Abstract

In the context of (not necessarily minimal) actions, we consider the mean diameter and use it to characterize regular factor maps. Building on this characterization, we prove that an action is diam-mean equicontinuous if and only if it is a regular extension of its maximal equicontinuous factor. Furthermore, we establish the existence of a maximal diam-mean equicontinuous factor and discuss stability properties of regular factor maps. For this, we work in the context of actions of locally compact and σσ-compact amenable groups.

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Audited against arXiv v2

Not a correctness certificate. A “Correct” result may include yellow typos or minor formal corrections that do not affect substantive soundness. It means this audit found no unresolved substantive error under the stated criteria; it does not replace expert scrutiny or formal verification.

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Detailed mathematical audit

Generated August 18, 2026
01Statements3 reported findingsCorrect

The characterizations of regular extensions by diameter-mean proximality, of regular maximal equicontinuous factors by diameter-mean equicontinuity, and the construction of the maximal diameter-mean-equicontinuous factor are correct.

Theorems 1.1–1.2 and 5.2Correct

Mean diameter and regularity characterize the factor structure

Pages 2–5 and 14–19 · Theorems 1.1–1.2 and 5.2 · arXiv:2510.22484v2

Regularity makes almost every fibre a singleton; the invariant fibre-diameter function and the ergodic theorem turn this into vanishing mean diameter. Conversely, diameter-mean proximality forces the nonsingleton-fibre set to have zero invariant measure. The product construction preserves the defining estimates coordinatewise and yields the announced maximal factor, while Proposition 8.2 correctly handles composition of regular extensions.

Full paper, version 2
Theorems 1.1–1.2Correct

Regularity is equivalent to the appropriate mean-diameter condition

Pages 2–5 and Sections 4–6 · arXiv:2510.22484v2

For an extension, singleton fibres almost everywhere are equivalent to vanishing averaged fibre diameter, giving diameter-mean proximality. Applied to the maximal equicontinuous factor, the same criterion becomes diameter-mean equicontinuity. The statements retain minimality and the invariant-measure hypotheses needed in the converse direction.

Theorem 5.2 and Proposition 8.2Correct

A maximal diameter-mean-equicontinuous factor exists and regularity composes

Pages 14–25 · product construction and composition theorem · arXiv:2510.22484v2

The diagonal product of all qualifying factors is again diameter-mean equicontinuous because the product metric has summable coordinate weights. Its universal factor property follows coordinatewise. The later composition result correctly shows that regularity is preserved through the factor chain used in the maximality argument.

02Proofs3 reported findingsCorrect

The fibre, invariant-measure, Følner-average, and factor-composition arguments are correct and complete.

Sections 4–8Correct and complete

The fibre-diameter estimates close in both directions

Pages 10–25 · Sections 4–8 · arXiv:2510.22484v2

Upper semicontinuity of fibre diameter supplies the needed measurable sets, invariant-measure decompositions justify the almost-everywhere claims, and the arguments use temperedness only where a pointwise ergodic theorem is invoked. Countable products are metrized with summable coordinate weights, so finite-coordinate control gives the required global mean estimate.

Sections 4–6Correct and complete

Fibre regularity and mean diameter are converted in both directions

Pages 10–19 · proofs of Theorems 1.1–1.2 · arXiv:2510.22484v2

The fibre-diameter function is upper semicontinuous and hence measurable. The pointwise ergodic theorem converts its zero integral into zero orbit average, while a positive-measure nonsingleton-fibre set gives a positive lower mean on an invariant component. This proves both implications without changing measures or exceptional sets.

Sections 7–8Correct and complete

The countable-product and composition constructions preserve the estimates

Pages 19–25 · maximal factor and regular-composition proofs · arXiv:2510.22484v2

Finite-coordinate truncation controls the summable product metric uniformly, and each retained coordinate has the required mean-diameter estimate. For composition, disintegration shows that singleton fibres persist on a full-measure set, which supplies the regularity statement used by the universal construction.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2510.22484v2
Authors listed
Till Hauser
Audit date
August 18, 2026
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