Psi-expansion conjecture for interval graphs

Let G=([n],E)G=([n],E) be an interval graph. For a composition αn\alpha\vDash n, let Ψα\Psi_\alpha be the type 1 power sum quasisymmetric function, let zα=zλ(α)z_\alpha=z_{\lambda(\alpha)}, and let NG,α\mathcal{N}_{G,\alpha} be the set of permutations defined by requiring that each segment of composition shape α\alpha has neither a GG-descent nor a nontrivial left-to-right GG-maximum. Let ω\omega be the involution on QSym\operatorname{QSym}. First conjecture.

ωχG[X;q]=αnΨαzασNG,αqinv~G(σ).\omega \chi_G[X;q]=\sum_{\alpha\vDash n}\frac{\Psi_\alpha}{z_{\alpha}}\sum_{\sigma \in \mathcal{N}_{G,\alpha}}q^{\widetilde{\mathsf{inv}}_G(\sigma)}.

This extends the power-sum expansion known for Dyck graphs and proposes a quasisymmetric analogue for interval graphs.

Sources & referencesView supporting material

Primary source

Michele D'Adderio, Roberto Riccardi and Viola Siconolfi, “Chromatic functions, interval orders and increasing forests”, arXiv:2311.09685 (2023).

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