019642d6-1889-7792-ada8-81af6ec057bc

invert :: Tree a -> Tree a invert t = invertHelper True t where invertHelper :: Bool -> Tree a -> Tree a invertHelper True (Leaf x) = Leaf x invertHelper True (Node l r) = let l' = invertHelper True l r' = invertHelper True r in invertHelper False (Node l' r') invertHelper False (Leaf x) = Leaf x invertHelper False (Node a b) = case (a, b) of (Leaf _, Leaf _) -> Node a b (Node a1 a2, Node b1 b2) -> Node (invertHelper False (Node a1 b1)) (invertHelper False (Node a2 b2)) _ -> error "invert: non‑perfect tree encountered"