type predicate_type =
  | PredicateType of string * int * string list;;

module PromiseSet = Set.Make(struct
  type t = predicate_type
  let compare p1 p2 = match (p1, p2) with (PredicateType(str1, ar1, list1), PredicateType(str2, ar2, list2)) -> (str1 = str2) && (ar1 = ar2) && (list1 = list2));;