Kaplun, Y. I., & Samoilenko, V. G. (2001). Existence and Extendability of Solutions of the Equation $g(t, x) = 0$. Ukrains’kyi Matematychnyi Zhurnal, 53(3), 372-382. https://umj.imath.kiev.ua/index.php/umj/article/view/4259