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The Factorial Function

fac(n) = n equals zero -> one
    [] n times (fac(n minus one))

Only one function satisfies specification:

graph(factorial) =
    {(zero, one), (one, one),
    (two, two), (three, six),
    ..., (i, i!), ...}


Author: Wolfgang Schreiner
Last Modification: November 5, 1997

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