@article{Urquhart_1999,
    doi = {10.1016/s0166-218x(99)00039-6},
    url = {https://doi.org/10.1016%2Fs0166-218x%2899%2900039-6},
    year = {1999},
    month = {oct},
    publisher = {Elsevier {BV}},
    volume = {96-97},
    pages = {177--193},
    author = {Alasdair Urquhart},
    title = {The symmetry rule in propositional logic},
    journal = {Discrete Applied Mathematics}
}

@article{Urquhart_1999, doi = {10.1016/s0166-218x(99)00039-6}, url = {https://doi.org/10.1016%2Fs0166-218x%2899%2900039-6}, year = {1999}, month = {oct}, publisher = {Elsevier {BV}}, volume = {96-97}, pages = {177--193}, author = {Alasdair Urquhart}, title = {The symmetry rule in propositional logic}, journal = {Discrete Applied Mathematics} }