MACEDOŃSKA, O.; ŻABKA, M. On equivalence of semigroup identities. Mathematica Scandinavica, Berkeley, CA, United States, v. 88, n. 2, p. 161–181, 2001. DOI: 10.7146/math.scand.a-14321. Disponível em: https://journals.msp.org/mscand/article/view/884. Acesso em: 24 jul. 2026.