Why start at x, y, z? A collection of mathematical ...

> Reverse Polish Notation: The expression ( x − 2 ) ( x − 1 ) would be written instead × − x 2 − x 1 , or something like that.

This is not reverse Polish notation.

It's Polish notation; parentheses free prefix notation.

The reverse would be x 2 － x 1 － ×.

I've contacted the author to let him know -- thanks.

well... i've yet to read this through, but likely this is THE thing that made calculus and linear algebra so hard for me (learning discrete math was definitely worth it too, but still!)

And THE THE thing thing is bad teaching. If you fail to establish a sound basis of the language used to convey meaning the outcome is doomed to be miserable.

This is a collection of ambiguous, inconsistent, or just unpleasant conventions in mathematical notation.