NorkinB. V. “On the Solution of the Basic Integral Equation of Actuarial Mathematics by the Method of Successive Approximations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, no. 12, Dec. 2007, pp. 1689–1698, https://umj.imath.kiev.ua/index.php/umj/article/view/3422.