balance :: (Ord a) => RedBlackZipper a -> RedBlackZipper a
-- Case 1: focus node is the root of the tree. Paint it black.
balance (Node v _ l r, []) = (Node v Black l r, [])
balance :: (Ord a) => RedBlackZipper a -> RedBlackZipper a
balance (Node v _ l r, []) = (Node v Black l r, [])
balance (Node v _ l r, []) = (Node v Black l r, [])