\begin{definition}[Definition:Periodic Function/Periodic Element]
Let $f: X \to X$ be a function, where $X$ is either $\R$ or $\C$.
Let $L \in X_{\ne 0}$.
Then $L$ is a '''periodic element''' of $f$ {{iff}}:
:$\forall x \in X: \map f x = \map f {x + L}$
Category:Definitions/Periodic Functions
\end{definition}