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:                         (Print.tag_of_term t2)
                          (Print.term_to_string t1)
                          (Print.term_to_string t2);
          let m, o = head_matches_delta env wl t1 t2 in
          match m, o  with
          | (MisMatch _, _) -> //heads definitely do not match
              let rec may_relate head =
  
negative.code:                             if pat_discriminates b
                              then
                                let (_, _, t') = SS.open_branch b in
                                match head_matches_delta env s t' with
                                | FullMatch, _
                                | HeadMatch _, _ ->
                                  true
  