Dimension lower-bound conjecture for sums of projected planar sets and sets on a line

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Let K1⊂R2K_{1}\subset\mathbb{R}^{2} and K2⊂RK_{2}\subset\mathbb{R} be analytic sets, with ℘θ(K1)\wp_{\theta}(K_{1}) denoting the projection of K1K_{1} in direction determined by θ\theta. Assume

dim⁡HK1+dim⁡HK2≤1.\dim_{\mathrm{H}}K_{1}+\dim_{\mathrm{H}}K_{2}\leq 1.

Projected-sum dimension conjecture. For almost every θ∈(0,2π)\theta\in(0,2\pi),

dim⁡H(℘θ(K1)+K2)≥dim⁡HK1+dim⁡HK2.\dim_{\mathrm{H}}\bigl(\wp_{\theta}(K_{1})+K_{2}\bigr)\geq \dim_{\mathrm{H}}K_{1}+\dim_{\mathrm{H}}K_{2}.

This is presented as a weaker variant of the paper's dimension-conservation conjecture. The preceding proposition proves a related lower bound for product sets and the special family of projections, but the stated projected-sum claim remains open in the supplied text.

References

Primary source

Katrin Fässler and Tuomas Orponen, “On restricted families of projections in R^3”, arXiv:1302.6550 (2014).

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