1. Fitting, M.C.: Types, Tableaus, and Gödel’s God (2000), Available on my website comet.lehman.cuny.edu/fitting
2. Fitting, M.C., Mendelsohn, R.: First-Order Modal Logic. Kluwer, Dordrecht (1998); Paperback (1999)
3. Kripke, S.: Naming and Necessity. Harvard University Press, Cambridge (1980)
4. Ullman, J.D.: Principles of Database and Knowledge-Base Systems, vol. 1. Computer Science Press, Rockville (1988)