Open Research Index

Erdős 958: planar point sets with distance multiplicities {1, ..., n - 1}

Linmiao Xu

Palomar Registrypalomar/PALOMAR-2026-10-05-000004Oct 5, 2026math.COscore 0

A complete Lean 4 proof of the negative answer to Erdős problem 958: for every n ≥ 4, there exists an n-point configuration in the Euclidean plane determining n - 1 distinct interpoint distances with multiplicities {1, 2, ..., n - 1} that is neither equidistant on a line nor equidistant on a circle. Formalizing the May 2025 construction of Clemen, Dumitrescu, and Liu, the proof places n - 1 equally spaced points on a short arc of the unit circle together with the center (0, 0), uses strict monotonicity of chord lengths on [0, π/3) to compute the exact distance-multiplicity profile, and…

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