Hausdorff measure Duffin–Schaeffer conjecture

From papers

Let kNk\in\mathbb{N}, let ff be a dimension function such that rkf(r)r^{-k}f(r) is monotonic, and let Ak(ψ)[0,1]k\mathcal{A}_k”(\psi)\subset[0,1]^k be the set of simultaneously reduced ψ\psi-well approximable points. Let φ\varphi denote Euler's totient function and let Hf\mathcal{H}^f be the Hausdorff ff-measure. Hausdorff measure Duffin–Schaeffer conjecture. For every approximating function ψ:NR0\psi:\mathbb{N}\to\mathbb{R}_{\geq 0},

Hf(Ak(ψ))={0if q=1f(ψ(q)q)φ(q)k<,Hf([0,1]k)if q=1f(ψ(q)q)φ(q)k=.\mathcal{H}^f(\mathcal{A}_k”(\psi))=\begin{cases}0&\text{if }\displaystyle\sum_{q=1}^{\infty}f\left(\frac{\psi(q)}q\right)\varphi(q)^k<\infty,\\\\[2ex]\mathcal{H}^f([0,1]^k)&\text{if }\displaystyle\sum_{q=1}^{\infty}f\left(\frac{\psi(q)}q\right)\varphi(q)^k=\infty. \end{cases}

This is the Hausdorff-measure generalisation of the one-dimensional and higher-dimensional Duffin–Schaeffer conjectures presented by Beresnevich and Velani; the supplied text does not state whether it has been resolved in this full form.

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Sources & referencesView supporting material

Primary source

Demi Allen and Edouard Daviaud, “A survey of recent extensions and generalisations of the Mass Transference Principle”, arXiv:2306.15535 (2023).

Additional references

3 papers in this index state this conjecture (2008–2023). The statement above is taken from the most recent of them; the others are arXiv:1704.06628, arXiv:0811.1234.

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