Quantitative Besicovitch projection conjecture for AD-regular planar sets

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Let s∈(0,1)s\in (0,1) and C0∈(1,∞)C_0\in (1,\infty). Let E⊂R2E\subset \mathbb{R}^2 be a bounded AD-regular set with constant C0C_0, meaning that EE is closed and, for every x∈Ex\in E and 0<r<diam⁡(E)0<r<\operatorname{diam}(E),

C0−1r≤H1(E∩B(x,r))≤C0r.C_0^{-1}r\leq\mathcal{H}^1(E\cap B(x,r))\leq C_0r.

Write Fav⁡(E)\operatorname{Fav}(E) for the Favard length of EE, and let Lip⁡(Γ)\operatorname{Lip}(\Gamma) denote the Lipschitz constant of a Lipschitz graph Γ\Gamma. Quantitative Besicovitch projection conjecture. If

Fav⁡(E)≥sdiam⁡(E),\operatorname{Fav}(E)\geq s\operatorname{diam}(E),

then there exists a Lipschitz graph Γ⊂R2\Gamma\subset\mathbb{R}^2 such that

Lip⁡(Γ)≲s,C01\operatorname{Lip}(\Gamma)\lesssim_{s,C_0}1

and

H1(Γ∩E)≳s,C0H1(E).\mathcal{H}^1(\Gamma\cap E)\gtrsim_{s,C_0}\mathcal{H}^1(E).

This would provide a quantitative counterpart to Besicovitch's qualitative projection theorem, with both the Lipschitz constant and the length of the intersection controlled in terms of ss and C0C_0. The statement is presented as a conjectural quantitative result in the source, and its resolution is not supplied here.

References

Primary source

Damian Dąbrowski, “Quantitative Besicovitch projection theorem for irregular sets of directions”, arXiv:2211.16911 (2025).

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