BARBACK, J. Extensions to Regressive Isols. MATHEMATICA SCANDINAVICA, [S. l.], v. 25, p. 159–177, 1969. DOI: 10.7146/math.scand.a-10953. Disponível em: https://www.mscand.dk/article/view/10953. Acesso em: 29 apr. 2024.