Oberlin's restricted projection conjecture in three dimensions

Let t[0,3]t\in[0,3] and let s[0,min{t,1}]s\in\left[0,\min\{t,1\}\right]. For a Borel set AR3A\subseteq\mathbb{R}^3 with dimA=t\dim A=t, write ρθ(A)\rho_\theta(A) for its restricted projection at angle θ[0,2π)\theta\in[0,2\pi). Oberlin's restricted projection conjecture. One should have

dim{θ[0,2π):dimρθ(A)<s}max{3s2t2,0}.\dim\left\{\theta\in[0,2\pi):\dim\rho_\theta(A)<s\right\}\leq\max\left\{\frac{3s}{2}-\frac{t}{2},0\right\}.

The conjecture is an analogue of Oberlin's planar projection conjecture for restricted projections in R3\mathbb{R}^3. It is known when t1t\leq1 and s=ts=t, and when t1t\geq1 and s=1s=1; the case s=t/3s=t/3 is the paper's preceding proposition. The intermediate cases remain open.

Sources & referencesView supporting material

Primary source

John Green, Terence L. J. Harris, Yumeng Ou, Kevin Ren and Sarah Tammen, “Incidence bounds related to circular Furstenberg sets”, arXiv:2502.10686 (2025).

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