@article{L_b_1970,
    doi = {10.1007/bf01967649},
    url = {https://doi.org/10.1007%2Fbf01967649},
    year = {1970},
    month = {mar},
    publisher = {Springer Science and Business Media {LLC}},
    volume = {13},
    number = {1-2},
    pages = {39--51},
    author = {M. H. Löb and S. S. Wainer},
    title = {Hierarchies of number-theoretic functions. I},
    journal = {Archiv für Mathematische Logik und Grundlagenforschung}
}

@article{L_b_1970, doi = {10.1007/bf01967649}, url = {https://doi.org/10.1007%2Fbf01967649}, year = {1970}, month = {mar}, publisher = {Springer Science and Business Media {LLC}}, volume = {13}, number = {1-2}, pages = {39--51}, author = {M. H. Löb and S. S. Wainer}, title = {Hierarchies of number-theoretic functions. I}, journal = {Archiv für Mathematische Logik und Grundlagenforschung} }