COMPACT-RANGE VIETORIS POWERS OF COUNTABLE ORDINALS

For every ordinal ω < α < ω1, the ordered compact-set space K(α, ord) of Caruvana andHolshouser is second-countable and Lindelo¨f, but neither σ-compact nor Menger. This answersQuestion 2.18 of their published paper. We first prove that a second-countable ground space has asecond-countable compact-range Vietoris power at countable index. A delayed diagonal then showsthat the closed family of surjections onto ω + 1 with zeroth coordinate ω is not σ-compact. Closedinclusions induce closed embeddings at a fixed index, so this obstruction transfers to every ordinal inthe stated interval. Explicit coordinate covers yield the non-Menger conclusion. The proofs areself-contained, consolidate the earlier convergent-sequence case with its generalization, and areaccompanied by a Lean 4 formalization of the principal ordinal theorem.

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Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-10-15
DOI
https://doi.org/10.5281/zenodo.23405744
Primary Topic
Advanced Topology and Set Theory
Type
article
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article

COMPACT-RANGE VIETORIS POWERS OF COUNTABLE ORDINALS

Lucas Alves de Almeida
Zenodo (CERN European Organization for Nuclear Research)
Advanced Topology and Set Theory
article

COMPACT-RANGE VIETORIS POWERS OF COUNTABLE ORDINALS

Lucas Alves de Almeida
article en

Abstract

For every ordinal ω < α < ω1, the ordered compact-set space K(α, ord) of Caruvana andHolshouser is second-countable and Lindelo¨f, but neither σ-compact nor Menger. This answersQuestion 2.18 of their published paper. We first prove that a second-countable ground space has asecond-countable compact-range Vietoris power at countable index. A delayed diagonal then showsthat the closed family of surjections onto ω + 1 with zeroth coordinate ω is not σ-compact. Closedinclusions induce closed embeddings at a fixed index, so this obstruction transfers to every ordinal inthe stated interval. Explicit coordinate covers yield the non-Menger conclusion. The proofs areself-contained, consolidate the earlier convergent-sequence case with its generalization, and areaccompanied by a Lean 4 formalization of the principal ordinal theorem.

Zenodo (CERN European Organization for Nuclear Research)
Openalex Percentile: Top 8%
Advanced Topology and Set Theory
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