anchor.diff:  
   type stack = list<stack_elt>
   
  -
  +let is_fstar_tactics_embed t =
  +    match (U.un_uinst t).n with
  +    | Tm_fvar fv -> S.fv_eq_lid fv SC.fstar_refl_embed_lid
  +    | _ -> false
   
   let mk t r = mk t None r
   let set_memo r t =
  
positive.code:             | Tm_type u ->
                mk (Tm_type (norm_universe cfg env u)) t.pos
  
              | Tm_uinst(t, us) -> (* head symbol must be an fvar *)
                mk_Tm_uinst t (List.map (norm_universe cfg env) us)
  
              | Tm_bvar x ->
                begin match lookup_bvar env x with
  
negative.code:       true
      | _ ->
        false
  
  let rec norm : cfg -> env -> stack -> term -> term =
      fun cfg env stack t ->
  