In mathematics, a function $f$ assigns each element of the set $D$, the domain, to exactly one element of the set $C$, the range. This assignment can be represented as follows: $ f: D \rightarrow C$ For example, the complex real variable function $f(x), x \in \mathbb{R}$ is represented as: $ f: \mathbb{R} \rightarrow \mathbb{C}$ The domain and range can be any [[set of numbers]].