anchor.diff:              match l with
               | Success (_, gl, _ as gs) :: _ ->
                   print_goalstate 1 gs
  -            | Error _ :: _ -> Format.print_string "Erroneous goalstate"
  +            | Error _ :: _ -> Format.print_string "Erroneous goalstack"
               | [] -> Format.print_string "Empty goalstack"
           | _ -> 
               match l with
  
positive.code:         | [] -> INSTANTIATE_ALL i th
          | _ -> Choice.failwith "CONTR_TAC.propagate_thm: Unhandled case."
      fun cth (asl, w) -> 
          try 
              let th = CONTR w cth
              (null_meta, [], propagate_thm th)
              |> Choice.result
          with
          | Failure _ -> Choice.failwith "CONTR_TAC: Failure."
  
  /// Solves a goal which is an instance of the supplied theorem.
  let (MATCH_ACCEPT_TAC : thm_tactic) =
  
negative.code:     (if fvs <> []
       then 
           let errmsg = end_itlist (fun s t -> s + ", " + t) fvs
           warn true ("Free variables in goal: " + errmsg)
       else ())
      set_goal([], t)
  
  