OLIN, P. Free products and elementary types of Boolean Algebras. MATHEMATICA SCANDINAVICA, [S. l.], v. 38, p. 5–23, 1976. DOI: 10.7146/math.scand.a-11612. Disponível em: https://www.mscand.dk/article/view/11612. Acesso em: 27 apr. 2024.