You shouldn't attempt to access external variables without first verifying that they exist, e.g. by using [man]isset/man.
As such, I usually define such variables like so:
$foo = (isset($_GET['foo']) ? $_GET['foo'] : NULL);
Note that in your code above, you're calling [man]isset/man after you've already attempted to access $_GET['page'] (by assigning its value to another variable).
