1. Abramovich S., Jameson G., Sinnamon G., Refining of Jensen’s inequality, Bull. Math. Soc. Sci. Math. Roumanie 47(95) (2004), 3–14.
2. Abramovich S., Jameson G., Sinnamon G., Inequalities for averages of convex and superquadratic functions, JIPAM, J. Inequal. Pure Appl. Math. 5 (2004), Art. 91.
3. Badora R., Przebieracz B., Volkmann P., Stability of the Pexider functional equation, Annales Mathematicae Silesianae 24 (2010), 7–13.
4. Balaj M., Wąsowicz Sz., Haar spaces and polynomial selections, Math. Pannon. 14 (2003), no. 1, 63–70.
5. Baron K., Matkowski J., Nikodem K., A sandwich with convexity, Math. Pannon. 5 (1994), no. 1, 139–144.
6. Bessenyei M., Páles Zs., Separation by linear interpolation families, J. Nonlinear Conv. Anal. 13 (2012), no. 1, 49–56.
7. Boros Z., Páles Zs., ℚ-subdifferential of Jensen-convex functions, J. Math. Anal. Appl. 321 (2006), 99–113.
8. Cabello Sánchez F., Castillo J.M.F., Uniform boundedness and twisted sums of Banach spaces, Houston J. Math. 30 (2004), 523–536.
9. Charifi A., Bouikhalene B., Elqorachi E., Hyers–Ulam–Rassias stability of a generalized Pexider functional equation, Banach. J. Math. Anal. 1 (2007), no. 2, 176–185.
10. Ž. Djoković D., A representation theorem for (X_1-1)(X_2-1)...(X_n-1) and its applications, Ann. Polon. Math. 22 (1969), 189–198.
11. Gajda Z., A generalization of D’Alembert’s Functional Equation, Funkc. Ekvacioj 33 (1990), 69–77.
12. Hooshmand M.H., Haili H.K., Decomposer and associative functional equations, Indag. Mathem. 18 (2007), no. 4, 539–554.
13. Kaluszka M., Krzeszowiec M., Pricing insurance contracts under Cumulative Prospect Theory, Insurance: Mathematics and Economics 50 (2012), 159–166.
14. Kominek Z., Troczka K., Some remarks on subquadratic functions, Demonstratio Math. 39 (2006), 751–758.
15. Maksa Gy., Páles Zs., The equality case in some recent convexity inequalities, Opuscula Math. 31 (2011), no. 2, 269–277.
16. Matkowski J., A generalization of the Gołąb–Schinzel functional equation, Aequationes Math. 80 (2010), 181–192.
17. Mazur S., Orlicz W., Grundlegende Eigenschaften der Polynomischen Operationen I.–II., Studia Math. 5 (1934), 50–68 & 179–189.
18. Nikodem K., Páles Zs., Generalized convexity and separation theorems, J. Convex Anal. 14 (2007), no. 2, 239–248.
19. Nikodem K., Wąsowicz Sz., A sandwich theorem and Hyers-Ulam stability of affine functions, Aequationes Math. 49 (1995), no. 1–2, 160–164.
20. Nikodem K., Pales Zs., Wąsowicz S., Abstract separation theorems of Rode type and their applications, Ann. Polon. Math. 72 (1999), 207–217.
21. Pearce E.M., Rubinov A.M., P-functions, quasi-convex functions and Hadamard-type inequalities, J. Math. Anal. Appl. 240 (1999), 92–104.
22. Rosenbaum R.A., Subadditive functions, Duke Math. J. 17 (1950), 227–242.
23. Sibaha M.A., Bouikhalene B., Elqorachi E., Hyers–Ulam–Rassias stability of the K-quadratic functional equation, J. Ineq. Pure and Appl. Math. 8 (2007), article 89.
24. Smajdor W., Subadditive and subquadratic set-valued functions, Scientific Publications of the University of Silesia, vol. 889, Katowice, 1987.
25. Stetkær H., Functional equation on abelian groups with involution II., Aequationes Math. 55 (1998), 227–240.
26. Stetkær H., Functional equations involving means of functions on the complex plane, Aequationes Math. 56 (1998), 47–62. Google Scholar