Hi,
What is different between:

1) OR V.S. ||
2) $_X V.S. $X
3) @session_start(); V.S. session_start();
4) if(!$X == Y) V.S. if($X != $Y)
5) if($X == $Y) V.S. if($X === $Y)
6) if($X == '') V.S. if($X == null)
7) die(''); V.S. exit();

?
Regards.