Factorial in the Lambda Calculus

Define H as follows, to represent 1 step of recursion.

Note that ISZERO, MULT, and PRED represent particular combinators that accomplish these functions.

H = (? f. ? n.(ISZERO n) 1 (MULT n (f (PRED n))))

Then we can create

FACTORIAL = Y H

= (?x . (?y. x (y y)) (?y. x (y y))) (? f. ? n.(ISZERO n) 1 (MULT n (f (PRED n))))

Reference: http://en.wikipedia.org/wiki/Y_combinator

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