A Monotonicity Theorem for Extended Logic Programs

Because general and extended logic programs behave nonmonotonically, it is in general diicult to predict how even minor changes to such programs will aaect their meanings. This paper shows that for a restricted class of extended logic programs | those with signings | it is possible to state a fairly general theorem comparing the entailments of programs. To this end, we generalize (to the class of extended logic programs) the deenition of a signing, rst formulated by Kunen for general programs, and establish a theorem characterizing a restricted monotonicity property for signed extended programs. The theorem is formulated in terms of simple syntactic criteria on pairs of programs. To demonstrate the usefulness of this result, we use it to compare the strengths of two families of extended logic programs for commonsense reasoning about action.