PROGRAM

  ROUTINE trace
  BEGIN
    FORWARD 70;
    ROTATE 45;
  END

  ROUTINE trace1
  BEGIN
  CALL trace;
  CALL trace;
  END

  ROUTINE trace2
  BEGIN
  CALL trace1;
  CALL trace1;
  END

  ROUTINE trace3
  BEGIN
  CALL trace2;
  CALL trace2;
  END

BEGIN
  FORWARD 100;
  ROTATE 90;
  FORWARD 100;
  ROTATE 270;
  PEN DOWN;
  CALL trace3;
END.