GHEISARI, Yousof; AHMAD, Abd Ghafur. Diagram Groups over Union of Two Semigroup Presentations of Natural Numbers by Adding Relations. MATEMATIKA, [S. l.], v. 26, p. 153–156, 2010. DOI: 10.11113/matematika.v26.n.558. Disponível em: https://matematika.utm.my/index.php/matematika/article/view/558. Acesso em: 20 may. 2024.