\begin{definition}[Definition:Center of Symmetry]
Let $\FF$ be a geometric figure.
A '''center of symmetry''' $C$ of $\FF$ is a point such that:
:every point $P$ of $\FF$ has a corresponding point $P'$ which is also in $\FF$ such that $C$ is the midpoint of the straight line segment $PP'$.
\end{definition}