anchor.diff:                     || S.fv_eq_lid f PC.false_lid)
                   then false
                   else begin
  -                  if not (Option.isSome cfg.steps.unfold_only) || Option.isSome cfg.steps.unfold_attr
  -                  then
                       let attr_eq a a' = match U.eq_tm a a' with | U.Equal -> true | _ -> false in
                       should_delta &&
                       (match cfg.steps.unfold_only with
  
positive.code:                  let stack = us::stack in
                   norm cfg env stack t'
  
            | Tm_fvar f ->
              let should_delta =
                  cfg.delta_level |> BU.for_some (function
  
negative.code:                     | Eager_unfolding_only -> true
                      | Unfold l -> Common.delta_depth_greater_than f.fv_delta l) in
              let should_delta =
                  if cfg.steps.unfold_tac &&
                     (  S.fv_eq_lid f PC.and_lid
                     || S.fv_eq_lid f PC.or_lid
                     || S.fv_eq_lid f PC.imp_lid
  