JONDRUP, S. Flat and projective modules. MATHEMATICA SCANDINAVICA, [S. l.], v. 43, p. 336–342, 1978. DOI: 10.7146/math.scand.a-11787. Disponível em: https://www.mscand.dk/article/view/11787. Acesso em: 4 may. 2024.