Zernov, A. E. 2001. “On the Solution of a Singular Cauchy Problem for a First-Order Differential Equation Unsolved With Respect to the Derivative of an Unknown Function”. Ukrains’kyi Matematychnyi Zhurnal 53 (2), 258-62. https://umj.imath.kiev.ua/index.php/umj/article/view/4243.