4.3

parts2 [] = False

parts2 (x:xs) = (mod (length (x:xs)) 2 == 0) && (parts2' [x] [] xs)
    where
        n = div (length (x:xs)) 2
        parts2' xs ys [] = length xs == n
        parts2' (x:xs) [] (z:zs) = (try (x:xs) (z:zs)) || parts2' (x:xs) [z] zs
            where
                try (x:xs) (z:zs)
                    | length (x:xs) == n = False
                    | z > x = parts2' (z:x:xs) [] zs
                    | otherwise = False
        parts2' (x:xs) (y:ys) (z:zs) = (try1 (x:xs) (y:ys) (z:zs)) || (try2 (x:xs) (y:ys) (z:zs))
            where
                try1 (x:xs) (y:ys) (z:zs)
                    | length (x:xs) == n = False
                    | z > x = parts2' (z:x:xs) (y:ys) zs
                    | otherwise = False
                try2 (x:xs) (y:ys) (z:zs)
                    | length (y:ys) == n = False
                    | z > y = parts2' (x:xs) (z:y:ys) zs
                    | otherwise = False