SJÖDIN, Gunnar. 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://tidsskrift.dk/math/article/view/11629. Acesso em: 14 aug. 2026.