I was going through the paper on GAN by Ian Goodfellow. Under the related work section, there is an equation. I cannot decipher the equation. Can anyone help me understand the meaning of the equation?
$$\lim_{\sigma \to 0} \nabla_{\mathbf x} \mathbb E_{\epsilon \sim \mathcal N(0, \sigma^2 \mathbf I)} f(\mathbf x+\epsilon) = \nabla_x f(\mathbf x)$$
Also, any guide to understanding mathematical notation for reading research paper areis highly appreciated.
$$\lim_{\sigma \to 0} \nabla_{\mathbf x} \mathbb E_{\epsilon \sim \mathcal N(0, \sigma^2 \mathbf I)} f(\mathbf x+\epsilon) = \nabla_x f(\mathbf x)$$