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Bibliography

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Georg Kreisel and William W. Tait, Finite definability of number-theoretic functions and parametric completeness of equational calculi, Z. Math. Logik Grundlagen Math. 7 (1961), 28-38. MR 0131975 (24:A1822)

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Julia Robinson, An introduction to hyperarithmetical functions, J. Symbolic Logic 32 (1967), 325-342. MR 0224472 (37:71)

[3]

Raphael M. Robinson, Primitive recursive functions, Bull. Amer. Math. Soc. 53 (1947), 925-942. MR 0022536 (9:221c)