Splitting a default theory

This paper presents mathematical results that can sometimes be used to simplify the task of reasoning about a default theory, by "splitting it into parts." These so-called Splitting Theorems for default logic are related in spirit to "partial evaluation" in logic programming, in which results obtained from one part of a program are used to simplify the remainder of the program. In this paper we focus primarily on the statement and proof of the Splitting Theorems for default logic. We illustrate the usefulness of the results by applying them to an example default theory for commonsense reasoning about action.