Argyros, I. K. “An Error Analysis for the Steffensen Method under Generalized Zabrejko-Ngyen-Type Assumptions”. Rev. Anal. Numér. Théor. Approx., vol. 25, no. 1, Aug. 1996, pp. 11-22, https://ictp.acad.ro/jnaat/journal/article/view/1996-vol25-nos1-2-art2.