# ON MULTI-JENSEN FUNCTIONS AND JENSEN DIFFERENCE

• Published : 2008.11.30

#### Abstract

In this paper we characterize multi-Jensen functions f : $V^n\;{\rightarrow}\;W$, where n is a positive integer, V, W are commutative groups and V is uniquely divisible by 2. Moreover, under the assumption that f : $\mathbb{R}\;{\rightarrow}\;\mathbb{R}$ is Borel measurable, we obtain representation of f (respectively, f, g, h : $\mathbb{R}\;{\rightarrow}\;\mathbb{R}$) such that the Jensen difference $$2f\;$\frac{x\;+\;y}{2}$\;-\;f(x)\;-\;f(y)$$ (respectively, the Pexider difference $$2f\;$\frac{x\;+\;y}{2}$\;-\;g(x)\;-\;h(y))$$ takes values in a countable subgroup of $\mathbb{R}$.

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