Zernov, A. E. “On the Solvability and Asymptotics of Solutions of One Functional Differential Equation With Singularity”. Ukrains’kyi Matematychnyi Zhurnal, vol. 53, no. 4, Apr. 2001, pp. 455-6, https://umj.imath.kiev.ua/index.php/umj/article/view/4268.