# Build a sequence of nodes from the initial node to `self`
	# ensure `result.first.parent == null and result.last == self`
	fun path: Sequence[BacktrackNode[A]]
	do
		var res = new List[BacktrackNode[A]]
		res.add(self)
		var node = parent
		while node != null do
			res.unshift(node)
			node = node.parent
		end
		return res
	end