KopachevskiiN. D., and SemkinaE. V. “Complete Volterra Integrodifferential Equations of the Second Order Unsolved With Respect to the Higher Derivative”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 66, no. 11, Nov. 2014, pp. 1485-97, https://umj.imath.kiev.ua/index.php/umj/article/view/2240.