(* Copyright (C) 2000, 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/.
 *)

exception UnificationFailed
exception Free
exception OccurCheck

(* The entry (i,t) in a substitution means that *)
(* (META i) have been instantiated with t.      *)
type substitution = (int * Cic.term) list

(* fo_unif metasenv context t1 t2                *)
(* unifies [t1] and [t2] in a context [context]. *)
(* Only the metavariables declared in [metasenv] *)
(* can be used in [t1] and [t2].                 *)
val fo_unif :
  Cic.metasenv -> Cic.context -> Cic.term -> Cic.term ->
   substitution * Cic.metasenv

(* apply_subst subst t                    *)
(* applies the substitution [sust] to [t] *)
val apply_subst : substitution -> Cic.term -> Cic.term

(* apply_subst_reducing subst (Some (mtr,reductions_no)) t              *)
(* performs as (apply_subst subst t) until it finds an application of   *)
(* (META [mtr]) that, once unwinding is performed, creates a new        *)
(* beta-redex; in this case up to [reductions_no] consecutive           *)
(* beta-reductions are performed.                                       *)
(* Hint: this function is usually called when [reductions_no]           *)
(*  eta-expansions have been performed and the head of the new          *)
(*  application has been unified with (META [meta_to_reduce]):          *)
(*  during the unwinding the eta-expansions are undone.                 *)
val apply_subst_reducing :
 substitution -> (int * int) option -> Cic.term -> Cic.term