The Inconsistency of a Belief Revision System

In 1987 Chern Seet developed a belief revision algorithm and a deduction system by which, he claims, default reasoning can be accomplished. We show that his deduction system is inconsistent. Some obvious corrections are suggested but the resulting system is still inconsistent. Its behaviour is similar to that of a closed-world- assumption reasoner. We examine a case in which the modified system behaves like the predicate circumscription and also has a reasonable performance. Finally, we discuss some problems pertaining to Seet's revision strategy. A similar revision algorithm for normal default logic is outlined and the use of the SET model for handling exceptions --- and default reasoning --- is briefly discussed.