fixpoint :: (X->X)->X
fixpoint = /*magic*/

f :: Int -> Int
f x = x * 2
print (fixpoint f) // prints "0"

g :: String -> String
g s = "Hello, " ++ s
print (fixpoint f) // error, no fixed point

foo :: (nat->nat)->(nat->nat)
foo f =
	\n -> if n == 0 then 1 else n * f (n - 1)

bar :: nat->nat
bar = fixpoint foo //????
	//actually, bar is a function computing factorial