LEVIN, Gerson. Finitely generated Ext algebras. Mathematica Scandinavica, Berkeley, CA, United States, v. 49, p. 161–180, 1981. DOI: 10.7146/math.scand.a-11929. Disponível em: https://journals.msp.org/mscand/article/view/1739. Acesso em: 25 jul. 2026.