ULLRICH, D. A general principle for purely model-theoretical proofs of Gödel’s second incompleteness theorem. Logic and Logical Philosophy, [S. l.], v. 6, n. 6, p. 173–185, 1998. DOI: 10.12775/LLP.1998.009. Disponível em: https://apcz.umk.pl/LLP/article/view/LLP.1998.009. Acesso em: 25 jul. 2024.