1. A. Beller, R. Jensen and P. Welch, Coding the Universe, London Mathematical Society, Lecture Notes Series, vol. 47, Cambridge University Press, Cambridge, 1982.
2. S. Friedman, A guide to ‘Coding the universe’ by Beller, Jensen, Welch, J. Symbolic Logic 50
(1985), 1002–1019.
3. D. Law, Doctoral dissertation, California Institute of Technology (to appear).