Elements of Statistical Learning - question on p. 18 In the following expression:




What do $E_{X}$ and $E_{Y|X}$ mean, respectively?


In case helpful, I note that the authors derived that expression from the following:




Based on the above, how would one conclude that that minimizing $EPE(f)$ can be accomplished as follows?
Maybe this helps:

On YouTube, there's a video with explanations for the main topics in Introduction to Statistical Learning (sorry, not for ELS).

https://www.youtube.com/watch?v=3jQs02dbfrI