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2206.04755

Synchronizing Dynamical Systems: Their Groupoids and C*-Algebras

Robin J. Deeley, Andrew M. Stocker

correcthigh confidence
Category
Not specified
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper proves, for mixing finitely presented systems, (i) amenability of Glc_sync, Glcs, and Glcu; (ii) the ideal exact sequence for A(X,ϕ) with Isync; (iii) a Morita equivalence Isync ≃ S ⊗ U via a bibundle Z; and (iv) simplicity of S, U, and Isync. These are stated and proved in Theorems 5.8, 5.9, 6.9, and 6.10 (and 6.11 in a special case) of the paper. In contrast, the candidate solution crucially asserts that Glcs and Glcu are AF étale groupoids in general and uses this to deduce amenability and simplicity; the paper does not claim AF in this generality and instead proves amenability by lifting to a Smale space and using Borel amenability arguments (Theorem 6.9), then deduces amenability of Glc_sync via the Morita equivalence (Theorem 6.10). The model also omits the density hypotheses needed for the groupoid equivalence Isync ≃ S ⊗ U (explicit in Theorem 5.9 and ensured for finitely presented systems in Lemma 6.7), and it relies on an unsubstantiated “unique splitting” of local conjugacies on product rectangles. Therefore, while the model’s conclusions overlap with the paper’s main theorems, its key steps and assumptions are incorrect or incomplete relative to the paper’s precise hypotheses and proofs. See Theorem 0.1 and Theorems 5.8, 5.9, 6.9, 6.10 in the paper for the correct statements and routes of proof .

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The manuscript successfully generalizes key Smale-space C*-algebraic results to synchronizing systems. The construction of the synchronizing ideal, the bibundle implementation of the Morita equivalence, and the amenability arguments via Smale-space lifts are technically solid and conceptually clear. Only minor presentation issues (typos, cross-references, brief reminders about topology choices) need attention.