 A different set of issues arises in connection with the behavior of default logic from the point of view of computation. For a given semi-decidable set \(\Phi\) of sentences, the set of all \(\phi\) that are a consequence of \(\Phi\) in FOL is itself semi-decidable (see the entry on  computability and complexity).  In the case of default logic, to formulate the corresponding problem one extends (in the obvious way) the notion of (semi-)decidability to sets of defaults. The problem, then, is to decide, given a default theory \((\Gamma,\Delta)\) and a sentence φ whether \((\Gamma,\Delta) \nc \phi\), where \(\nc\) is defined, say, skeptically. Such a problem is not even semi-decidable, since, in order to determine whether a default is triggered by a pair of sets of sentences, one has to perform a consistency check, and such checks are not computable. 