@article{Wainer_1970,
    doi = {10.1007/bf01973619},
    url = {https://doi.org/10.1007%2Fbf01973619},
    year = {1970},
    month = {dec},
    publisher = {Springer Science and Business Media {LLC}},
    volume = {13},
    number = {3-4},
    pages = {136--153},
    author = {S. S. Wainer},
    title = {A classification of the ordinal recursive functions},
    journal = {Archiv für Mathematische Logik und Grundlagenforschung}
}

@article{Wainer_1970, doi = {10.1007/bf01973619}, url = {https://doi.org/10.1007%2Fbf01973619}, year = {1970}, month = {dec}, publisher = {Springer Science and Business Media {LLC}}, volume = {13}, number = {3-4}, pages = {136--153}, author = {S. S. Wainer}, title = {A classification of the ordinal recursive functions}, journal = {Archiv für Mathematische Logik und Grundlagenforschung} }