-- Merges two sorted lists in ascending order to give
-- a single sorted list in ascending order, e.g.,
  -- > merge [2, 5, 6] [1, 3, 4]
  -- [1, 2, 3, 4, 5, 6]

merge :: Ord a => [a] -> [a] -> [a]
merge xs     []     = xs
merge :: Ord a => [a] -> [a] -> [a]
merge xs     []     = xs
merge xs     []     = xs