Rassias JM, Xu TZ, Xu WX. A generalized mixed type of quartic, cubic, quadratic and additive functional equation. Ukr. Mat. Zhurn. [Internet]. 2011Mar.25 [cited 2024Nov.27];63(3):399-15. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/2725