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Wright, E.M and Hardy, G.H. * An Introduction to the Theory of Numbers.*

Oxford: Oxford University Press, 1938.

Chapter five, “Congruences and Residues,” provides an explanation and summary of Euler’s fuction, the mathematical basis for programming the code of *Agrippa*.

“5.5. Euler’s Function…any set of *phi*(*mu*) residues, one from each class, *is called a complete set of residues prime to mu*.” (Facsimile image of excerpted text available in Documents.)