1. P. Aczel, The ordinals of the superjump and related functionals, Abstract, this volume pp. 336f.
2. J. Barwise, R. Gandy and Y. Moschovakis, The next admissible set, J. Symb. Logic 36 (1971), 108–120.
3. R. B. Jensen and C. Karp, Primitive recursive set functions, in Axiomatic Set Theory, Part I, ed. Dana S. Scott, Amer. Math. Soc. Proceedings of Symposia in Pure Maths. (1971).
4. P. Mahlo, Über lineare transfinite Mengen, Berichte über die Verhandlungen der Königlich Sächsischen Gesellschaft der Wissenschaften zu Leipzig, Mathematisch-Physische Klasse 63 (1911), 187–225.
5. S. Kripke, Transfinite recursions on admissible ordinals, I, II, J. Symb. Logic 29 (1964), 161–162 (abstracts).