\begin{definition}[Definition:Parallelepiped/Opposite Face]
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The '''opposite face''' of the face $F$ of a parallelepiped $P$ is the face of $P$ which is parallel to $F$.
In the above example, the pairs of parallel planes are:
:Face $ABCD$ is opposite $HGFE$
:Face $ADEH$ is opposite $BCFG$
:Face $ABGH$ is opposite $DCFE$
\end{definition}