In a complete function, the output of the inside function is the input of the outside function. That is, in f{g{x}}, the output of g{x} is the input of f{x}.
The composition of the functions f (x) and g (x) is defined as: (f ° g) (x) = f [g (x) ]. That means that the output of the function g (x) is the input of the function f (x).
