MACEDOŃSKA, O.; ŻABKA, M. On equivalence of semigroup identities. MATHEMATICA SCANDINAVICA, [S. l.], v. 88, n. 2, p. 161–181, 2001. DOI: 10.7146/math.scand.a-14321. Disponível em: https://www.mscand.dk/article/view/14321. Acesso em: 11 apr. 2025.