An upper bound of 61 for the Ramsey number R(3,3,3,3)

Milos Tatarevic

Tatarevic reports that every four-colouring of the edges of K₆₁ contains a monochromatic triangle, lowering the upper bound for R(3,3,3,3) from 62 to 61. The argument combines incidence counting, finite neighbourhood classifications and 56,723 SAT exclusions.

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What was already known

Fettes, Kramer and Radziszowski proved the upper bound 62 in 2004. The 2026 Small Ramsey Numbers survey gives 51≤R(3,3,3,3)≤62. The new claim improves the upper endpoint by one, without determining the exact number.

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AI involvement

Section 7 assigns the A/B/D reductions to GPT-5.6 and Fable, and the C reduction, integration and simplified compatibility argument to GPT-6 Astra. Tatarevic directed the research and computations. These specified mathematical reductions support AI-centered inclusion, beyond code generation alone.

Importance

A concrete improvement to a longstanding finite Ramsey bound, with a detailed reduction and reproducible computational record.

Limitations

Lean checks the reductions, finite classifications and input-generation correspondence, but its final theorem assumes that all 56,723 formulas are unsatisfiable. Two SAT solvers reported UNSAT on every generated input; these exclusions are not checked by Lean in this artifact. The exact Ramsey number and a stronger lower bound remain unresolved.

Technical verification

Correction and publication history

2026-10-28 · amendment

Lists the original paper once while retaining the specific checking and provenance references. Research claims and rating levels are unchanged.

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2026-10-28 · amendment

Clarifies that the source reports completed checking but does not supply its exact completion date. Research claims and rating levels are unchanged.

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2026-10-28 · publication

Newly reviewed source-backed research contribution with contribution-specific AI attribution and checking limits.

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