Chromatic symmetric functions of claw-free graphs are not Schur positive

Jacob P. Matherne, Alejandro H. Morales

Matherne and Morales give a 12-vertex, 19-edge bipartite graph G3 whose chromatic symmetric function is reported Schur positive while its three-variable specialization omits lattice-point weight (7,4,1) between present weights (6,6,0) and (8,2,2).

Sources for this record

What was already known

Monical conjectured Schur positivity always implied a saturated Newton polytope for every finite-variable specialization. Prior work placed a counterexample at at least 12 vertices.

AI involvement AI-centered

ChatGPT-5.6 Sol Pro found G3 in Matherne’s first prompt. Matherne and Morales selected the question, interpreted the graph and supplied the mathematical argument.

The model found the decisive graph G3 in a human-chosen search problem.

Importance Notable

If the reported Schur positivity is confirmed for G3, this explicit graph refutes the universal conjecture.

Limitations

The color-class obstruction is explained, but the displayed Schur expansion is labeled G2 although the surrounding argument concerns G3. The exact positivity certificate needs clarification.

Technical verification Partial

The paper supplies an elementary color-class proof of the missing SNP weight and reports exact SageMath calculation of Schur positivity. The displayed expansion is labeled G2, a graph §2 says is Schur negative, so the exact G3 positivity certificate needs clarification before complete verification. The written proof alone is not a separate documented human check.

Formal checking

Exact symbolic Schur expansion linked from Example 3.1; displayed label conflict

Checker
Matherne and Morales using SageMath
Scope
Reported Schur positivity of G3
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Full

The authors explain the G3 graph, coloring obstruction and logical counterexample mechanism.

Correction and publication history

2026-10-18 · publication

If the reported Schur positivity is confirmed for G3, this explicit graph refutes the universal conjecture.

Read this published revision