Hermann K.-G. Walter. Die Verwandtschaft kontextfreier Grammatiken. Computing, 22(1):31-58, 1979. [doi]
@article{Walter79-1, title = {Die Verwandtschaft kontextfreier Grammatiken}, author = {Hermann K.-G. Walter}, year = {1979}, doi = {10.1007/BF02246558}, url = {http://dx.doi.org/10.1007/BF02246558}, researchr = {https://researchr.org/publication/Walter79-1}, cites = {0}, citedby = {0}, journal = {Computing}, volume = {22}, number = {1}, pages = {31-58}, }