Show that for every \(z\in\{0,1\}^{n}\), there exists a value \(f^{\prime}(z)\) such that \(\Pr_{r}[f(z+r)+f(r)=f^{\prime}(z)]\geq\frac{1}{2}+\sqrt{\frac{1}{4}-\epsilon}\). (so the probability tends to 1 as \(\epsilon\) approaches zero)