1. W. Ackermann. Zur Widerspruchsfreiheit der reinen Zahlentheorie. Mathematische Annalen
117, 1940.
2. T. Arai. A slow growing analogue to Buchholz’ proof. Annals of Pure and Applied Logic 54 (1991), 101–120.
3. T. Arai. Proof theory for theories of ordinals. Preprint, Hiroshima, 1995.
4. B. Blankertz and A. Weiermann. A uniform characterization of the provably total functions of KPM and some of its subsystems. Preprint, Münster (1995). To appear in: Proceedings of the Logic Colloquium 1994.
5. W. Buchholz. Three contributions to the conference on “Recent advances in Proof Theory”. Oxford, April, 10–16, 1980, (mimeographed).