main = do -- your code goes here print $isFlat [Node 1, Node 2, Node 3] print $isFlat [Node 1, Node 2, Branch [Node 3, Node 4, Node 5], Node 6] data Tree a = Node a | Branch [Tree a] isFlat :: [Tree a] -> Bool isFlat = all isNode where isNode (Node _) = True isNode _ = False