1. How a computer should think;Belnap,1977
2. A useful four-valued logic;Belnap,1977
3. Generic terms and generic sentences;Carlson;J. Philos. Logic,1982
4. Formalizing nonmonotonic reasoning systems;Etherington;Artificial Intelligence,1987
5. NETL: A System for Representing and Using Real-World Knowledge;Fahlman,1979