Sentence:  Thus if e is sufficiently small , there can be only one intersection of C and **f near Q , for if there were more than one intersection for every e then the difference between C and **f near Q would not be a monotone <WSD>function</WSD> . 
Meaning of the word marked with <WSD> tags:  (mathematics) a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)