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FKS Problem 2 in dimension three

Dishant Shah

Palomar Registrypalomar/PALOMAR-2026-09-30-000026Sep 30, 2026math.COscore 0

A Lean-checked proof of the d = 3 case of FKS Problem 2: for every simple graph G on seven vertices, G or its complement has an injective placement in Euclidean three-space under which every edge has length 1. Non-edges are unconstrained and may also have length 1. The full question, for graphs on 2d + 1 vertices in dimension d, is stated and marked open. In the notation of Alon and Kupavskii, the proved case gives f_D(7) ≤ 3; together with the published lower bound it implies f_D(7) = 3. The formal target is the seven-vertex disjunction, not a definition or equality for f_D. The research…

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