1. Aristotle. Prior and Posterior Analytics. Everyman’s Library, Dutton: New York, 1964; original ≈344 B.C. Edited and translated by John Warrington.
2. Bible. The Holy Bible. Collins’ Clear Type Press. King James Translation, Genesis, chapter 11.
3. Charniak, Eugene and McDermott, Drew. Introduction to Artificial Intelligence. Addison-Wesley, 1985.
4. Dujet, Ch. and Vincent, N. Force implication: A new approach to human reasoning. Fuzzy Sets and System, 69:53–63, 1995.
5. Fenstad, Jens Erik and Normann, Dag. Innfring i Matematisk Logikk. Institute of Mathematics, University of Oslo, 1988. In Norwegian.