Abstract Boundedness and the Stability of the Pexider Equation

Let (S, +) be a semigroup (not necessarily Abelian) and let (X,+) be a commutative group. We deal with an axiomatically given family B ⸦ 2x of "bounded sets" and with mappings f, g, h : S → X such that the transformation S x S ∋ (x, y) → f (x + y) - g (x) - h (y) ∈ X remains B-bounded. Stability results existing in the literature in connection with the Pexider functional equation become special cases of our theorems up to the magnitude of approximating constants.