@article{GDZPPN002043998,
title = {A characterization of Takeuti's ordinal diagrams of finite order.},
journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
volume = {9},
year = {1971},
pages = {75-98},
zbl = {0244.02011},
url = {http://dml.mathdoc.fr/item/GDZPPN002043998}
}
Schütte, Kurt; Levitz, Hilbert. A characterization of Takeuti's ordinal diagrams of finite order.. Archiv für mathematische Logik und Grundlagenforschung, Tome 9 (1971) pp. 75-98. http://gdmltest.u-ga.fr/item/GDZPPN002043998/