Derech, V. D. “On Permutable Congruences on Antigroups of Finite Rank”. Ukrains’kyi Matematychnyi Zhurnal 56, no. 3 (March 25, 2004): 346–351. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3758.