anchor.diff:                              (Print.term_to_string t2) in
       try
               let res = Rel.teq_nosmt env t1 t2 in
  -            debug_off(); res
  -    with | _ -> debug_off(); false
  -
  -//    try Rel.teq_nosmt env t1 t2
  -//    with | _ -> false
  -
  -let trysolve (goal : goal) (solution : term) : bool =
  +            debug_off();
  +            ret res
  +    with | Errors.Err (_, msg) -> begin
  +            debug_off();
  +            mlog (fun () -> BU.print1 ">> do_unify error, (%s)\n" msg ) (fun _ ->
  +            ret false)
  +            end
  +         | Errors.Error (_, msg, r) -> begin
  +            debug_off();
  +            mlog (fun () -> BU.print2 ">> do_unify error, (%s) at (%s)\n"
  +                                msg (Range.string_of_range r)) (fun _ ->
  +            ret false)
  +            end
  +
  +let trysolve (goal : goal) (solution : term) : tac<bool> =
       do_unify goal.context solution goal.witness
   
   let dismiss : tac<unit> =
  
positive.code: let change (ty : typ) : tac<unit> = wrap_err "change" <|
      mlog (fun () -> BU.print1 "change: ty = %s\n" (Print.term_to_string ty)) (fun _ ->
      bind cur_goal (fun g ->
      if do_unify g.context g.goal_ty ty
      then replace_cur ({ g with goal_ty = ty })
      else begin
          (* Give it a second try, fully normalize the term the user gave
  
negative.code:              let body = S.bv_to_name bv in
               let lbs, body = SS.close_let_rec [lb] body in
               let tm = mk (Tm_let ((true, lbs), body)) None goal.witness.pos in
               bind (trysolve goal tm) (fun bb ->
               if bb
               then bind (replace_cur ({ goal with context = env';
                                                   goal_ty = bnorm env' (comp_to_typ c);
                                                   witness = bnorm env' u})) (fun _ ->
                    ret (S.mk_binder bv, b))
               else fail "intro_rec: unification failed"
               ))
      | None ->
          fail1 "intro_rec: goal is not an arrow (%s)" (tts goal.context goal.goal_ty)
      )
  