1. Aczél, J.: The general solution of two functional equations by reduction to functions additive in two variables and with aid of Hamel bases. Glasnik Mat.-Fiz. Astronom. Drustvo Mat. Fiz. Hrvatske 20, 65–73 (1965)
2. Aczél, J., Vincze, E.: Über eine gemeinsame Verallgemeinerung zweier Funktionalgleichungen von Jensen. Publ. Math. Debr. 10, 326–344 (1963)
3. Belaid, B., Elhoucien, E., Ahmed, R.: Hyers–Ulam stability of the generalized quadratic functional equation in amenable semigroups. J. Inequal. Pure Appl. Math. 8, 18 (2007)
4. Chung, J.K., Ebanks, B.R., Ng, C.T., Sahoo, P.K.: On a quadratic-trigonometric functional equation and some applications. Trans Am. Math. Soc. 347, 1131–1161 (1995)
5. Chung, J.K., Kannappan, Pl., Ng, C.T., Sahoo, P.K.: Measures of distance between probability distributions. J. Math. Anal. Appl. 139, 280–292 (1989)