JONDRUP, S. Flat and projective modules. Mathematica Scandinavica, Berkeley, CA, United States, v. 43, p. 336–342, 1978. DOI: 10.7146/math.scand.a-11787. Disponível em: https://journals.msp.org/mscand/article/view/1860. Acesso em: 25 jul. 2026.