Zernov, A. E. “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, Vol. 53, no. 2, Feb. 2001, pp. 258-62, https://umj.imath.kiev.ua/index.php/umj/article/view/4243.