(FrontFace _ _ _ _) +++ (FrontFace _ _ _ _) = CornerPointsError "illegal FrontFace +++ FrontFace operation"
(FrontFace _ _ _ _) +++ (FrontFace _ _ _ _) = CornerPointsError "illegal FrontFace +++ FrontFace operation"
(FrontFace _ _ _ _) +++ (FrontFace _ _ _ _) = CornerPointsError "illegal FrontFace +++ FrontFace operation"