Velani's dyadic approximation conjecture for the middle-third Cantor set

From papers

Let ψ:NR+\psi:{\mathbb{N}}\to{\mathbb{R}}^+ be monotonic, and let

W2(ψ)={x[0,1]:xpq<ψ(q)q for infinitely many (p,q)Z×A(2)},W_2(\psi)=\left\{x\in[0,1]:\left|x-\frac{p}{q}\right|<\frac{\psi(q)}{q}\text{ for infinitely many }(p,q)\in{\mathbb{Z}}\times\mathcal A(2)\right\},

where A(2)={2n:n=0,1,2,}\mathcal A(2)=\{2^n:n=0,1,2,\ldots\} and μ\mu denotes Lebesgue measure. Velani's conjecture.

μ(W2(ψ))={0if n=1ψ(2n)<,1if n=1ψ(2n)=.\mu(W_2(\psi))=\begin{cases}0&\text{if }\displaystyle\sum_{n=1}^{\infty}\psi(2^n)<\infty,\\[4pt]1&\text{if }\displaystyle\sum_{n=1}^{\infty}\psi(2^n)=\infty. \end{cases}

This is the expected zero--one law for dyadic rational approximation in the middle-third Cantor set, analogous to the known triadic result. The source describes it as an expected eventual truth and notes that the present work supports it; no resolution is supplied here.

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Sources & referencesView supporting material

Primary source

Demi Allen, Sam Chow and Han Yu, “Dyadic Approximation in the Middle-Third Cantor Set”, arXiv:2005.09300 (2020).

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