The Kaufman exceptional set conjecture for planar projections

Let KR2K\subset\mathbb{R}^{2} be a Borel set, and let πe ⁣:R2R\pi_e\colon\mathbb{R}^{2}\to\mathbb{R} be the orthogonal projection πe(x)=xe\pi_e(x)=x\cdot e for eS1e\in S^{1}. Assume that 0t/2st10\leq t/2\leq s\leq t\leq 1 and dimHKt\dim_{\mathrm{H}}K\geq t. Kaufman's exceptional set conjecture.

dimH{eS1:dimHπe(K)<s}2st.\dim_{\mathrm{H}}\{e\in S^{1}:\dim_{\mathrm{H}}\pi_e(K)<s\}\leq 2s-t.

This conjecture would improve Kaufman's bound for the exceptional directions when the set has Hausdorff dimension at least t>st>s. The bound is known to be sharp, but the general conjecture remains open.

Sources & referencesView supporting material

Primary source

Tuomas Orponen, “Improving Kaufman's exceptional set estimate for packing dimension”, arXiv:1610.06745 (2016).

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