@article{Baudisch_1981,
    doi = {10.1007/bf01917515},
    url = {https://doi.org/10.1007%2Fbf01917515},
    year = {1981},
    month = {mar},
    publisher = {Springer Science and Business Media {LLC}},
    volume = {38},
    number = {1-4},
    pages = {19--28},
    author = {A. Baudisch},
    title = {Subgroups of semifree groups},
    journal = {Acta Mathematica Academiae Scientiarum Hungaricae}
}

@article{Baudisch_1981, doi = {10.1007/bf01917515}, url = {https://doi.org/10.1007%2Fbf01917515}, year = {1981}, month = {mar}, publisher = {Springer Science and Business Media {LLC}}, volume = {38}, number = {1-4}, pages = {19--28}, author = {A. Baudisch}, title = {Subgroups of semifree groups}, journal = {Acta Mathematica Academiae Scientiarum Hungaricae} }