The CTI–Schröder polynomial equality conjecture

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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)=∑w∈Schro¨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.

References

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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