-val add_lt_constraint: NCic.universe -> NCic.universe -> unit
-val add_leq_constraint: NCic.universe -> NCic.universe -> unit
+(* add_constraint raise BadConstraint in case of universe inconsistency
+ or if the second argument is an inferred universe
+ true -> strict check (<); false -> loose check (<=)
+*)
+val add_constraint: bool -> NCic.universe -> NCic.universe -> unit
+val sup : NCic.universe -> NCic.universe option
+val pp_constraints: unit -> string