CHRISTENSEN, D. J.; PIERCE, R. S. Free Products of $\alpha$-Distributive Boolean Algebras. MATHEMATICA SCANDINAVICA, [S. l.], v. 7, p. 81–105, 1959. DOI: 10.7146/math.scand.a-10564. Disponível em: https://tidsskrift.dk/math/article/view/10564. Acesso em: 14 aug. 2026.