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

Jacob P. Matherne, Alejandro H. Morales

Matherne and Morales give two 12-vertex claw-free line graphs whose chromatic symmetric functions have [s₃₃₃₃] coefficients −64 and −40. Either graph refutes Stanley’s claim that every claw-free graph is Schur-positive.

Sources for this record

What was already known

The 1995 conjecture was known for co-bipartite graphs and claw-free incomparability graphs. Prajapati found independent counterexamples at about the same time.

AI involvement AI-centered

Morales asked ChatGPT 5.6 Sol Pro to search; its second attempt found the two graphs using SAT solvers. Matherne and Morales identified their line-graph structure and computed the exact coefficients.

The model found the retained counterexample graphs within a human-chosen search target.

Importance Notable

The explicit graphs settle the universal conjecture, while contemporaneous human examples limit any sole priority claim.

Limitations

The exact coefficients are reported from SageMath computations. Later infinite counterexample families are separate human work.

Technical verification Formal (exact SageMath symbolic computation)

The finite graph condition follows from line-graph construction and the authors report exact SageMath Schur coefficients for both graphs. This is a source-reported exact computational check, not a locally reproduced run.

Formal checking

Exact finite symbolic coefficient computation plus line-graph construction

Checker
Matherne and Morales using SageMath
Scope
G1 and G2 have [s_3333] coefficients −64 and −40; both are line graphs and claw-free
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 graphs, coefficient counterexample and relation to known positive graph classes.

Correction and publication history

2026-10-18 · publication

The explicit graphs settle the universal conjecture, while contemporaneous human examples limit any sole priority claim.

Read this published revision