Phillipson, Mitch, Catherine H. Yan, and Jean Yeh. “Chains of Length 2 in Fillings of Layer Polyominoes”. The Electronic Journal of Combinatorics 20, no. 3 (September 26, 2013): P51. Accessed March 15, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v20i3p51.