tailup :: (Int -> Int -> Int) -> Int -> Int -> Int -> Int
tailup(F, i, y, a) -> a                               | i > y
tailup(F, i, y, a) -> tailup(F, i + 1, y, F(i, a))    | i ≤ y

taildown :: (Int -> Int -> Int) -> Int -> Int -> Int -> Int
taildown(F, x, i, a) -> a                             | i < x
taildown(F, x, i, a) -> taildown(F, x, i - 1, F(a,i)) | i ≥ x

recup :: (Int -> Int -> Int) -> Int -> Int -> Int -> Int
recup(F, i, y, z) -> z                                | i > y
recup(F, i, y, z) -> F(recup(F, i + 1, y, z), i)      | i ≤ y

recdown :: (Int -> Int -> Int) -> Int -> Int -> Int -> Int
recdown(F, x, i, z) -> z                              | i < x
recdown(F, x, i, z) -> F(i, recdown(F, x, i - 1, z))  | i ≥ x

f :: Int -> Int -> Int
f(x, y) -> x | x > 100000

g :: Int -> Int -> Int
g(x, y) -> x | x > 100000