The additive approximation on a four-variate Jensen-type operator equation (Q1415173)

The problem of Ulam-Hyers-Rassias stability of Jensen-type functional equations is investigated. The author obtains classical results, applying the methods used by \textit{P. Gavruţa} [J. Math. Anal. Appl. 184, No. 3, 431--436 (1994; Zbl 0818.46043)], \textit{D. H. Hyers} [Proc. Natl. Acad. Sci. USA 27, 431--436 (1941; Zbl 0061.26403)] and \textit{Th. M. Rassias} [Proc. Am. Math. Soc. 72, 297--300 (1978; Zbl 0398.47040)]. For more interesting results in this direction, one may refer to the book [\textit{S. Czerwik}, Functional equations and inequalities in several variables (World Scientific, Singapore) (2002; Zbl 1011.39019)].