Leonard J. Bass, Paul Young. Ordinal Hierarchies and Naming Complexity Classes. Journal of the ACM, 20(4):668-686, 1973. [doi]
@article{BassY73,
title = {Ordinal Hierarchies and Naming Complexity Classes},
author = {Leonard J. Bass and Paul Young},
year = {1973},
doi = {10.1145/321784.321793},
url = {http://doi.acm.org/10.1145/321784.321793},
researchr = {https://researchr.org/publication/BassY73},
cites = {0},
citedby = {0},
journal = {Journal of the ACM},
volume = {20},
number = {4},
pages = {668-686},
}