Two-line intersection conjecture for rich-line-free point sets

Let PR2P\subseteq\mathbb{R}^2 be a finite point set. For a line ll, let L(P)lL(P)\cap l denote the set of points where lines from L(P)L(P) intersect ll. Assume that no more than P1δ|P|^{1-\delta} points of PP lie on any line, and let l1l_1 and l2l_2 be distinct arbitrary lines. For every δ>0\delta>0 there exists ϵ=ϵ(δ)>0\epsilon=\epsilon(\delta)>0 such that

L(P)l1+L(P)l2P1+ϵ.|L(P)\cap l_1|+|L(P)\cap l_2|\gg |P|^{1+\epsilon}.

Two-line intersection conjecture. For all δ>0\delta>0, there exists ϵ=ϵ(δ)>0\epsilon=\epsilon(\delta)>0 for which the displayed bound holds for every such PP, l1l_1, and l2l_2. This conjecture predicts a sum-product-type expansion for intersections of the line set with two distinct lines, once very rich lines in PP are excluded; its status is open in the supplied source.

Sources & referencesView supporting material

Primary source

Oliver Roche-Newton and Audie Warren, “New Expander Bounds from Affine Group Energy”, arXiv:1905.03701 (2019).

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