@article{Tor_n_1991,
    doi = {10.1145/116825.116858},
    url = {https://doi.org/10.1145%2F116825.116858},
    year = {1991},
    month = {jul},
    publisher = {Association for Computing Machinery ({ACM})},
    volume = {38},
    number = {3},
    pages = {752--773},
    author = {Jacobo Tor{\'{a}}n},
    title = {Complexity classes defined by counting quantifiers},
    journal = {Journal of the {ACM}}
}

@article{Tor_n_1991, doi = {10.1145/116825.116858}, url = {https://doi.org/10.1145%2F116825.116858}, year = {1991}, month = {jul}, publisher = {Association for Computing Machinery ({ACM})}, volume = {38}, number = {3}, pages = {752--773}, author = {Jacobo Tor{\'{a}}n}, title = {Complexity classes defined by counting quantifiers}, journal = {Journal of the {ACM}} }