A (haskell program representing a) lambda term whose normalization is not known

wssp.hs

sq = floor . sqrt . fromIntegral

primes = 2:filter (\n -> all (\m -> not (m `divides` n)) (cand n)) [3..]
    where cand n = takeWhile (<= sq n) primes

m `divides` n = n `mod` m == 0

fibs = 0:1:zipWith (+) fibs (tail fibs)

l5 p | p5 == 1 || p5 == 4 = 1
     | p5 == 2 || p5 == 3 = -1
    where
    p5 = p `mod` 5

-- checks whether a prime p is a Wall-Sun-Sun prime
wallSunSun p = (p^2) `divides` (fibs !! (p - l5 p))

normalizes_questionmark = head . filter wallSunSun . dropWhile (<= 5) $ primes