Jane Terry Nutter
This paper presents a simple extension of first order predicate logic to include a default operator. Rules of inference governing the operator are specified, and a model theory for interpreting sentences involving default operstor is developed based on standard Tarslian semantics. The Resulting system is trivially sound. It is argued that (a) this logic provides an adequate basis for default reasoning in A.I. systems, and (b) unlike most logics proposed for this purpose, it retains the virtues of standard first order logic, including both montonicity and simplicity.