C. P. Rupert. Commutative regular languages. SIGACT News, 22(4):48-49, 1991. [doi]
@article{Rupert91-0, title = {Commutative regular languages}, author = {C. P. Rupert}, year = {1991}, doi = {10.1145/126546.126547}, url = {https://doi.org/10.1145/126546.126547}, researchr = {https://researchr.org/publication/Rupert91-0}, cites = {0}, citedby = {0}, journal = {SIGACT News}, volume = {22}, number = {4}, pages = {48-49}, }