Let $f:\left( { - 1,1} \right) \to R$ be a differentiable function with $f\left( 0 \right) = - 1$ and $f'\left( 0 \right) = 1$. Let $g\left( x \right) = {\left[ {f\left( {2f\left( x \right) + 2} \right)} \right]^2}$. Then $g'\left( 0 \right) = $