Lin, Zhicong. “Proof of Gessel’s $\gamma$-Positivity Conjecture”. The Electronic Journal of Combinatorics 23, no. 3 (July 22, 2016): P3.15. Accessed April 3, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v23i3p15.