Sentence:  For it is clear that the total number of <WSD>ordinary</WSD> intersections of C and **f must be even ( otherwise , starting in the interior of C , **f could not finally return to the interior ) , and the center of rotation at t is the argument of the function , not a value . 
Meaning of the word marked with <WSD> tags:  not exceptional in any way especially in quality or ability or size or degree