Fuzzy stability of a quadratic-additive functional equation (Q642236)

Summary: We investigate a fuzzy version of stability for the functional equation \[ \begin{multlined} f(x + y + z + w) + 2f(x) + 2f(y) + 2f(z) + 2f(w)\\ - f(x + y) - f(x + z) - f(x + w) - f(y + z) - f(y + w) - f(z + w) = 0.\end{multlined} \]