1. Barwise, K. J., Infinitary logic and admissible sets, Dissertation, Stanford University, 1967.
2. Transfinite recursive progressions of axiomatic theories;Feferman;J. Symb. Logic,1962
3. Systems of predicative analysis;Feferman;J. Symb. Logic,1964
4. Predicative provability in set theory, (Research Announcement);Feferman;Bull. Am. Math. Soc.,1966
5. Systems of predicative analysis II: Representations of ordinals;Feferman;J. Symb. Logic,1968