o
Function : many-one ( Not injective )
o Function that is not one-one is many-one .
Function : onto ( or surjective )
A function f : X → Y is said to be onto ( or surjective ), if every element of Y is the image of some element of X under f , i . e ., for every y ∈ Y , there exists an element x in X such that f ( x ) = y .