AbsoluteNeighborhoodRetract.lean`

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Annotation provenance. This overlay contains 10 curated AI-written annotations and 7190 mechanical source-derived annotations. They have not been human-reviewed as explanations; treat them as unverified and not mathematical authority. Retained generation history: The 71 original curated annotations were produced in a Claude Sonnet 5.5 session at medium effort; Claude Opus 5.5 is recorded in that session as the advisor model, not the direct author. The bulk source-derived expansion was generated mechanically from pinned source comments by tooling developed in a GPT-5.6 Sol session at ultra reasoning; GPT-5.6 Sol did not originate the quoted source prose. On 2026-10-17 the mechanically generated source-comment annotations of the Formal Conjectures, Carleson, FLT, PFR, CompFiles, Mathematics in Lean and Theorem Proving in Lean overlays were regenerated by the same generator after three corrections made in a Claude Sonnet 5.5 session: titles no longer cut a sentence inside mathematics or end on a dangling word, workflow markers are removed from the quoted prose, and declaration names follow the scanner's namespace resolution. The boilerplate step line was dropped, and comments that were only a row of dashes no longer yield annotations. No new prose was written and no human review is claimed.

Credit: The upstream authors and contributors retain credit for the project and mathematics. lean4-explainer only renders their pinned source and adds the separately disclosed explanation layer.

Project sources: Pinned project documentation, Formal Conjectures paper, arXiv v1

1 declarations, 0 contain sorry, 0 declared as axioms

Imports (3)

Imported by 1 file

FormalConjecturesForMathlib.lean

class IsAbsoluteNeighborhoodRetract Documented declaration: IsAbsoluteNeighborhoodRetract line 35 source
Source documentation
A topological space X is an absolute neighborhood retract (ANR) if, whenever it is embedded as a closed subspace of a normal space Y, there exists a continuous retraction from some open neighborhood of X in Y onto X.
More precisely, for every closed embedding e : X → Y into a normal space Y, there exist an open set U ⊆ Y containing the image of e and a continuous map r : Y → X defined on U such that r ∘ e = id.

standard axioms: Classical.choice, Quot.sound, propext what this means
Statement uses: TopologicalSpace
```
class IsAbsoluteNeighborhoodRetract (X : Type u) [TopologicalSpace X] : Prop where
…
```