1. J. Barwise, editor. Handbook of Mathematical Logic, volume 90 of Studies in Logic and the Foundations of Mathematics. North Holland, 1977.
2. Kenneth Kunen. Set Theory: An Introduction to Independence Proofs. North Holland, 1980.
3. A. Smith. On Recursive Free Types in Z. RSRE Memorandum 91028. MOD PE, RSRE, 1991.
4. J.M. Spivey. Understanding Z. Cambridge University Press, 1988.
5. J.M. Spivey. The Z Notation: A Reference Manual Prentice-Hall, 1989.