Sentence:  For it is clear that the total number of ordinary intersections of C and **f must be even ( otherwise , starting in the interior of C , **f could not finally <WSD>return</WSD> 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:  go or come back to place, condition, or activity where one has been before