@article{AMLG_1970__13_137832,
     author = {M.H. L\"ob and S.S. Wainer},
     title = {Hierarchies of number-theoretic functions. {I.}},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {39--51},
     publisher = {mathdoc},
     volume = {13},
     year = {1970},
     zbl = {0211.31205},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1970__13_137832/}
}