@article{Wrathall_1991,
    doi = {10.1016/0166-218x(91)90101-2},
    url = {https://doi.org/10.1016%2F0166-218x%2891%2990101-2},
    year = {1991},
    month = {jul},
    publisher = {Elsevier {BV}},
    volume = {32},
    number = {2},
    pages = {211--222},
    author = {C. Wrathall},
    title = {Trace monoids with some invertible generators: two decision problems},
    journal = {Discrete Applied Mathematics}
}

@article{Wrathall_1991, doi = {10.1016/0166-218x(91)90101-2}, url = {https://doi.org/10.1016%2F0166-218x%2891%2990101-2}, year = {1991}, month = {jul}, publisher = {Elsevier {BV}}, volume = {32}, number = {2}, pages = {211--222}, author = {C. Wrathall}, title = {Trace monoids with some invertible generators: two decision problems}, journal = {Discrete Applied Mathematics} }