The Ehrhart–Zeta duality conjecture for linear arbors

Let tt be a linear arbor, meaning an arbor in which each vertex has at most one sub-tree. Let Rev(t)\operatorname{Rev}(t) be its reverse, obtained by putting the vertices in the opposite order. Let QtQ_t be the associated polytope, Et(u)E_t(u) its Ehrhart polynomial, and PtP_t its associated poset with Zeta polynomial Zt(u)Z_t(u).

The Ehrhart–Zeta duality conjecture. For every linear arbor tt,

Et(u)=ZRev(t)(u+1).E_t(u)=Z_{\operatorname{Rev}(t)}(u+1).

The conjecture would identify the normalized volume of QtQ_t with the number of maximal chains of PRev(t)P_{\operatorname{Rev}(t)}. The source presents this as open and notes a further expected h-vector symmetry under reversal.

Sources & referencesView supporting material

Primary source

Frédéric Chapoton, “On posets and polytopes attached to arbors”, arXiv:2503.04247 (2025).

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