Accessible open textbooks in math-heavy disciplines

Try reading physics books that introduce the maths as an instrument (e.g. Wald’s General relativity to learn tensor calculus, you only need the first few chapters), they usually explain concepts and notation in simpler terms. However, they may hide stuff under the rug of “it’s a tradition”, “we do this, don’t ask questions”, “ margin is too narrow to contain the proof”, etc.

P.S.: Greek alphabet is not that bad (it’s only 24 letters, and a third of them isn’t used on behalf of being the same as some Latin ones), just look it up. It’s much worse when some mathematician in the 19th century invents his own squiggly to refer to a pretty useful function.