I have two objects with nested collections in my working memory. I need to determine if elements from one collection exist in the other collection. Here's an idea of what my objects look like: Class Foo: List<Token> tokens Class Bar: List<Token> tokens I'm putting instances of Foo and Bar into the working memory. A few days ago I got this generic suggestion but I'm not sure what it's actually doing: A( $colA : collection ) B( $colB : collection ) exists( Object( this memberOf $collectionB ) from $colA ) Can someone expand on that and explain what's happening? Any help is appreciated. Regards, Nick