anchor.diff:     aux false (whnf env t1)
   
   let base_and_refinement env t = base_and_refinement_maybe_delta false env t
  -let normalize_refinement steps env wl t0 = N.normalize_refinement steps env t0
  +let normalize_refinement steps env t0 = N.normalize_refinement steps env t0
   
   let unrefine env t = base_and_refinement env t |> fst
   
  
positive.code:         let reduce_one_and_try_again (d1:delta_depth) (d2:delta_depth) =
            let d1_greater_than_d2 = Common.delta_depth_greater_than d1 d2 in
            let t1, t2 = if d1_greater_than_d2
                         then let t1' = normalize_refinement [N.UnfoldUntil d2; N.Weak; N.HNF] env wl t1 in
                              t1', t2
                         else let t2' = normalize_refinement [N.UnfoldUntil d1; N.Weak; N.HNF] env wl t2 in
                              t1, t2' in
            aux retry (n_delta + 1) t1 t2
          in
  
negative.code:           match Common.decr_delta_depth d with
            | None -> fail n_delta r t1 t2
            | Some d ->
              let t1 = normalize_refinement [N.UnfoldUntil d; N.Weak; N.HNF] env t1 in
              let t2 = normalize_refinement [N.UnfoldUntil d; N.Weak; N.HNF] env t2 in
              aux retry (n_delta + 1) t1 t2
          in
  
  