+let symmetric eq_ty l id uri m =
+ let eq = Cic.MutInd(uri,0,[]) in
+ let pred =
+ Cic.Lambda (Cic.Name "Sym",eq_ty,
+ Cic.Appl [CicSubstitution.lift 1 eq ;
+ CicSubstitution.lift 1 eq_ty;
+ Cic.Rel 1;CicSubstitution.lift 1 l])
+ in
+ let prefl =
+ Exact (Cic.Appl
+ [Cic.MutConstruct(uri,0,1,[]);eq_ty;l])
+ in
+ let id1 =
+ let eq = mk_equality (0,prefl,(eq_ty,l,l,Utils.Eq),m) in
+ let (_,_,_,_,id) = open_equality eq in
+ id
+ in
+ Step(Subst.empty_subst,
+ (Demodulation,id1,(Utils.Left,id),pred))
+;;
+
+module IntOT = struct
+ type t = int
+ let compare = Pervasives.compare
+end
+
+module IntSet = Set.Make(IntOT);;
+
+let n_purged = ref 0;;
+
+let collect alive1 alive2 alive3 =
+ let _ = <:start<collect>> in
+ let deps_of id =
+ let p,_,_ = proof_of_id id in
+ match p with
+ | Exact _ -> IntSet.empty
+ | Step (_,(_,id1,(_,id2),_)) ->
+ IntSet.add id1 (IntSet.add id2 IntSet.empty)
+ in
+ let rec close s =
+ let news = IntSet.fold (fun id s -> IntSet.union (deps_of id) s) s s in
+ if IntSet.equal news s then s else close news
+ in
+ let l_to_s s l = List.fold_left (fun s x -> IntSet.add x s) s l in
+ let alive_set = l_to_s (l_to_s (l_to_s IntSet.empty alive2) alive1) alive3 in
+ let closed_alive_set = close alive_set in
+ let to_purge =
+ Hashtbl.fold
+ (fun k _ s ->
+ if not (IntSet.mem k closed_alive_set) then
+ k::s else s) id_to_eq []
+ in
+ n_purged := !n_purged + List.length to_purge;
+ List.iter (Hashtbl.remove id_to_eq) to_purge;
+ let _ = <:stop<collect>> in ()
+;;
+
+let id_of e =
+ let _,_,_,_,id = open_equality e in id
+;;
+
+let get_stats () =
+ <:show<Equality.>> ^
+ "# of purged eq by the collector: " ^ string_of_int !n_purged ^ "\n"
+;;