private STNode<Key, Value> ceiling(STNode<Key, Value> x, Key key)
	{
		if (x == null)
			return null;

		int cmp = key.compareTo(x.key);
		if (cmp == 0)
			return x;
		else if (cmp > 0)
			return ceiling(x.right, key);

		STNode<Key, Value> t = ceiling(x.left, key);
		if (t != null)
			return t;
		else
			return x;
	}