(*
    ||M||  This file is part of HELM, an Hypertextual, Electronic        
    ||A||  Library of Mathematics, developed at the Computer Science     
    ||T||  Department, University of Bologna, Italy.                     
    ||I||                                                                
    ||T||  HELM is free software; you can redistribute it and/or         
    ||A||  modify it under the terms of the GNU General Public License   
    \   /  version 2 or (at your option) any later version.      
     \ /   This software is distributed as is, NO WARRANTY.     
      V_______________________________________________________________ *)

module Subst (B : Terms.Blob) = struct
  
  let id_subst = [];;
  
  let build_subst n t tail = (n,t) :: tail ;;
  
  let rec lookup_subst var subst =
    match var with
      | Terms.Var i ->
          (try
            lookup_subst (List.assoc i subst) subst
          with
              Not_found -> var)
      | _ -> var
  ;;
  let lookup_subst i subst = lookup_subst (Terms.Var i) subst;;
  
  let is_in_subst i subst = List.mem_assoc i subst;;
  
  (* filter out from metasenv the variables in substs *)
  let filter subst varlist =
    List.filter
      (fun m ->
         not (is_in_subst m subst))
      varlist
  ;;
  
end