POTRA, F. -a.; PTÁK, Vlastimil. Nondiscrete induction and double step secant method. Mathematica Scandinavica, Berkeley, CA, United States, v. 46, p. 236–250, 1980. DOI: 10.7146/math.scand.a-11866. Disponível em: https://journals.msp.org/mscand/article/view/1781. Acesso em: 25 jul. 2026.