Given the next sets: $A=\{1,2\}$ , $B=\mathbb{N}$,
a) Describe all the functions from $A$ to $B$ that are not injective.
b) Describe all the functions from $B$ to $A$ that are not onto.
c) Prove or disprove the next:
(i) The next functions exist $f\colon A\to B$ and $g\colon B\to A$ if $g\circ f$ reversal
(ii) the next functions exist $f\colon A\to B$ and $g\colon B\to A$ if $f\circ g$ reversal
Need help here. Thanks.