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