@article{Ritchie_1972,
    doi = {10.1016/s0019-9958(72)90205-7},
    url = {https://doi.org/10.1016%2Fs0019-9958%2872%2990205-7},
    year = {1972},
    month = {may},
    publisher = {Elsevier {BV}},
    volume = {20},
    number = {4},
    pages = {313--330},
    author = {R.W. Ritchie and F.N. Springsteel},
    title = {Language recognition by marking automata},
    journal = {Information and Control}
}

@article{Ritchie_1972, doi = {10.1016/s0019-9958(72)90205-7}, url = {https://doi.org/10.1016%2Fs0019-9958%2872%2990205-7}, year = {1972}, month = {may}, publisher = {Elsevier {BV}}, volume = {20}, number = {4}, pages = {313--330}, author = {R.W. Ritchie and F.N. Springsteel}, title = {Language recognition by marking automata}, journal = {Information and Control} }