Luchka, A. Y., and O. B. Nesterenko. “Methods for the Solution of Boundary-Value Problems for Weakly Nonlinear Integro-Differential Equations With Parameters and Restrictions”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 61, no. 5, May 2009, pp. 672-9, https://umj.imath.kiev.ua/index.php/umj/article/view/3049.