A characterization of Takeuti's ordinal diagrams of finite order. Kurt Schütte, Hilbert Levitz (1971) Archiv für mathematische Logik und Grundlagenforschung
A Characterization of the Veblen-Schütte Functions by Means of Functionals Hilbert Levitz (1973) Commentarii mathematici Helvetici
A partition theorem for α-large sets Teresa Bigorajska, Henryk Kotlarski (1999) Fundamenta Mathematicae
A well-ordering proof for Feferman's theory To. Gerhard Jäger (1983) Archiv für mathematische Logik und Grundlagenforschung
An application of results by Hardy, Ramanujan and Karamata to Ackermannian functions. Weiermann, Andreas (2003) Discrete Mathematics and Theoretical Computer Science. DMTCS [electronic only]