 To compare the concepts, if A is recursively enumerable then there is a sequence of recursive sets Ai such that each Ai is a subset of A with each Ai growing monotonically, approaching A in the limit. But if A is only defeasibly enumerable then the Ai’s still approach A in the limit but may not be subsets of A and approach A intermittently from above and below. The goal of the OSCAR Project (Pollock 1989) is to construct a general theory of rationality and implement it in an artificial computer-based rational agent. As such, the system uses a defeasible automated reasoner that operates according to the maxim that the set of warranted beliefs should be defeasible enumerable. OSCAR has been in the making for some time and the application of automated nonmonotonic reasoning has also been used to extend its capabilities to reason defeasibly about perception and time, causation, and decision-theoretic planning (Pollock 2006). 