文摘
Let \({(S,\cdot)}\) be a semigroup, (H, +) an abelian group and \({f: S \to H}\). The first and second order Cauchy differences of f are $$\begin{aligned} C^{1}f(x, y)= & {} f(xy) - f(x) - f(y),\\ C^{2}f(x, y, z)= & {} f(xyz) - f(xy) - f(yz) - f(xz) + f(x) + f(y) + f(z).\end{aligned}$$Higher order Cauchy differences C k f are defined recursively. In the case of H = R, a ring where multiplication is distributive over addition, we show that functions \({f: S\to R}\) with vanishing finite Cauchy differences are closed under multiplication. The equation C k f = 0 is considered for cyclic groups, free abelian groups and other selected quotients of the free groups. Keywords Functional equations semigroups rings Cauchy differences free abelian groups factorization quotient groups Mathematics Subject Classification Primary 39B42 39B52 Secondary 39A70 39B72 Dedicated to Professor Roman Ger on his seventieth birthday