Ronto, M. I., A. M. Samoilenko, and S. I. Trofimchuk. “The Theory of the Numerical-Analytic Method: Achievements and New Trends of Development. V”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 5, May 1999, pp. 663–673, https://umj.imath.kiev.ua/index.php/umj/article/view/4652.