type 'status tactic = #tac_status as 'status -> 'status
+module NCicInverseRelIndexable : Discrimination_tree.Indexable
+with type input = cic_term and type constant_name = NUri.uri = struct
+
+open Discrimination_tree
+
+type input = cic_term
+type constant_name = NUri.uri
+
+let ppelem = function
+ | Constant (uri,arity) ->
+ "("^NUri.name_of_uri uri ^ "," ^ string_of_int arity^")"
+ | Bound (i,arity) ->
+ "("^string_of_int i ^ "," ^ string_of_int arity^")"
+ | Variable -> "?"
+ | Proposition -> "Prop"
+ | Datatype -> "Type"
+ | Dead -> "Dead"
+;;
+
+let path_string_of (ctx,t) =
+ let len_ctx = List.length ctx in
+ let rec aux arity = function
+ | NCic.Appl ((NCic.Meta _|NCic.Implicit _)::_) -> [Variable]
+ | NCic.Appl (NCic.Lambda _ :: _) -> [Variable] (* maybe we should b-reduce *)
+ | NCic.Appl [] -> assert false
+ | NCic.Appl (hd::tl) ->
+ aux (List.length tl) hd @ List.flatten (List.map (aux 0) tl)
+ | NCic.Lambda _ | NCic.Prod _ -> [Variable]
+ (* I think we should CicSubstitution.subst Implicit t *)
+ | NCic.LetIn _ -> [Variable] (* z-reduce? *)
+ | NCic.Meta _ | NCic.Implicit _ -> assert (arity = 0); [Variable]
+ | NCic.Rel i -> [Bound (len_ctx - i, arity)]
+ | NCic.Sort (NCic.Prop) -> assert (arity=0); [Proposition]
+ | NCic.Sort _ -> assert (arity=0); [Datatype]
+ | NCic.Const (NReference.Ref (u,_)) -> [Constant (u, arity)]
+ | NCic.Match _ -> [Dead]
+ in
+ aux 0 t
+;;
+
+let compare e1 e2 =
+ match e1,e2 with
+ | Constant (u1,a1),Constant (u2,a2) ->
+ let x = NUri.compare u1 u2 in
+ if x = 0 then Pervasives.compare a1 a2 else x
+ | e1,e2 -> Pervasives.compare e1 e2
+;;
+
+let string_of_path l = String.concat "." (List.map ppelem l) ;;
+
+end
+
+module Ncic_termOT : Set.OrderedType with type t = cic_term =
+ struct
+ type t = cic_term
+ let compare = Pervasives.compare
+ end
+
+module Ncic_termSet : Set.S with type elt = cic_term = Set.Make(Ncic_termOT)
+
+module InvRelDiscriminationTree =
+ Discrimination_tree.Make(NCicInverseRelIndexable)(Ncic_termSet)
+
type 'status tactic = #tac_status as 'status -> 'status
+(* indexing facilities over cic_term based on inverse De Bruijn indexes *)
+
+module NCicInverseRelIndexable : Discrimination_tree.Indexable
+with type input = cic_term and type constant_name = NUri.uri
+
+module Ncic_termSet : Set.S with type elt = cic_term
+
+module InvRelDiscriminationTree : Discrimination_tree.DiscriminationTree
+with type constant_name = NCicInverseRelIndexable.constant_name
+and type input = NCicInverseRelIndexable.input
+and type data = Ncic_termSet.elt and type dataset = Ncic_termSet.t
+
(* end *)