arXiv:2205.09205v2

Extensions of invariant random orders on groups

Yair Glasner, Yuqing Frank Lin, Tom Meyerovitch

math.DSmath.GR20F6037A15

Abstract

In this paper we study the action of a countable group ΓΓ on the space of orders on the group. In particular, we are concerned with the invariant probability measures on this space, known as invariant random orders. We show that for any countable group the space of random invariant orders is rich enough to contain an isomorphic copy of any free ergodic action, and characterize the non-free actions realizable. We prove a Glasner-Weiss dichotomy regarding the simplex of invariant random orders. We also show that the invariant partial order on SL3(Z)\mathrm{SL}_3(\mathbf{Z}) corresponding to the semigroup of positive matrices cannot be extended to an invariant random total order. We thus provide the first example for a partial order (deterministic or random) that cannot be randomly extended.

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Audit summary

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.

Current report

Detailed mathematical audit

Generated August 18, 2026
01Statements2 reported findingsCorrect

The extension and nonextension results for invariant random orders, the specification criterion, and the Poulsen-simplex consequences are correct in the revised version.

Main extension, specification, and simplex resultsCorrect

Invariant random orders are characterized with the stated group hypotheses

Sections 4–7 · arXiv:2205.09205v2

The restriction maps are affine and equivariant on the compact spaces of orders. The constructed partial order for the SL3\mathrm{SL}_3 example has no invariant extension by the stated stabilizer obstruction. In the positive direction, separated finite patterns can be amalgamated by the specification construction, and periodic approximants are dense enough to make the nontrivial invariant-order simplex Poulsen under the announced hypotheses. The version-2 qualification for the amenable case is included in the statements.

Full paper, version 2
Theorem 3.1 and the specification resultsCorrect

The higher-rank obstruction and the rich amenable examples occupy distinct regimes

Sections 3 and 5–7 · arXiv:2205.09205v2

For SLn(Z)SL_n(\mathbb Z) the invariant-order relations force an almost-sure sign cycle and hence nonexistence. In the later construction, compatible finite order patterns can instead be pasted with buffers, yielding specification and the stated Poulsen-simplex consequences under their explicit hypotheses.

02Proofs2 reported findingsCorrect

The revised proofs are correct and complete, including the corrected selection argument highlighted by the authors.

Sections 5–7Correct and complete

The amended measurable selection and specification arguments close

Pages 12–22 · Sections 5–7 and version-2 revision note · arXiv:2205.09205v2

Finite order patterns are extended on disjoint translates before averaging, so no inconsistent comparisons are introduced. The measurable selection is applied to a nonempty compact-valued equivariant correspondence in the form stated in version 2. The approximation of invariant laws is weak-star and preserves invariance, which is enough for the simplex conclusions.

Theorem 3.1 and revised Proposition 6.3Correct and complete

Null-set bookkeeping and the corrected pattern-selection step both close

Pages 8–15 and Section 6 · arXiv:2205.09205v2

The matrix contradiction intersects only the countably many full-measure invariant events actually used. Version 2 separately replaces the published Proposition 6.3 selection step with compatible finite patterns before compactness is invoked; every required relation is thus preserved in the limiting invariant measure.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2205.09205v2
Authors listed
Yair Glasner, Yuqing Frank Lin, Tom Meyerovitch
Audit date
August 18, 2026
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