Q.If $A=\{1,2,3\},\ B=\{2,3,4\}$ then the function from $A$ to $B$ will be

Function: Definition and Identification

A function from a set $A$ to a set $B$ is a rule that assigns to each element of $A$ exactly one element of $B$. The set $A$ is the domain and $B$ is the codomain. The defining requirement is single-valuedness: no input may be linked to two different outputs. Written as a set of ordered pairs, a relation $f \subseteq A \times B$ is a function only if no two distinct pairs share the same first coordinate, and every element of $A$ appears as a first coordinate. …