PHP/Cookie Session/session is registered
session_is_registered() checks whether or not a variable has been registered.
<source lang="html4strict">
Its syntax is: boolean session_is_registered (string varname)
<? session_start(); if (! session_is_registered("hits")) :
session_register("hits");
endif; $hits++; print "You"ve seen this page $hits times"; ?>
</source>