Consider an axiom of the form (P -> Q). If P is true, we might want the system to go ahead and conclude Q. On the other hand, we might want it just to verify that Q is true and complain if it is not. If later Q is retracted, we might want the system to immediately complain, or to detect this at its leisure. All this is indicated by placing instances of the collection assertion conclusion type as the arg2 of the predicate assertion conclusion action type, with the rule in question being the arg1. See the comments on the instances of the collection assertion conclusion type for further details.