# Perform left rotation on `node`
	#
	# ~~~raw
	#     N             Y
	#    / \     >     / \
	#   a   Y         N   c
	#      / \   <   / \
	#     b   c     a   b
	# ~~~
	#
	protected fun rotate_left(node: N) do
		var y = node.right
		node.right = y.left
		if y.left != null then
			y.left.parent = node
		end
		y.parent = node.parent
		if node.parent == null then
			root = y
		else if node == node.parent.left then
			node.parent.left = y
		else
			node.parent.right = y
		end
		y.left = node
		node.parent = y
	end