push :: [t] -> [t] -> [t]
push [] list = list
push (head:tail) list = head:push tail list

revpush :: [t] -> [t] -> [t]
revpush [] list = list
revpush (head:tail) list = revpush tail (head:list)

reverse :: [t] -> [t]
reverse list = revpush list []

data Tree t = Nil | Leaf t | Node (Tree t) t (Tree t)
instance (Show t) => Show (Tree t) where
    show (Nil)               = ""
    show (Leaf x)            = show x
    show (Node left x right) = "(" ++ show left ++ "-" ++ show x ++ "-" ++ show right ++ ")"

delete :: (Ord t) => t -> (Tree t) -> (Tree t)
delete e Nil = Nil
delete e (Leaf x)
    | e == x      = Nil
    | e /= x      = Leaf x
delete e (Node left x right)
    | e == x                 = Nil
    | e < x                  = Node (delete e left) x right
    | e > x                  = Node left x (delete e right)