let
datatype 'a rt = recrt of ('a rt) -> 'a;

fun Y G   = let fun Ggg (recrt g) n = G(g (recrt g))n
            in Ggg (recrt Ggg)
            end;

fun F f n = if n=0 then 1 else n*f(n-1);

in

Y F 3

end
(* fixed-point combinator, suitable for (strict) SML *)
(* L.Allison, Dept Comp Sci, Monash, .au. c1988      *)