Dukes M, Selig T, Smith JP, Steingrímsson E. Permutation Graphs and the Abelian Sandpile Model, Tiered Trees and Non-Ambiguous Binary Trees. Electron. J. Combin. [Internet]. 2019Aug.16 [cited 2026Apr.2];26(3):P3.29. Available from: https://www.combinatorics.org/ojs/index.php/eljc/article/view/v26i3p29