# How to do this index notation differentiation?

I am studying classical Maxwell fields and I am stuck on this differentiating part. How can I derive the result given below ?

$$\dfrac{\partial}{\partial(\partial A_{\mu}/\partial x_{\nu})} \left(2\dfrac{\partial A_{\sigma}}{\partial x_{\lambda}}\dfrac{\partial A_{\sigma}}{\partial x_{\lambda}}-2\dfrac{\partial A_{\sigma}}{\partial x_{\lambda}}\dfrac{\partial A_{\lambda}}{\partial x_{\sigma}}\right)$$

$$4\dfrac{\partial A_{\mu}}{\partial x_{\nu}}-4\dfrac{\partial A_{\nu}}{\partial x_{\mu}}$$
where $A$ is vector potential and $x$ is four-vector.
Hint: try writing $\frac{\partial A_\mu}{\partial x_\lambda}=T_\mu^\lambda$ and similarly for different indices. –  Danu Mar 13 at 18:22