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OP-6966Status unassessedGeometry and topology

Weakly First Countable Compact Hausdorff Spaces That Are Not First Countable

TheoremDB P9490 · Candidate awaiting source review

Source candidate · not reviewedAs of 2026-09-08Source & evidence ↓

Problem statement

A topological space XX is called weakly first countable if there exists a function V:X→N→P(X)V : X \to \mathbb{N} \to \mathcal{P}(X) such that: (i) for every x∈Xx \in X and n∈Nn \in \mathbb{N}, we have x∈V(x,n)x \in V(x,n); (ii) for every x∈Xx \in X and n∈Nn \in \mathbb{N}, V(x,n+1)⊆V(x,n)V(x,n+1) \subseteq V(x,n); and (iii) a subset O⊆XO \subseteq X is open if and only if for every x∈Ox \in O there exists k∈Nk \in \mathbb{N} such that V(x,k)⊆OV(x,k) \subseteq O. A topological space is first countable if every point has a countable neighborhood basis. Does there exist in ZFC a weakly first countable compact Hausdorff space that is not first countable?

Lean 4

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Formal statement

Lean 4
theorem existsWeaklyFirstCountableCompactNotFirstCountable :
    ∃ (X : Type) (_ : TopologicalSpace X),
      WeaklyFirstCountableTopology X ∧ CompactSpace X ∧ T2Space X ∧
        ¬ FirstCountableTopology X

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Proofs & verification

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Progress & source assessment

Source-reported assessment, retrieved 8 September 2026. Frontier Science has not independently reviewed this status.

Open. No signed Lean verification is attached to this problem or its selected resolution.

This record is in the source backlog; its novelty and unresolved status have not passed source review.

References
  1. [1]TheoremDB P9490 link
  2. [2]Source formal statement (not locally verified) link

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