Y. I. Bigun, “Existence, uniqueness, and dependence on a parameter of solutions of differential-functional equations with ordinary and partial derivatives”, Ukr. Mat. Zhurn., vol. 49, no. 5, pp. 715–719, May 1997, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5053