Thus, f is one-one Also, any odd number
2r + 1 in the co-domain N is the image of 2r + 2 in the domain N and any even number
2r in the co-domain N is the image of 2r – 1 in the domain N Thus, f is onto Example 13 Show that an onto function f : {1, 2, 3} → {1, 2, 3} is always one-one