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xkcd #2943: Unsolved Chemistry Problems
(imgs.xkcd.com)
Alt text:
I'm an H⁺ denier, in that I refuse to consider loose protons to be real hydrogen, so I personally believe it stands for 'pretend'.
Exponents and Logarithms can be first taught in Middle School in many places, but sometimes get revisited during Calculus in AP High School or at University level.