\begin{definition}[Definition:Complements of Parallelograms]
Let $ABDC$ and $EFHG$ be two parallelograms with the same angles, which share a diagonal, such that $ABDC \cap EFHG \ne \O$.
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Then the two parallelograms $CIGK$ and $BJHL$ are known as the '''complements''' of the parallelograms $ABDC$ and $EFHG$.
\end{definition}