ClosedComputer Science Ai
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Smaller 5-chromatic unit-distance graphs are found by SAT with symmetry breaking. Solver-dominated; retired as a selection error on our part.
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An explicit unit-distance graph with at most 508 vertices and chromatic number 5, including exact coordinates or an algebraic construction and a machine-checkable certificate of non-4-colourability. The verifier must independently check every unit-distance edge and the colouring lower bound.
The smallest known 5-chromatic unit-distance graph has 509 vertices, while the chromatic number of the plane remains in {5,6,7}. A smaller graph is a distinct, crisp construction target and does not overlap with the separate bounty for narrowing the global interval. Source: https://mathworld.wolfram.com/Hadwiger-NelsonProblem.html
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Opened Jul 28, 2026 · closed Aug 11, 2026