I am working through a description of gradient descent and I'm having trouble finding the definition of a couple notations, an arrow and a single quote, v→v′=v−η∇C. I normally express a derivative with a single quote f'(x) but that doesn't appear to be the case here.
The source of this equation is here http://neuralnetworksanddeeplearning.com/chap1.html, about 3/4 of the way down.
Thanks