References
- J. Aczél and E. Vincze, Über eine gemeinsame Verallgemeinerung zweier Funktionalgleichungen von Jensen, Publ. Math. Debrecen 10 (1963), 326–344.
- Y. Aissi, D. Zeglami, and A. Mouzoun, A quadratic functional equation with involutive automorphisms on semigroups, Bol. Soc. Mat. Mex. (3) 28 (2022), no. 1, Paper No. 19, 13 pp.
- A. Akkaoui, B. Fadli, and M. El Fatini, The Drygas functional equation on abelian semigroups with endomorphisms, Results Math. 76 (2021), no. 1, Paper No. 42, 13 pp.
- B. Fadli, D. Zeglami, and S. Kabbaj, A variant of the quadratic functional equation on semigroups, Proyecciones 37 (2018), no. 1, 45–55.
- Pl. Kannappan, On inner product spaces. I, Math. Japon. 45 (1997), no. 2, 289–296.
- Pl. Kannappan, On quadratic functional equation, Int. J. Math. Stat. Sci. 9 (2000), no. 1, 35–60.
- Pl. Kannappan, Functional Equations and Inequalities with Applications, Springer Monogr. Math., Springer, New York, 2009.
- M. Kuczma, Functional Equations in a Single Variable, Monografie Mat., 46, Polish Scientific Publishers, Warsaw, 1968.
- M. Kuczma, B. Choczewski, and R. Ger, Iterative Functional Equations, Encyclopedia Math. Appl., 32, Cambridge University Press, Cambridge, 1990.
- S. Kurepa, On the quadratic functional, Acad. Serbe Sci. Publ. Inst. Math. 13 (1959), 57–72.
- Kh. Sabour, A variant of Drygas’ functional equation with an endomorphism, Asia Math. 4 (2020), no. 1, 63–68.
- Kh. Sabour and S. Kabbaj, Jensen’s and the quadratic functional equations with an endomorphism, Proyecciones 36 (2017), no. 1, 187–194.
- P. Sinopoulos, Functional equations on semigroups, Aequationes Math. 59 (2000), no. 3, 255–261.
- H. Stetkær, Functional equations on abelian groups with involution, Aequationes Math. 54 (1997), no. 1–2, 144–172.
- H. Stetkær, Functional Equations on Groups, World Scientific Publishing Co. Pte. Ltd., Singapore, 2013.
- D. Yang, The quadratic functional equation on groups, Publ. Math. Debrecen 66 (2005), no. 3–4, 327–348.