ENGENES, H. Subobject Classifiers and Classes of Subfunctors. MATHEMATICA SCANDINAVICA, [S. l.], v. 34, p. 145–152, 1974. DOI: 10.7146/math.scand.a-11515. Disponível em: https://www.mscand.dk/article/view/11515. Acesso em: 3 may. 2024.