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 spaces, with the source disagreement over whether regularity includes stated explicitly