Bergelson’s partition-regularity question for nice recurrence

A set RN>0R\subseteq\mathbb{N}_{>0} is called a set of nice recurrence if, for every measure-preserving system (X,μ,T)(X,\mu,T), every measurable set AXA\subseteq X, and every ε>0\varepsilon>0, there exists nRn\in R such that μ(ATnA)μ(A)2ε\mu(A\cap T^{-n}A)\geq\mu(A)^2-\varepsilon. The problem asks whether, for every set of nice recurrence RR and every finite coloring c:R{1,,k}c:R\to\{1,\ldots,k\}, there exists a color i{1,,k}i\in\{1,\ldots,k\} such that the monochromatic set Ri={nR:c(n)=i}R_i=\{n\in R:c(n)=i\} is itself a set of nice recurrence.

Progress summary

Solved

A new preprint claims that every finite coloring contains the required same-colored set, but the claim has not yet been independently verified.

The question asks whether the required monochromatic nice-recurrence subset exists for every finite coloring.

August 2026 preprint claim

A preprint titled “Sets of nice recurrence are partition regular” claims to establish the required subset for every finite coloring, which would settle the question. The result remains an unverified preprint claim.

Current status (as of August 2026): A preprint claims the question is solved for every finite coloring, but independent verification is not recorded.

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Primary source

arXiv

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