GOODSTEIN, R. L. Models of Propositional Calculi in Recursive Arithmetic. MATHEMATICA SCANDINAVICA, [S. l.], v. 6, p. 293–296, 1958. DOI: 10.7146/math.scand.a-10554. Disponível em: https://www.mscand.dk/article/view/10554. Acesso em: 6 may. 2024.