function paginate_url_back()
{
    return Paginate::url_back();
}
 /**
  * Get url to access Previus page of find
  * 
  * @return string or null
  */
 static function url_back()
 {
     if (!empty(self::$url_back)) {
         return self::$url_back;
     }
     if (($back = self::page() - 1) < 1) {
         return null;
     }
     $query = Request::query_get('page', $back);
     $url = explode('?', Url::$current);
     return self::$url_back = $url[0] . '?' . $query;
 }