To be fair , this is partly to blame on the given formula . If it was written as EX XP or EXxX xPXx it would probably be easier to see that X refers to the random variable and does not mean replace all the xi s . Mathematics has lots of great notation that can make things a lot shorter to write down , but I somewhat agree with the author they can be rather confusing to figure out , if one does not understand the underlying mathematics . P . S . I also hate the EX 2 notation , as I ' m one of those persons who prefer powers to denote composition instead of multiplication for functions although composition with itself rarely makes sense for random variables . <| sep |> I have 3 of these bad boys 😂 I ' m so pissed man . But I could do shadow Bonnie and pink boomerang for kurama if you want