create a trigger expression like :

{Host:key.last(0)}

=0 +

{Host:key.last(0)}

>1

try to test it in the trigger testing window :

Parse error: syntax error, unexpected ';' in /home/main/usr/local/apache2/htdocs/trunk/tr_testexpr.php(144) : eval()'d code on line 1

Undefined index: result[/home/main/usr/local/apache2/htdocs/trunk/tr_testexpr.php:141]
Undefined index: result[/home/main/usr/local/apache2/htdocs/trunk/tr_testexpr.php:141]