Define a function as a correspondence between two sets.
Function as a correspondence between two sets: Let A and B be two non – empty sets. Then, a function ‘f’ from set A to set B is a correspondence (rule) which
associates elements of set A to elements of set B such that:
(i) all elements of set A are associated with an element in set B.
(ii) an element of set A is associated with a unique element in set B.