let rec fact = lambda n. if n=0 then 1 else n*fact(n-1) in fact 10 {\fB Factorial. \fP}
The factorial function can also be evaluated using the paradoxical operator Y as described in an earlier section.
let Y = lambda G. (lambda g. G(g g)) (lambda g. G(g g)) in let F = lambda f. lambda n. if n=0 then 1 else n*f(n-1) in Y F 10 {\fB Factorial via Y \fP}