The collection non abducible collection is a sub-collection of intensional or extensional set. Abductive inferences sometimes involve hypothesizing the existence of entities as part of the explanation of some assertion or set of assertions. Cyc will not hypothesize the existence of instances of the collections that are instances of non abducible collection. Roughly, abductive inferences consume conceptual / theoretical knowledge rather than produce it. So, second-order Cyc collection is an instance of non abducible collection because Cyc should be employing existing theoretical knowledge about instances of second-order Cyc collection rather than hypothesizing new instances.