how to answer

Show that the function of Example 2.20 is not one-to-one. (Example 2.20: Let F be the set of all nonempty finite sets of integers, so F C of P(Z). Define a function s: F > Z by setting 5(X) to be the sum of all the elements of X.) o s({1, 2, 4}) = -1 = s({4, 1, 2}) but {1, 2, 4} + {4, 1, 2}. For all x F there is no subset of Z such that s(x) = 0. Consider the sets a = {1, 2, 3} and b = {3, 2, 1}. s(a@) = 6 = 5(b). Therefore, a O s({1, 2h) = 3 = s({3}) but {1, 2} + {3}. O For any y Z there is {y} F and s({y}) = y