PHP - Operasi Tanggal

<?php
$dt1 = 1;
$dt2 = date('d',strtotime('2011-12-16'));
echo "dt1 = $dt1 \n";
echo "dt2 = $dt2 \n";
echo "dt2 - dt1 = ".($dt2-$dt1)." \n";
for($dt1;$dt1<=$dt2;$dt1++){
        echo "$dt1 <= $dt2 \n";
}
?>