biggest_sum :: [[Int]] -> [Int]
biggest_sum [xs] = xs
biggest_sum (x:xs)
    | sum x > sum (biggest_sum xs) = x
    | otherwise = biggest_sum xs



greatest :: (a -> Int) -> [a] -> a
greatest f [xs] = xs
greatest f (x:xs)
    | f x > f (greatest f xs) = x
    | otherwise = greatest f xs

is_bit :: Int -> Bool