Answer by
john11 (617)

take a function y = f(x) where x takes on a set of values. Let these numbers be whole numbers (1,2,3,4,5,6,7) for simplicity. What y = f(x) means is that y equals some transformations to those whole numbers. If we let y = x + 2, then {x=1,y=3;x=2,y=4;x=3;y=5} for instance.