Circumscription

Abstract

Like any other knowledge representation scheme, logic has to deal with the “problem of incomplete information”. The name given to the problem indicates that the world to be modelled can only be partially represented. The description of all propositions that are not true in the world to be modelled, which corresponds to an enormous collection of information, is highly problematic. An attractive solution is to make such knowledge implicit, by virtue of the Closed World Assumption [Reiter 1978b]:

$$\operatorname{if} \;A\;cannot\,be\;deduced\;then\;\inf er\; - A$$

(this is the formulation, in terms of logic, of the Closed World Assumption, where A is a ground atomic formula).