Mathematics as a language . I have forgotten my answer, but I remember finding her remark a shocking expression of profound ignorance. I don't even mean one book or one friend. I mean two or more. So did Plato.
None is the plain English meaning.
But the inconsistency can confuse students. In math lingo, a straight line is the simplest example of a curve. In math lingo, it may increase it, decrease it or neither, depending on whether you happen to be adding something positive, negative or zero. Correspondingly, subtracting decreases. In math lingo, it may decrease or increase or neither.