Al-Dababseh, A.F. (2001) “On τ-Closed Formations of n-Ary Group”, Ukrains’kyi Matematychnyi Zhurnal, 53(1), pp. 113–116. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4226 (Accessed: 5 December 2025).