arXiv:2607.01896v1

Topologically free minimal actions without dynamical comparison

Paolo Boldrini, Akshara Prasad

math.DSmath.OA37A5506F0546L3503C98

Abstract

We show the existence of a topologically free minimal action of F\mathbb F_\infty on the Cantor space that does not have dynamical comparison. Moreover, we show that this phenomenon can happen both in the presence and in the absence of invariant measures. We also show that strict comparison of the reduced crossed product C*-algebra does not imply dynamical comparison for minimal actions. Our technique involves constructing a monoid which is not almost unperforated, embedding it into a countable refinement monoid and then realising it as the type semigroup associated to a dynamical system.

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Audited against arXiv v1

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.

Current report

Detailed mathematical audit

Generated August 18, 2026
01Statements2 reported findingsCorrect

The constructions of topologically free minimal Cantor actions without dynamical comparison, both with and without invariant probability measures, and the stated crossed-product consequences are correct.

Main construction theoremsCorrect

Minimality and topological freeness coexist with failure of comparison

Pages 3–8 and Sections 3–6 · arXiv:2607.01896v1

The prescribed type semigroups contain elements witnessing failure of the comparison order. The realization theorem produces Cantor actions with those semigroups, and the Baire-category perturbation removes fixed-point interiors while preserving the finite clopen data used for minimality and the obstruction. In the measure-free case the construction eliminates states; in the measured case it retains the announced invariant simplex. The crossed-product conclusion uses strict comparison in the algebraic sense stated, not an unproved converse with dynamical comparison.

Full paper, version 1
Theorems 6.1, 6.10, and 7.4Correct

Minimality, failure of comparison, and crossed-product consequences are correctly separated

Sections 6–7 · arXiv:2607.01896v1

The Fraïssé action is minimal by simplicity of the refinement cone, while a paradoxical element obstructs dynamical comparison. The later Cantor actions inherit these properties under the stated group embeddings, and the operator-algebraic corollaries invoke the additional freeness and simplicity hypotheses explicitly.

02Proofs2 reported findingsCorrect

The monoid realization, Baire-category, freeness, minimality, and comparison-obstruction proofs are correct and complete.

Sections 3–6Correct and complete

The perturbations preserve the obstruction data

Pages 9–28 · Sections 3–6 · arXiv:2607.01896v1

Each dense-open condition concerns only finitely many clopen levels, so the diagonal construction meets all freeness requirements. Refinements are chosen compatibly with the incidence matrices, which preserves minimality and realizes the target ordered monoid. The clopen sets witnessing noncomparison survive the limit and have precisely the measure inequalities claimed.

Sections 5–6Correct and complete

Fraïssé realization and the comparison obstruction both close

Pages 24–43 · arXiv:2607.01896v1

Amalgamation for finite measured Boolean structures produces a homogeneous limit whose type semigroup is the prescribed refinement cone. Simplicity supplies orbit-minimality, while the chosen noncancellative/paradoxical relation survives the realization and directly contradicts the comparison inequality.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2607.01896v1
Authors listed
Paolo Boldrini, Akshara Prasad
Audit date
August 18, 2026
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