ENGENES, Hans. Subobject Classifiers and Classes of Subfunctors. Mathematica Scandinavica, Berkeley, CA, United States, v. 34, p. 145–152, 1974. DOI: 10.7146/math.scand.a-11515. Disponível em: https://journals.msp.org/mscand/article/view/2132. Acesso em: 25 jul. 2026.