anchor.diff:      {[], N}.
   
   label_vars([T | Ts], N, Env) ->
  -    Env1 = dict:store(var_name(T), N, Env),
  +    Env1 = Env#{var_name(T) => N},
       {As, N1} = label_ann(T, N),
       T1 = set_ann(T, As),
       {Ts1, N2, Env2} = label_vars(Ts, N1, Env1),
  
positive.code: 	    %% Constant literals are not labeled.
  	    {T, N};
  	var ->
              {As, N1} =
                  case dict:find(var_name(T), Env) of
  		    {ok, L} ->
  		        {A, _} = label_ann(T, L),
  		        {A, N};
                      error ->
  		        label_ann(T, N)
                  end,
  	    {set_ann(T, As), N1};
  
negative.code: -spec label(cerl:cerl(), integer()) -> {cerl:cerl(), integer()}.
  
  label(T, N) ->
      label(T, N, #{}).
  
  label(T, N, Env) ->
      case type(T) of
  