SKOLEM, Th. A Set Theory Based on a Certain 3-Valued Logic. Mathematica Scandinavica, Berkeley, CA, United States, v. 8, p. 127–136, 1960. DOI: 10.7146/math.scand.a-10600. Disponível em: https://journals.msp.org/mscand/article/view/2745. Acesso em: 25 jul. 2026.