Sun, Longfa, and Yunbai Dong. “More on Stability of Two Functional Equations”. Ukrains’kyi Matematychnyi Zhurnal 75, no. 6 (June 20, 2023): 859 - 868. Accessed December 26, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/7121.