NICOLAU, Artur; SUÁREZ, Daniel. Approximation by invertible functions of $H^{\infty}$. Mathematica Scandinavica, Berkeley, CA, United States, v. 99, n. 2, p. 287–319, 2006. DOI: 10.7146/math.scand.a-15013. Disponível em: https://journals.msp.org/mscand/article/view/684. Acesso em: 24 jul. 2026.