POTRA, F. -a.; PTÁK, Vlastimil. Nondiscrete induction and double step secant method. MATHEMATICA SCANDINAVICA, [S. l.], v. 46, p. 236–250, 1980. DOI: 10.7146/math.scand.a-11866. Disponível em: https://www.mscand.dk/article/view/11866. Acesso em: 5 dec. 2025.