GOODSTEIN, R. L. Logic-free formalisations of recursive arithmetic. MATHEMATICA SCANDINAVICA, [S. l.], v. 2, p. 246–260, 1954. DOI: 10.7146/math.scand.a-10412. Disponível em: https://www.mscand.dk/article/view/10412. Acesso em: 14 apr. 2025.