A function f : A -> B is surjective or onto or a surjection if f A = B.I.e. f can return any value in B. This means that its image is its codomain.Only surjections have right inverses, f': B -> A where f (f'x) = x since if f were not a surjection there would be elements of B for which f'was not defined.See also bijection, injection.(1995-05-27)