How statement and proof provenance work
The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
- Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
- AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
- AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.
These labels describe origin, not correctness: citations and verification chips remain separate evidence.
Every paracompact Hausdorff space is regular
Statement
Every paracompact Hausdorff topological space is regular. No choice principle is used.
Facts & Assumptions
Given: A paracompact Hausdorff space , a closed set , and a point .
Distinct points in a Hausdorff space have disjoint open neighbourhoods (Hausdorff space: distinct points have disjoint open neighbourhoods; every metrizable space is Hausdorff and the indiscrete topology on two points is not).
A paracompact space gives every open cover a locally finite open refining cover (Paracompactness: every open cover has a locally finite open refinement, with no separation axiom built into the word).
For a locally finite family, closure commutes with union (Locally finite families remain locally finite after taking closures, closure commutes with their union, and a locally finite union of closed sets is closed).
Regularity is separation of a point from a disjoint closed set by disjoint open sets (Regular spaces and spaces, with the source disagreement over whether regularity includes stated explicitly).
Proof
For every , Hausdorffness gives disjoint open sets with and ; hence , since is closed and contains . Thus the family of all open with and , together with , is an open cover of .
Take a locally finite open cover refining , and put .
The set is open and contains : a member of containing a point of cannot refine , so it occurs in the defining union.
Every occurring in lies in an eligible of step 1.1, so ; local finiteness and [L1] give , whence .
The open sets and contain and respectively and are disjoint. By [F3], is regular.
Depends on
- Paracompactness: every open cover has a locally finite open refinement, with no separation axiom built into the word
- Refinements, locally finite families, point-finite families, and star refinements
- Locally finite families remain locally finite after taking closures, closure commutes with their union, and a locally finite union of closed sets is closed
- Hausdorff space: distinct points have disjoint open neighbourhoods; every metrizable space is Hausdorff and the indiscrete topology on two points is not
- Regular spaces and $T_3$ spaces, with the source disagreement over whether regularity includes $T_1$ stated explicitly
Used by
- Under choice, every open cover of a paracompact Hausdorff space has locally finite open refinements {Vₛ} and {Wₛ} with overlineVₛ⊆ Wₛ⊆overlineWₛ⊆ Uₛ Lemma
- Every paracompact Hausdorff space is normal Theorem
- Under choice, a space is metrizable if and only if it is paracompact, Hausdorff, and locally metrizable Theorem
Dependency tree · next 3 levels
Direct dependencies and their dependencies through the next three levels: 52 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
- Dartmouth Point-Set Topology, Lecture 25 (standard reference, not scraped)
- Topology 262 notes (California State University, Northridge) (standard reference, not scraped)