ERIKSSON, F. The Relation Between Two Generalisations of the Notion "Surface of Curvature $\leqq K$". MATHEMATICA SCANDINAVICA, [S. l.], v. 8, p. 339–355, 1960. DOI: 10.7146/math.scand.a-10616. Disponível em: https://www.mscand.dk/article/view/10616. Acesso em: 7 may. 2024.