I want to keep only 1 fact with id=="aaaa". But this is not working:

rule "leave only one"

when

    $removeUs : java.util.List(size>1)

        from collect(Fact(id=="aaaa")

then

    size = $removeUs.size();

    for (int i=1; i < size; i++) {

        retract($removeUs.get(i));

    }

end