Edgar T. Irons. Structural connections in formal languages. Communications of the ACM, 7(2):67-72, 1964. [doi]
@article{Irons64, title = { Structural connections in formal languages}, author = {Edgar T. Irons}, year = {1964}, doi = {10.1145/363921.363931}, url = {http://doi.acm.org/10.1145/363921.363931}, researchr = {https://researchr.org/publication/Irons64}, cites = {0}, citedby = {0}, journal = {Communications of the ACM}, volume = {7}, number = {2}, pages = {67-72}, }