Earlier quoted context omitted.
I taught mathematics for 30 years at the college level. This is a college level textbook and it is not appropriate for either high school or middle school. Very few students at that level would be able to understand this material.
Discrete Math it's far easier than Calculus with infinitesimals, limits and curves everywhere. As a programmer with Lisp experienc but not HS-er, I'd say that any kid learning Python would be at home with Discrete Math, or most Elementary kids playing RPG's/JRPG's at home.
With discrete math, there are really no unifying themes.