Ronto, M. I., A. M. Samoilenko, and S. I. Trofimchuk. 1999. “The Theory of the Numerical-Analytic Method: Achievements and New Trends of Development. VI”. Ukrains’kyi Matematychnyi Zhurnal 51 (7): 960–971. https://umj.imath.kiev.ua/index.php/umj/article/view/4685.