Bousquet-Mélou, Mireille. “Four Classes of Pattern-Avoiding Permutations Under One Roof: Generating Trees With Two Labels”. The Electronic Journal of Combinatorics 9, no. 2 (November 7, 2003): #R19. Accessed April 19, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v9i2r19.