In mathematics, a function is a binary relation between two sets that associates each element of the first set to exactly one element of the second set. Typical examples are functions from integers to integers or from the real numbers to real numbers. A function is a process or a relation that associates each element x of a set X, the domain of the function, to a single element y of another set Y (possibly the same set), the function's codomain. It is customarily denoted by letters such as f, g and h. A function is uniquely represented by the set of all pairs (x, f (x)), called the function's graph. When the domain and the codomain are real numbers, each such pair may be thought of as the Cartesian coordinates of a point in the plane.