anchor.diff:              %% Create new receive expression adding the `after 0` part.
               Timeout = erl_syntax:integer(0),
               %% Create new variable to use as 'Aux'.
  -            [{used, Used}] = ets:lookup(?NT_USED, used),
  -            Fresh = erl_syntax_lib:new_variable_name(Used),
  -            FunVar = erl_syntax:variable(Fresh),
  +            FunVar = new_variable(),
               Action = erl_syntax:application(FunVar, []),
               NewRecv = erl_syntax:receive_expr(NewClauses, Timeout, [Action]),
               %% Create a new fun to be the argument of rep_receive.
  
positive.code: instrument_yield() ->
      erl_syntax:atom(true).
  
  %% Log a list of errors, as returned by compile:file/2.
  log_error_list(List) ->
      log_list(List, "").
  
negative.code: 	receive_expr ->
  	    instrument_receive(instrument_subtrees(Tree));
  	%% Replace every underscore with a new (underscore-prefixed) variable.
  	underscore -> new_underscore_variable();
  	_Other -> instrument_subtrees(Tree)
      end.
  
  