append :: Node a -> Node a -> Node a
append (Node s1 n1) (Node s2 n2) = Node (s1+s2) (n1 V.++ n2)
append :: Node a -> Node a -> Node a
append (Node s1 n1) (Node s2 n2) = Node (s1+s2) (n1 V.++ n2)
append (Node s1 n1) (Node s2 n2) = Node (s1+s2) (n1 V.++ n2)