BUTZ, C.; JOHNSTONE, P. T. Classifying Toposes for First Order Theories. BRICS Report Series, [S. l.], v. 4, n. 20, 1997. DOI: 10.7146/brics.v4i20.18946. Disponível em: https://tidsskrift.dk/brics/article/view/18946. Acesso em: 28 mar. 2024.