6.034 Artificial Intelligence - Recitations, fall 2004 online slides on search
	Avoiding Repeated States Do not return to the parent state (e.g., in 8 puzzle problem, do not allow the Up move right after a Down move) Do not create solution paths with cycles Do not generate any repeated states (need to store and check a potentially large number of states) This is done by keeping a list of "expanded states" i.e., states whose daughters have already been put on the enqueued list. This entails removing states from the "enqueued list" and placing them on an "expanded list" (In the standard algorithm literature, the list of expanded states is called the "closed list ", thus, we would move states from the open list to the closed list)