GRANIRER, E.; RAJAGOPALAN, M. A Note on the Radical of the Second Conjugate Algebra of a Semigroup Algebra. Mathematica Scandinavica, Berkeley, CA, United States, v. 15, p. 163–166, 1964. DOI: 10.7146/math.scand.a-10740. Disponível em: https://journals.msp.org/mscand/article/view/2608. Acesso em: 25 jul. 2026.