How to redirect to referrer from Observer in Magento ?

we can redirect to the referrer from magento observer like below

Mage::getSingleton('core/session')->addError('your error message'); // to show your message after redirection
$url = Mage::helper('core/http')->getHttpReferer() ? Mage::helper('core/http')->getHttpReferer()  : Mage::getUrl();
Mage::app()->getFrontController()->getResponse()->setRedirect($url);
Mage::app()->getResponse()->sendResponse();
exit ;