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 <WSD>be</WSD> a monotone function . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)