public function alter()
 {
     if (!isset($_SESSION['logged'])) {
         return call('pages', 'home');
     } else {
         if (!isset($_GET['code'])) {
             return call('pages', 'error', 2);
         }
         $sources = Sources::all();
         $requirement = Requirement::get($_GET['code']);
         require_once 'views/requirements/alter.php';
     }
 }