@article{Ginsburg_1970,
    doi = {10.1016/s0022-0000(70)80016-2},
    url = {https://doi.org/10.1016%2Fs0022-0000%2870%2980016-2},
    year = {1970},
    month = {aug},
    publisher = {Elsevier {BV}},
    volume = {4},
    number = {4},
    pages = {308--338},
    author = {Seymour Ginsburg and Sheila Greibach},
    title = {Principal {AFL}},
    journal = {Journal of Computer and System Sciences}
}

@article{Ginsburg_1970, doi = {10.1016/s0022-0000(70)80016-2}, url = {https://doi.org/10.1016%2Fs0022-0000%2870%2980016-2}, year = {1970}, month = {aug}, publisher = {Elsevier {BV}}, volume = {4}, number = {4}, pages = {308--338}, author = {Seymour Ginsburg and Sheila Greibach}, title = {Principal {AFL}}, journal = {Journal of Computer and System Sciences} }