\begin{definition}[Definition:Rubik's Cube/Edge Facet]
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Of each of the $9$ facets of each face of Rubik's cube, the $4$ on the edges of the face are called the '''edge facets'''.
The set of '''edge facets''' can be denoted $S_E$.
For example:
:$fu$, $fr$, $fd$, $fl$ are the '''edge facets''' of the front face
:$ul$, $ub$, $ur$, $uf$ are the '''edge facets''' of the up face
and so on.
\end{definition}