public function User_delete($user)
 {
     $sql = sprintf("DELETE FROM {$this->dbTableNamePrefix}" . LTI_Data_Connector::USER_TABLE_NAME . ' ' . 'WHERE (consumer_key = %s) AND (context_id = %s) AND (user_id = %s)', LTI_Data_Connector::quoted($user->getResourceLink()->getKey()), LTI_Data_Connector::quoted($user->getResourceLink()->getId()), LTI_Data_Connector::quoted($user->getId(LTI_Tool_Provider::ID_SCOPE_ID_ONLY)));
     $ok = mysql_query($sql);
     if ($ok) {
         $user->initialise();
     }
     return $ok;
 }