 Friedgut junta inequality

If $f:\{-1,1{\}}^n\to \{-1,1\}$ satisfies $\Vert f^{\le k}{\Vert }_2^2\ge 1-\epsilon$, then it has a real-valued $J$-junta approximation $g$ with $\Vert f-g{\Vert }_2^2\le 2\epsilon$ and