Functions
Functions are mappings or assignments.
Contents
Description
A function maps every member of A to a member of B. Or, for each x ∈ A a function assigns a unique f(x) ∈ B. Such a function is notated as f : A -> B.
The image of a function f is the subset of B that corresponds to the entire domain of A: f(A) = {f(x) | x ∈ A}. The inverse image or pre-image is the subset of A that corresponds to the entire domain of B: f -1(B) = {x | f(x) ∈ B}.
Note that there is a difference between inverse images and a true inverse. A unique inverse of a function only exists if it is bijective. An inverse satisfies f(f -1(x)) = x.
Functions can be composed. For two functions as f : A -> B and g : B -> C, f ∘ g corresponds to (f ∘ g)(x) = f(g(x)).