AMERI, R.; BORZOOEI, R.A.; MOHAMMADZADEH, E. ENGEL FUZZY SUBGROUPS. Italian Journal of Pure and Applied Mathematics, [S. l.], v. 34, p. 251–262, 2015. Disponível em: https://journals.uniurb.it/index.php/ijpam/article/view/6357. Acesso em: 7 aug. 2026.