In the book of "Introduction_to_the_Theory_of_Computation_by_Michael_Sipser_Third_Edition_Course_Technology", Page 7, last sentence is "A function that use all the elements of the range is said to be noto the range." What doe it mean by "use"? How can a function uses its element of its range? Can you please give an example ? Thank you so much in advance!
"In the case of the function abs, if we are working with integers, the domain and the range are Z, so we write abs : Z−!Z. In the case of the addition function for integers, the domain is the set of pairs of integers Z × Z and the range is Z, so we write add : Z × Z−!Z. Note that a function may not necessarily use all the elements of the specified range. The function abs never takes on the value −1 even though −1 2 Z. A function that does use all the elements of the range is said to be onto the range."