Pham, Thi Mai Tham, Thi Le Hang Vo, and Van Dung Nguyen. “On the Hyperstability of the Drygas Functional Equations”. Dong Thap University Journal of Science 10, no. 3 (June 14, 2021): 21–30. Accessed September 8, 2024. https://dthujs.vn/index.php/dthujs/article/view/144.