SJÖDIN, Gunnar. A set of generators for $\mathrm{Ext}_R(k,k)$. Mathematica Scandinavica, Berkeley, CA, United States, v. 38, p. 199–210, 1976. DOI: 10.7146/math.scand.a-11629. Disponível em: https://journals.msp.org/mscand/article/view/2017. Acesso em: 25 jul. 2026.