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2008.08471

Topological dynamics beyond Polish groups

Gianluca Basso, Andy Zucker

correctmedium confidence
Category
Not specified
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:55 AM

Audit review

The paper proves the equivalence of (1) CAP, (2) strongly CAP, (3) closedness of AP(Lip(d)) for all continuous right-invariant diameter-1 pseudometrics d, and (4) UEB on M(G), via (2)⇒(1)⇒(3), (4)⇒(2), and the contrapositive ¬(4)⇒¬(3); it also identifies the UEB uniformity with the one generated by the entourages [Lip(d), ε] on S(G) (Proposition 4.19), thereby giving several interchangeable descriptions of the same uniform structure . The candidate solution directly supplies a clean new argument for (3)⇒(1) using the Lipschitz test X→Lip(dψ) and then appeals to the paper’s Theorem 6.1 for the remaining implications, matching the paper’s main theorem. One minor technical slip is the claim that, for a UEB set H, the gauge pseudometric dH(g,h):=sup_{f∈H}|f(g)−f(h)| is right-invariant; without additional H-invariance assumptions this is not automatic. The uniformity identification is nevertheless correct as stated in the paper (Proposition 4.19), which the solution also cites. Net: the paper’s argument is correct and complete; the model’s solution is correct in substance, offers a different proof of (3)⇒(1), and has only a minor fixable detail in Step B.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The manuscript isolates CAP as a robust, topology-agnostic analogue of metrizability of M(G) and proves an elegant equivalence with a canonical UEB uniformity on M(G). The range of characterizations (dynamical, uniform, and metric) is valuable and the closure properties are well-developed. The central uniformity identification on S(G) and the equivalence (1)–(4) are convincingly executed. I recommend minor revisions for small presentational clarifications (e.g., cross-referencing, minor numbering consistency) and for briefly flagging where earlier arguments (e.g., CAP in the metrizable case) are corrected as noted by the authors.