condition to check if the session variables as well as get and post have been destroyed in php -

the code like:(it last page of web-app have made)

<?php  if(isset($_get['var']) { session_start(); $a=$_session['prev_defined']; #more use of session variable session_destroy(); $_session = array(); unset($_get); unset($_post); } ?> 

now when execute web application runs fine , when refresh last page code given above warning message shows of undefined symbol because $_session variables $_get , $_post have been deleted. want display message "session over" on refresh. how it? put if condition? have tried put above code in

if($_session) { #entire code above } else { echo"session over"; } 

but displayes message undefined variable _session

<?php  if(isset($_get['var']) {   if(isset($_session))   {     session_start();     $a=$_session['prev_defined'];     #more use of session variable     session_destroy();     $_session = array();     unset($_get);     unset($_post);   }   else   {     echo"session over";   } } ?> 

try one. if session set conditions.

edit

if(isset($_get['var'])     { .... } else   {     echo"session over";   } 

using this, if $_get['var'] not set echo else part

edit 2

<?php if (isset($_get) || isset($_session)) { //put codes here } else {     echo "session over"; }