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