Inverse entailment (IE) is known as a technique for finding inductive hypotheses in Horn theories. When a background theory
is nonmonotonic, however, IE is not applicable in its present form. The purpose of this paper is extending the IE technique
to nonmonotonic inductive logic programming (ILP). To this end, we first establish a new entailment theorem in normal logic
programs, then introduce the notion of contrapositive programs. Finally, a theory of IE in nonmonotonic ILP is constructed.