@inproceedings{Pa77a,
AUTHOR = {Paul, W.J.},
TITLE = {On Time Hierarchies},
YEAR = {1977},
PAGES = {218--222},
BOOKTITLE = {Proc. 9th ACM-STOC 1977},
EE = {http://doi.acm.org/10.1145/800105.803411},
}