ELLENTUCK, E. On the Degrees of Universal Regressive Isols. MATHEMATICA SCANDINAVICA, [S. l.], v. 32, p. 145–164, 1973. DOI: 10.7146/math.scand.a-11451. Disponível em: https://www.mscand.dk/article/view/11451. Acesso em: 1 may. 2024.