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