Program DNull;

Procedure O;

Var
  Null: Char = 'O';

begin (* O *)
  write ( Null );
end (* O *);

Procedure K ( Var x: Integer );

begin (* K *)
  if @x = Nil then
    writeln ( 'K' )
  else
    writeln ( 'failed' );
end (* K *);

begin
  O;
  K ( Null );
end.
