If f and g are bijective, then g f is bijective. Assume f and g are injective. Left as exercise. If you take the SSN of a person, and then lookup the person having this SSN, you will get back the original person. That is, composing the function SSN and the function SSN -1 yields the identity.
T be a function.
T , then g is called the inverse function of f , and is denoted f -1 . 1.8 Functions and counting 1.8.1 Injections, surjections, bijections and cardinality of sets Example 9 You distribute n different cakes between k child. Suppose f is injective. Suppose f is surjective. Suppose f is bijective.