hi all, This code could not be parsed correctly: rule "out" when Msg(!(set not contains "test")) then end I tried a few simple situations and found that when using 'not contains' operator in a '!' leading quote triggers this problem. If no '!' prefixing the quote,the program works like a charm... Is this a bug? I wish that I posted in the right forum(or I would go to submit an issue?).. The example above seemed so stupid(you can use a 'contains' operator instead), but this is the simplest toy example.And this problem would be looked more important if you want to write some logic like this: Msg(!(set not contains "test" || !bool && string == "hello")) So... Is there anyone who also encountered this problem? I'm using drools 5.3.0 final. Any help would appreciated. Thanks! -- Regards. Miles. Wen