The CTI–Schröder polynomial equality conjecture

Let Sn,dS_{n,d} be the complete split graph, let Fn,dCTI(q,t)\mathfrak{F}_{n,d}^{CTI}(q,t) be the q,tq,t-CTI polynomial, and let Schro¨dern,d\mathsf{Schr\ddot{o}der}_{n,d} be the set of (n,d)(n,d)-Schröder paths with statistics area\mathsf{area} and bounceSch\mathsf{bounce}^{\mathsf{Sch}}. CTI–Schröder equality conjecture.

Fn,dCTI(q,t)=wSchro¨dern,dqarea(w)tbounceSch(w).\mathfrak{F}_{n,d}^{CTI}(q,t)=\sum_{w\in\mathsf{Schr\ddot{o}der}_{n,d}}q^{\mathsf{area}(w)}t^{\mathsf{bounce}^{\mathsf{Sch}}(w)}.

This is equivalent to the CTI–ITC equality conjecture because the paper proves equality of the q,tq,t-Schröder and q,tq,t-ITC polynomials. The general equality remains open, although special cases are established.

Sources & referencesView supporting material

Primary source

Henri Derycke, Mark Dukes and Yvan Le Borgne, “The sandpile model on the complete split graph: q,t-Schröder polynomials, sawtooth polyominoes, and a cycle lemma”, arXiv:2402.15372 (2025).

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