Undefined index: _page

[didi00]

Hi guys,
I'm trying to use an individual CMS. But when I installed it it shows me this notice:

NOTICE: UNDEFINED INDEX: _PAGE IN C:\WAMP\WWW\MYCMS.PHP ON LINE 16

The php file is this:

<?php

if ($_SERVER["REQUEST_URI"]) {
	if (is_array($tmp = explode("?" , $_SERVER["REQUEST_URI"]))) {
		$tmp = explode("&" , $tmp["0"]);
		foreach ($tmp as $key => $val) {
			$_tmp = explode("=" , $val);

			if ($_tmp[0]) {
				$_GET[$_tmp[0]] = urldecode($_tmp[0]);
			}			
		}		
	}	
}

$_PAGE = $_GET["_PAGE"];
$_ADMIN = false;

require "admin/config.php";
?>

With what should I replace the _PAGE, so that I won't have any errors?
Thanks.

[didi00]

It is done!
Here is the code that need to be replaced on line 16:

$_PAGE = (isset($_GET['_PAGE']) ? strtolower($_GET['_PAGE']) : NULL);