let cmp_of_rel x y = function
| Rlt -> S.is_included x y && not (equal x y), uncomparable x y
| Rgt -> S.is_included y x && not (equal x y), uncomparable x y
| Rle -> S.is_included x y, uncomparable x y
| Rge -> S.is_included y x, uncomparable x y
| Req -> S.equal x y , uncomparable x y
| Rneq -> uncomparable x y, S.equal x y