RUAS, Maria Aparecida Soares. On the degree of $C^l$-determinacy. Mathematica Scandinavica, Berkeley, CA, United States, v. 59, p. 59–70, 1986. DOI: 10.7146/math.scand.a-12154. Disponível em: https://journals.msp.org/mscand/article/view/1518. Acesso em: 25 jul. 2026.