@article{Gruska_1971,
    doi = {10.1016/s0019-9958(71)90095-7},
    url = {https://doi.org/10.1016%2Fs0019-9958%2871%2990095-7},
    year = {1971},
    month = {oct},
    publisher = {Elsevier {BV}},
    volume = {19},
    number = {3},
    pages = {216--223},
    author = {J. Gruska},
    title = {A few remarks on the index of context-free grammars and languages},
    journal = {Information and Control}
}

@article{Gruska_1971, doi = {10.1016/s0019-9958(71)90095-7}, url = {https://doi.org/10.1016%2Fs0019-9958%2871%2990095-7}, year = {1971}, month = {oct}, publisher = {Elsevier {BV}}, volume = {19}, number = {3}, pages = {216--223}, author = {J. Gruska}, title = {A few remarks on the index of context-free grammars and languages}, journal = {Information and Control} }