1. Begr�ndung des ?tertium non datur? mittels der Hilbertschen Theorie der Widerspruchsfreiheit
2. Epsilon substitution method for theories of jump hierarchies. Preprint.
3. Ordinal analysis without proofs. To appear in: Re\015ections: A collection honoring Solomon Feferman on his 70th birthday, ASL Lecture Notes in Logic, AK Peters, Natick (MA).
4. An ordinal analysis of admissible set theory using recursion on ordinal notations. Submitted.
5. The witness function method and provably recursive functions of Peano arithmetic. In: Proceedings of the Ninth International Congress on Logic, Methodology, and Philosophy of Science (D. Westerståhl, D. Prawitz, and B. Skyrms, eds.), Elsevier Science, Amsterdam 1994, pp. 29 - 68.