A typical way to define a function f from a set S, called the domain of the function, to a set T, called the range, is that f is a relationship between S to T that relates one and only one member of T...A typical way to define a function f from a set S, called the domain of the function, to a set T, called the range, is that f is a relationship between S to T that relates one and only one member of T to each element of X. We use f(x) to stand for the element of T that is related to the element x of S. If we wanted to make our definition more precise, we could substitute the word “relation” for the word “relationship” and we would have a more precise definition.