Grzegorz Rozenberg, Dirk Vermeir. A hierarchy of ETOL languages with rank. Fundamenta Informaticae, 4(1):197, 1981.
@article{RozenbergV81, title = {A hierarchy of ETOL languages with rank}, author = {Grzegorz Rozenberg and Dirk Vermeir}, year = {1981}, researchr = {https://researchr.org/publication/RozenbergV81}, cites = {0}, citedby = {0}, journal = {Fundamenta Informaticae}, volume = {4}, number = {1}, pages = {197}, }