Korol’, I. I., and N. A. Perestyuk. “Once Again on the Samoilenko Numerical-Analytic Method of Successive Periodic Approximations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, no. 4, Apr. 2006, pp. 472–488, https://umj.imath.kiev.ua/index.php/umj/article/view/3468.