On Open Defaults (1990)
In Reiter's default logic, the parameters of a default are treated as metavariables for ground terms. We propose an alternative definition of an extension for a default theory, which handles parameters as genuine object variables. The new form of default logic may be preferable when the domain closure assumption is not postulated. It stands in a particularly simple relation to circumscription. Like circumscription, it can be viewed as a syntactic transformation of formulas of higher order logic.
In Computational Logic: Symposium Proceedings, Lloyd, John (Eds.), pp. 80-95 1990. Springer.

Vladimir Lifschitz Faculty vl [at] cs utexas edu