ELLENTUCK, Erik. 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://tidsskrift.dk/math/article/view/11451. Acesso em: 13 aug. 2026.