ERNSTRÖM, L. The spectrum associated to a radical operation. MATHEMATICA SCANDINAVICA, [S. l.], v. 73, p. 5–14, 1993. DOI: 10.7146/math.scand.a-12451. Disponível em: https://www.mscand.dk/article/view/12451. Acesso em: 3 may. 2024.