MHEUBO-KWEGNA, Olivier A.; NGANOU, Jean B. INVERTIBLE ELEMENTS IN BCK-ALGEBRAS. Italian Journal of Pure and Applied Mathematics, [S. l.], v. 33, p. 81–92, 2014. Disponível em: https://journals.uniurb.it/index.php/ijpam/article/view/6271. Acesso em: 7 aug. 2026.