Y. V. Gorbatenko, “Existence and uniqueness of mild solutions of second order semilinear differential equations in Banach space”, MFAT, vol. 17, no. 1, pp. 1–9, Mar. 2011, Accessed: Feb. 04, 2026. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/465