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+(* Copyright (C) 2005, HELM Team.
+ * 
+ * This file is part of HELM, an Hypertextual, Electronic
+ * Library of Mathematics, developed at the Computer Science
+ * Department, University of Bologna, Italy.
+ * 
+ * HELM is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ * 
+ * HELM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HELM; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA  02111-1307, USA.
+ * 
+ * For details, see the HELM World-Wide-Web page,
+ * http://cs.unibo.it/helm/.
+ *)
+
+(* $Id$ *)
+
+module type EqualityIndex =
+  sig
+    module PosEqSet : Set.S with type elt = Utils.pos * Inference.equality
+    val arities : (Cic.term, int) Hashtbl.t
+    type key = Cic.term
+    type t = Discrimination_tree.DiscriminationTreeIndexing(PosEqSet).t
+    val empty : t
+    val retrieve_generalizations : t -> key -> PosEqSet.t
+    val retrieve_unifiables : t -> key -> PosEqSet.t
+    val init_index : unit -> unit
+    val remove_index : t -> Inference.equality -> t
+    val index : t -> Inference.equality -> t
+    val in_index : t -> Inference.equality -> bool
+  end
+
+module DT = 
+struct
+    module OrderedPosEquality = struct
+	type t = Utils.pos * Inference.equality
+	let compare = Pervasives.compare
+      end
+
+    module PosEqSet = Set.Make(OrderedPosEquality);;
+    
+    include Discrimination_tree.DiscriminationTreeIndexing(PosEqSet)
+    
+
+    (* DISCRIMINATION TREES *)
+    let init_index () =
+      Hashtbl.clear arities;
+    ;;
+
+    let remove_index tree equality = 
+      let _, _, (_, l, r, ordering), _, _ = equality in
+	match ordering with
+	  | Utils.Gt -> remove_index tree l (Utils.Left, equality)
+	  | Utils.Lt -> remove_index tree r (Utils.Right, equality)
+	  | _ -> 
+	      let tree = remove_index tree r (Utils.Right, equality) in
+		remove_index tree l (Utils.Left, equality)
+
+    let index tree equality = 
+      let _, _, (_, l, r, ordering), _, _ = equality in
+	match ordering with
+	  | Utils.Gt -> index tree l (Utils.Left, equality)
+	  | Utils.Lt -> index tree r (Utils.Right, equality)
+	  | _ -> 
+	      let tree = index tree r (Utils.Right, equality) in
+		index tree l (Utils.Left, equality)
+  
+
+    let in_index tree equality = 
+      let _, _, (_, l, r, ordering), _, _ = equality in
+      let meta_convertibility (pos,equality') = 
+	Inference.meta_convertibility_eq equality equality' 
+      in
+	in_index tree l meta_convertibility || in_index tree r meta_convertibility
+
+  end
+
+module PT = 
+  struct
+    module OrderedPosEquality = struct
+	type t = Utils.pos * Inference.equality
+	let compare = Pervasives.compare
+      end
+
+    module PosEqSet = Set.Make(OrderedPosEquality);;
+    
+    include Discrimination_tree.DiscriminationTreeIndexing(PosEqSet)
+    
+
+    (* DISCRIMINATION TREES *)
+    let init_index () =
+      Hashtbl.clear arities;
+    ;;
+
+    let remove_index tree equality = 
+      let _, _, (_, l, r, ordering), _, _ = equality in
+	  match ordering with
+	  | Utils.Gt -> remove_index tree l (Utils.Left, equality)
+	  | Utils.Lt -> remove_index tree r (Utils.Right, equality)
+	  | _ -> 
+	      let tree = remove_index tree r (Utils.Right, equality) in
+		remove_index tree l (Utils.Left, equality)
+
+    let index tree equality = 
+      let _, _, (_, l, r, ordering), _, _ = equality in
+	match ordering with
+	  | Utils.Gt -> index tree l (Utils.Left, equality)
+	  | Utils.Lt -> index tree r (Utils.Right, equality)
+	  | _ -> 
+	      let tree = index tree r (Utils.Right, equality) in
+		index tree l (Utils.Left, equality)
+  
+
+    let in_index tree equality = 
+      let _, _, (_, l, r, ordering), _, _ = equality in
+      let meta_convertibility (pos,equality') = 
+	Inference.meta_convertibility_eq equality equality' 
+      in
+	in_index tree l meta_convertibility || in_index tree r meta_convertibility
+end
+