lambda n: int -> int =>

let fib = lambda f : (int -> int) -> int -> int =>
    \ n : int -> int =>
        if      n == 0 then 0
        else if n == 1 then 1
        else                f (n - 1) + f (n - 2)
in

let rec fix f : ((int -> int) -> int -> int) -> int -> int =
    \ x : int -> int =>
        f (fix f) x
in

fix fib n