Short proofs in combinatorics, probability and number theory II

Boris Alexeev, Moe Putterman, Mehtaab Sawhney, Mark Sellke, Gregory Valiant

For every m≥1, an explicit K₄-free graph on 20m+31 vertices is 4-chromatic and vertex-critical, while every cycle has at most ten chords. This refutes the proposed unbounded forced chord count under the stated local 3-colorability condition.

Sources for this record

What was already known

Voss, building on Larson, forced an odd cycle with at least two chords in every K₄-free 4-chromatic graph. Erdős asked whether stronger local 3-colorability conditions forced more chords.

AI involvement AI-led

An internal OpenAI model found the pentagon-block graph family and an original color-criticality proof. Alexeev, Putterman, Sawhney, Sellke and Valiant say they verified the model solution and replaced part of its proof with their stronger 2-degeneracy argument.

The model supplied the central graph family and original proof; task prompting is not documented finely enough for AI-autonomous.

Importance Notable

The bounded-chord family answers the specific Erdős graph-coloring question.

Limitations

The paper’s stronger proof that every proper subgraph is 2-degenerate is due to the human coauthors. No separate machine certificate for the family is documented.

Technical verification Formal (human)

The five human coauthors report that they verified the model’s graph solution before publication. Their later stronger degeneracy argument is credited to them.

Independent checking

human verification while digesting the proof; retained proof also uses their 2-degeneracy argument; §1, Comment on the use of AI; §4, Theorem 4.1 and Propositions 4.5–4.10

Checker
Alexeev, Putterman, Sawhney, Sellke and Valiant
Scope
Model's Problem 1091 graph family and original color-criticality solution
Basis
Reported by the linked checker
Evidence source

Human understanding Full

The authors explain the pentagon forcing and chord count and supplied the simpler stronger degeneracy route; this establishes understanding of the central construction.

Correction and publication history