9. let x = {1, 2, 3}, y = {1, 2, 3, 4}, and z = {1, 2}. a. define a function f : x → y that is one-to-one but not onto. b. define a function g: x → z that is onto but not one- to-one. c. define a function h: x → x that is neither one-to-one nor onto. d. define a function k: x → x that is one-to-one and onto but is not the identity function on x.