> His definition of linear is also wrong in my book. There are two variations of "linear function". To quote https://en.wikipedia.org/wiki/Linear_function http

> His definition of linear is also wrong in my book. There are two variations of "linear function". To quote https://en.wikipedia.org/wiki/Linear_function https://en.wikipedia.org/wiki/Linear_function: > In mathematics, the term linear function refers to two distinct but related notions: > - In calculus and related areas, a linear function is [...] a polynomial function of degree one or zero. > - In linear algebra, mathematical analysis, and functional analysis, a linear function is a linear map. I personally prefer the terminology "linear function" for the former definition (polynomials of degree 1 or 0), and "linear transform" for the latter definition (a linear map).