SJÖDIN, G. A set of generators for $\mathrm{Ext}_R(k,k)$. MATHEMATICA SCANDINAVICA, [S. l.], v. 38, p. 199–210, 1976. DOI: 10.7146/math.scand.a-11629. Disponível em: https://www.mscand.dk/article/view/11629. Acesso em: 3 may. 2024.