Operational Characterization of Extensions in Some Logics for Default Reasoning

Default reasoning is one of the most common forms of nonmonotonic reasoning, and is found in many application domains. Default logic and its variants have been proposed as knowledge representation methods capable of default reasoning. One problem of all these methods is that their concepts are given in terms of fixed-point equations, thus making them difficult to understand and use. In this paper, we present simple, constructive approaches for the semantics of some default logic variants, and show their correctness.