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Youssef Aserrar, Elhoucien Elqorachi
In this paper, we determine the complex-valued solutions of the following functional equations \[g(xσ(y)) = g(x)g(y)+f(x)f(y),\quad x,y\in S,\]\[f(xσ(y)) = f(x)g(y)+f(y)g(x),\quad…