+(* takes 3 lists of alive ids (they are threated the same way, the type is
+ * funny just to not oblige you to concatenate them) and drops all the dead
+ * equalities *)
+val collect: equality_bag -> int list -> int list -> int list -> unit
+
+(* given an equality, returns the numerical id *)
+val id_of: equality -> int
+
+(* profiling statistics *)
+val get_stats: unit -> string
+