Sheila A. Greibach. Comments on the roots of theorems and languages both easy and hard. SIGACT News, 13(1):26-29, 1981. [doi]
@article{Greibach81-0,
title = {Comments on the roots of theorems and languages both easy and hard},
author = {Sheila A. Greibach},
year = {1981},
doi = {10.1145/1008883.1008884},
url = {https://doi.org/10.1145/1008883.1008884},
researchr = {https://researchr.org/publication/Greibach81-0},
cites = {0},
citedby = {0},
journal = {SIGACT News},
volume = {13},
number = {1},
pages = {26-29},
}