Vlad, The conditional element "not" is the oposite of "exists". It means exactly what you want: not MyObject( <constraints> ) Will evaluate to true if and only if there is no instance of MyObject in the working memory that match the given <constraints>. Exists will evaluate to true if there is at least one object that matches the constraints: exists MyObject( <constraints> ) So, you don't need to write "not exists"... write simply "not". Having said that, 3.0.x will trigger an error if you write "not exists". Trunk will "optimize" and remove your "exists" effectivelly using only the "not". []s Edson Olenin, Vladimir (MOH) wrote: -- Edson Tirelli Software Engineer - JBoss Rules Core Developer Office: +55 11 3124-6000 Mobile: +55 11 9218-4151 JBoss, a division of Red Hat @ www.jboss.com