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2010.03117

Boundary and rigidity of nonsingular Bernoulli actions

Kei Hasegawa, Yusuke Isono, Tomohiro Kanda

correcthigh confidence
Category
Not specified
Journal tier
Strong Field
Processed
Sep 28, 2025, 12:55 AM

Audit review

The paper proves exactly the claimed statement: for a countable exact group G, a two-point nonsingular Bernoulli action satisfying Kakutani’s condition and the finiteness condition ph = pgh for all but finitely many h (for each fixed g) is solid (Theorem A) , with the intended meaning of solidity for subequivalence relations spelled out in the introduction . The model’s solution cites this theorem and outlines the same proof strategy via boundary amenability on anti-symmetric Fock spaces and an AO-type condition for the reduced crossed product, as in the paper’s abstract and strategy sections . Minor omission: the model did not explicitly state the paper’s ‘no atoms’ assumption on (Ω, μ) that appears alongside Kakutani’s condition in Theorem A and in the Kakutani criterion discussion . Apart from that, the logic and match of hypotheses are correct.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} strong field

\textbf{Justification:}

The work delivers the first general solidity results for nonsingular Bernoulli actions using a boundary amenability approach tailored to the non-pmp setting. It bridges an important gap between the measure-preserving rigidity program and type III actions. While the exposition is largely clear, the key AO-type argument is technically involved; a few additional explanations and examples would make the presentation more accessible.