[rules-users] Erratic behaviour of Drools

Hello, I am a little bit confused as I don't get what I am doing wrong. Here is my rule: ************************** rule "Exchange Pattern" when $p2: ProcessAdapter() $mainProcess: ProcessAdapter( isMainProcess(), this!=$p2) MessageFlowAdapter ( fromProcess == $mainProcess, toProcess==$p2) MessageFlowAdapter ( fromProcess == $p2, toProcess==$mainProcess) exists ItemAwareElementAdapter( ) from $mainProcess.getReceivedResources($p2) exists ItemAwareElementAdapter( ) from $mainProcess.getGivenResources($p2) then System.out.println("** FOUND EXCHANGE PATTERN betwwen "+$mainProcess.getParticipant().getName()+" AND "+$p2.getParticipant().getName()); System.out.println("Given: "+$mainProcess.getGivenResources($p2)+$mainProcess.getGivenResources($p2).size()); System.out.println("Received: "+$mainProcess.getReceivedResources($p2)+$mainProcess.getReceivedResources($p2).size()); System.out.println("Intersection: "+$mainProcess.intersectGivenAndReceivedResourcesWithProcess($p2)+$mainProcess.intersectGivenAndReceivedResourcesWithProcess($p2).size()); end ************************** This rule is never fired, although I know it should. When I comment out the ONE OF the two "exists" constraints, I get this output: ************************** ** FOUND EXCHANGE PATTERN betwwen Amazon AND Ship.Comp. Given: [Products (ID:DataObjectReference_2)]1 Received: [Products (ID:DataObjectRefeference_GEN7)]1 Intersection: [Products (ID:DataObject_2)]1 ************************** two "exists" constrains as both conditions are met, but it doesn't. I am kind of new to Drools so I may be doing an horrible mistake but google haven't been my friend so far. Any help will be very appreciated! Thanks. Anis