Shell-wise p-adic Duffin–Schaeffer zero-one law

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Let ψ:N→R≥0\psi:\mathbb{N}\to\mathbb{R}_{\geq 0}, let pp be a prime, and let k∈N0k\in\mathbb{N}_0. Let Cnp\mathcal{C}^p_n denote the shell-wise approximation sets and let

Cp=lim sup⁡n→∞Cnp.\mathcal{C}^p=\limsup_{n\to\infty}\mathcal{C}^p_n.

Suppose that

supp⁡ψ⊆pkN∖pk+1N.\operatorname{supp}\psi\subseteq p^k\mathbb{N}\setminus p^{k+1}\mathbb{N}.

Shell-wise p-adic Duffin–Schaeffer conjecture. One should have

μp(Cp∩pkZp×)={(p−1)/pk+1if ∑n=1∞μp(Cnp)=∞,0if ∑n=1∞μp(Cnp)<∞.\mu_p\bigl(\mathcal{C}^p\cap p^k\mathbb{Z}_p^\times\bigr)= \begin{cases} (p-1)/p^{k+1} & \text{if }\displaystyle\sum_{n=1}^{\infty}\mu_p(\mathcal{C}^p_n)=\infty,\\ 0 & \text{if }\displaystyle\sum_{n=1}^{\infty}\mu_p(\mathcal{C}^p_n)<\infty. \end{cases}

This is proposed as a shell-wise Cp\mathcal{C}^p-variant of the p-adic Duffin–Schaeffer theorem. The paper presents it as plausible and does not provide a proof or resolution.

References

Primary source

Mathias Løkkegaard Laursen, “Attainable measures for certain types of p-adic Duffin–Schaeffer sets”, arXiv:2212.03619 (2023).

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