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CorollaryStatement: AI-adaptedProof: AI-adaptedSession-authored (Fable 5 assisted)precheck passverified 2026-08-09 (gpt-5.6-terra-codex-subscription)
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  • AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
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Every continuous map from a nonempty compact Hausdorff space to a uniform space is uniformly continuous

Statement

Every continuous map from a nonempty compact Hausdorff space to a uniform space is uniformly continuous.

Facts & Assumptions

Given: A continuous map f:XYf:X\to Y with XX nonempty compact Hausdorff and YY uniform.

[L1]

A compact Hausdorff space has one compatible uniformity (A nonempty compact Hausdorff space carries exactly one compatible uniformity).

[L2]

Continuity means that every neighbourhood of f(x)f(x) contains the image of some neighbourhood of xx, while uniform continuity is the entourage condition (Continuity of a map of topological spaces at a point and globally, Uniformly continuous map between uniform spaces).

[L3]

Every entourage ball is a neighbourhood in the induced topology (The sets containing an entourage ball about each of their points form a topology). Every open cover of a nonempty compact Hausdorff space is uniform (The covers admitting an open refinement form a compatible uniform-cover structure on a nonempty compact Hausdorff space; in particular every open cover is uniform), and every uniform cover has an entourage-ball cover refining it (On a nonempty set, entourage uniformities and uniform-cover structures determine one another); every target entourage has a symmetric square root (Every uniformity has a base of symmetric entourages).

Proof

technique · direct
1.1

Let VV be a target entourage and choose a symmetric WW with W1W=W2VW^{-1}\circ W=W^{\circ2}\subseteq V. For each xXx\in X, let OxO_x be the union of all open sets OO such that xOx\in O and f[O]W[f(x)]f[O]\subseteq W[f(x)]. Continuity makes this family nonempty, and its union is an open neighbourhood of xx satisfying f[Ox]W[f(x)]f[O_x]\subseteq W[f(x)].

L2L3construct
2.1

The open cover (Ox)xX(O_x)_{x\in X} is uniform by [L3]. Hence there is a source entourage EE whose ball cover refines it: for each aXa\in X, some OxO_x contains E[a]E[a].

step 1.1L1L3
3.1

If (a,b)E(a,b)\in E, then a,bE[a]Oxa,b\in E[a]\subseteq O_x for some xx. Thus f(a),f(b)W[f(x)]f(a),f(b)\in W[f(x)], so (f(a),f(b))W1WV(f(a),f(b))\in W^{-1}\circ W\subseteq V. This is uniform continuity.

step 1.1step 2.1L2

Depends on

Used by

Dependency tree · next 3 levels

Direct dependencies and their dependencies through the next three levels: 35 results over 13 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