anchor.diff:          let pairwise t1 t2 wl =
               if Env.debug env <| Options.Other "Rel"
               then BU.print2 "[meet/join]: pairwise: %s and %s\n" (Print.term_to_string t1) (Print.term_to_string t2);
  -            let mr, ts = head_matches_delta env () t1 t2 in
  +            let mr, ts = head_matches_delta env t1 t2 in
               match mr with
               | HeadMatch true
               | MisMatch _ ->
  
positive.code:     | _ -> MisMatch(delta_depth_of_term env t1, delta_depth_of_term env t2)
  
  (* Does t1 head-match t2, after some delta steps? *)
  let head_matches_delta env wl t1 t2 : (match_result * option<(typ*typ)>) =
      let maybe_inline t =
          let head = U.head_of t in
          if Env.debug env <| Options.Other "RelDelta" then
  
negative.code:                         (Print.tag_of_term t2)
                          (Print.term_to_string t1)
                          (Print.term_to_string t2);
          let m, o = head_matches_delta env t1 t2 in
          match m, o  with
          | (MisMatch _, _) -> //heads definitely do not match
              let rec may_relate head =
  