Selezneva, N. V. “Mathematical Modeling of Nilpotent Subsemigroups of Semigroups of Contracting Transformations of a Boolean”. Ukrains’kyi Matematychnyi Zhurnal 61, no. 7 (July 25, 2009): 976-985. Accessed May 4, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3072.