Mapping

A mapping M: D → R specifies a correspondence between elements of a domain D and a range R.

If each element of D maps to exactly one element of R, and that element R is mapped to only by that one element of D, the mapping is one-to-one or injective .

If every element of R is mapped to by some element of D, the mapping is onto or surjective .

A mapping that is both one-to-one and onto is bijective.