php - how prevent include 2 times but if not included before include now -

i have 1 file named header-guest.php
when open link http://royta.ir/badurl
code run:

if(!isset($headerload)){ if(isset($_cookie['userid'])){     include_once('tmp/header.php'); } else{     include_once('tmp/header-guest.php'); } } 

and when click on بازگشت به خانه
ajax code run in #content

if(!isset($headerload)){ if(isset($_cookie['userid'])){     include_once('tmp/header.php'); } else{     include_once('tmp/header-guest.php');     include_once('block/index-visitor.php'); } } 

and in header-guest.php have code

<? echo $sitetitle; $headerload = 1;?> 

but when click on badurl , click on بازگشت به خانه
header-guest.php run 2 times
how prevent it?

to prevent loading resources twice use require_once or include_once . prevent resource being loaded twice if happen put 2 include_once statements same resource.