$use "RF_Stack" StdIO;

$func F e = ;

F {
  t1 e2 =
    <WriteLN <Depth>>,
    <F e2>,
    <WriteLN <Depth>>;
  /*empty*/ = <WriteLN <Depth> !>;
};

Main =
  <WriteLN <Depth>>,
  <F I I I>,
  <WriteLN <Depth>>;