates).
Proof
Let be the set of all pseudometrics obtained by applying [L2] to normal sequences of [L1] subordinate to some entourage. This definition makes no simultaneous choice. Every is uniformly continuous for , and for each entourage , [L1] and [L2] ensure that at least one has a positive-radius -ball contained in .
For each and each positive radius, its ball is an original entourage by step 1.1. Hence every finite intersection defining a basic entourage of the gauge belongs to .
Conversely every original entourage contains a positive-radius ball for at least one by step 1.1, so it belongs to the gauge uniformity.
The two uniformities contain one another and are equal.
Depends on
- A gauge of pseudometrics and, on a nonempty set, the uniformity it generates
- Assuming dependent choice, every entourage admits a normal symmetric sequence subordinate to it
- A normal sequence of entourages yields a uniformly continuous pseudometric with controlled dyadic balls
- The axiom of dependent choice: a relation in which every element is related to something admits an $\mathbb{N}$-indexed chain
Used by
Dependency tree · next 3 levels
Direct dependencies and their dependencies through the next three levels: 90 results over 20 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
- J. Wodzicki, Uniform Structure (standard reference, not scraped)
- M. Kunzinger, General Topology (standard reference, not scraped)