Consider A = {1, 2, 3, 4} and B = {2, 3, 5, 9}. Is the relation f = {(1, 2), (2, 3), (3, 3), (3, 5)} a function from A to B?
The element 4 in A does not have an image. ....………… (1)
The element 3 is mapped to both 3 and 5. …………..... (2)
From (1) and (2), f is not a function.