Hypothetical Reasoning with Well Founded Semantics

Well Founded Semantics is shown adequate to capture hypothetical reasoning if we interpret the Well Founded model of a program P as a (possibly incomplete) view of the world. Thus the Well Founded model may be accepted as a partially definite view of the world, and the other extended stable models as alternative extended consistent views of the world. The original contributions of this paper are: showing that Well Founded Semantics is useful for representing hypothetical reasoning problems; to present a framework for representing always within the language itself: definite, default and generally applicable rules; preference among defaults; exceptions to rules; exceptions to exceptions; abduction; and integrity constraints.