Dudek, Andrzej, Jarosław Grytczuk, and Andrzej Ruciński. “Variations on Twins in Permutations”. The Electronic Journal of Combinatorics 28, no. 3 (July 16, 2021): #P3.19. Accessed May 27, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v28i3p19.