the generator distribution is nonzero everywhere that allows us to say that the derivatives of pg are equal to P G times the derivatives of log P G so that gives us this nice expression where we can get a gradients of the likelihood in terms of samples that came out of the generator but what would you really like is gradients of the likelihood in terms of samples that came from the data so the way that we're able to do that is important sampling we have this f of X coefficient that we're able to multiply by each of the gradients and we can fix