Tweety - Still Flying: Some Remarks on Abnormal Birds Applicable Rules and a Default Prover

This paper describes FAULTY, a default prover for a decidable subset of predicate calculus. FAULTY is based on McDermott s and Doyle's Nonmonotonic Logic I and avoids the well-known weakness of this logic by a restriction to specific theories, which are sufficient for default reasoning purposes, however. The defaults are represented in a way that allows explicit control of their applicability. By blocking the applicability of a default the problem of interacting defaults can be avoided.