On extending endomorphisms to automorphisms. Levitz, Hilbert; Nichols, Warren — 1988 International Journal of Mathematics and Mathematical Sciences
A Characterization of the Veblen-Schütte Functions by Means of Functionals Hilbert Levitz — 1973 Commentarii mathematici Helvetici
On the Finsler and Doner-Tarski Arithmetical Hierarchies. Hilbert Levitz — 1969 Commentarii mathematici Helvetici
Über die FINSLERschen höheren arithmetischen Operationen. Hilbert Levitz Commentarii mathematici Helvetici
Ordinal Bounds for Well Ordered Extensions of the Coordinatewise Partial Ordering Hilbert Levitz — 1976 Commentarii mathematici Helvetici
The Cartesian product of sets and the Hessenberg natural product of ordinals Hilbert Levitz — 1979 Czechoslovak Mathematical Journal
A characterization of Takeuti's ordinal diagrams of finite order. Kurt Schütte; Hilbert Levitz — 1971 Archiv für mathematische Logik und Grundlagenforschung