@inproceedings{Ginsburg_1967,
    doi = {10.1109/focs.1967.3},
    url = {https://doi.org/10.1109%2Ffocs.1967.3},
    year = {1967},
    publisher = {{IEEE}},
    author = {Seymour Ginsburg and Sheila Greibach},
    title = {Abstract families of languages},
    booktitle = {8th Annual Symposium on Switching and Automata Theory ({SWAT} 1967)}
}

@inproceedings{Ginsburg_1967, doi = {10.1109/focs.1967.3}, url = {https://doi.org/10.1109%2Ffocs.1967.3}, year = {1967}, publisher = {{IEEE}}, author = {Seymour Ginsburg and Sheila Greibach}, title = {Abstract families of languages}, booktitle = {8th Annual Symposium on Switching and Automata Theory ({SWAT} 1967)} }