@article{Gradel:JSL:1999,
    doi = {10.2307/2586808},
    url = {https://doi.org/10.2307%2F2586808},
    year = {1999},
    month = {dec},
    publisher = {Cambridge University Press ({CUP})},
    volume = {64},
    number = {4},
    pages = {1719--1742},
    author = {Erich Grädel},
    title = {On the Restraining Power of Guards},
    journal = {Journal of Symbolic Logic}
}

@article{Gradel:JSL:1999, doi = {10.2307/2586808}, url = {https://doi.org/10.2307%2F2586808}, year = {1999}, month = {dec}, publisher = {Cambridge University Press ({CUP})}, volume = {64}, number = {4}, pages = {1719--1742}, author = {Erich Grädel}, title = {On the Restraining Power of Guards}, journal = {Journal of Symbolic Logic} }