\begin{definition}[Definition:Rubik's Cube/Corner Facet]
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Of each of the $9$ facets of each face of Rubik's cube, the $4$ in the corners of the face are called the '''corner facets'''.
The set of '''corner facets''' can be denoted $S_C$.
For example:
:$flu$, $fru$, $frd$, $fld$ are the '''corner facets''' of the front face
:$ulb$, $urb$, $urf$, $ulf$ are the '''corner facets''' of the up face
and so on.
\end{definition}