eqBox (t,_) (t',_) | t == t'   = return () -- Type, Label, Enum
                    | otherwise = fail "Different terms"
eqBox (t,_) (t',_) | t == t'   = return () -- Type, Label, Enum
                    | otherwise = fail "Different terms"
eqBox (t,_) (t',_) | t == t'   = return () -- Type, Label, Enum
                    | otherwise = fail "Different terms"