1. A. B. Anderson and N. D. Belnap, Jr., Entailment, vol. 1, Princeton, 1975.
2. N. D. Belnap, Jr., How a computer should think, forthcoming in Contemporary Aspects of Philosophy. (Proceedings of the Oxford International Symposium, (1975).
3. N. D. Belnap, Jr., A useful four-valued logic, forthcoming in Modern Uses of Multiple ? Valued Logic, eds. T. Epstein and J. M. Dunn.
4. C. C. Chang and H. J. Keisler, Model Theory, Amsterdam, 1973.
5. J. M. Dunn, An intuitive semantics for first-degree entailments and ?coupled trees?, Philosophical Studies 29 (1976), pp. 149?68.