# Case 4: node and parent are red, uncle is black
	# this is a LRb or RLb conflict
	# we rotate the tree to balance it
	private fun insert_fixup_case4(node: N) do
		if node == node.parent.right and node.parent == node.grandparent.left then
			rotate_left(node.parent.as(not null))
			node = node.left.as(not null)
		else if node == node.parent.left and node.parent == node.grandparent.right then
			rotate_right(node.parent.as(not null))
			node = node.right.as(not null)
		end
		insert_fixup_case5(node)
	end