Density-regularity characterization by computable positive-density sets

Let RR be a computable integral domain. Let dd^* denote upper additive density and d×d^*_{\times} upper multiplicative density, and let IADRRIADR_R and IMDRRIMDR_R denote injective additive and multiplicative density regularity, respectively.

Density-regularity characterization conjecture. There exists a computable collection {Bn}n=1\{B_n\}_{n=1}^{\infty} of subsets of R{0}R\setminus\{0\} such that

d(Bn)>0(d×(Bn)>0),d^*(B_n)>0\quad\bigl(d^*_{\times}(B_n)>0\bigr),

and

pIADRR(pIMDRR)for every nN, p has an injective root in Bn.p\in IADR_R\quad\bigl(p\in IMDR_R\bigr)\quad\Longleftrightarrow\quad\text{for every }n\in\mathbb{N},\ p\text{ has an injective root in }B_n.

The computability requirement asks for an algorithm deciding, from nNn\in\mathbb{N} and rR{0}r\in R\setminus\{0\}, whether rBnr\in B_n. The assertion is presented as a further conjectural characterization of density regularity; its general validity remains open.

Sources & referencesView supporting material

Primary source

Sohail Farhangi, Steve Jackson and Bill Mance, “Undecidability in the Ramsey theory of polynomial equations and Hilbert's tenth problem”, arXiv:2412.14917 (2025).

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