English

Decorated square paths at q=-1

Combinatorics 2024-08-21 v1

Abstract

The valley Delta square conjecture states that the symmetric function [nk]q[n]qΔenkω(pn)\frac{[n-k]_q}{[n]_q}\Delta_{e_{n-k}}\omega(p_n) can be expressed as the enumerator of a certain class of decorated square paths with respect to the bistatistic (dinv,area). Inspired by recent positivity results of Corteel, Josuat-Verg\`{e}s, and Vanden Wyngaerd, we study the evaluation of this enumerator at q=1q=-1. By considering a cyclic group action on the decorated square paths which we call cutting and pasting, we show that [nk]q[n]qΔenkω(pn),h1nq=1\left.\left\langle \frac{[n-k]_q}{[n]_q}\Delta_{e_{n-k}}\omega(p_n), h_1^n\right\rangle\right|_{q=-1} is 00 whenever nkn-k is even, and is a positive polynomial related to the Euler numbers when nkn-k is odd. We also show that the combinatorics of this enumerator is closely connected to that of the Dyck path enumerator for Δenk1en,h1n\langle\Delta_{e_{n-k-1}}'e_n,h_1^n\rangle considered by Corteel-Josuat Verg\`{e}s-Vanden Wyngaerd.

Keywords

Cite

@article{arxiv.2408.10640,
  title  = {Decorated square paths at q=-1},
  author = {Sylvie Corteel and Alexander Lazar and Anna Vanden Wyngaerd},
  journal= {arXiv preprint arXiv:2408.10640},
  year   = {2024}
}
R2 v1 2026-06-28T18:17:49.895Z