comp :: (Int → Int) → (Int → Int) → Int → Int
comp(f, g, x) → f(g(x))

id :: Int -> Int
id(x) -> x

fact :: Int → (Int → Int) → Int
fact(n, k) → k(1)                         | n ≤ 0
fact(n, k) → fact(n-1, comp(k, [*](n)))   | n > 0

fact1 :: Int -> Int
fact1(n) -> fact(n, id)

fact2 :: Int → Int
fact2(n) → 1                              | n ≤ 0
fact2(n) → n * fact2(n - 1)               | n > 0