In search algorithms the open list is tothe (usually ordered) list of nodes that still need to be explored. The basic breadth-first and depth-first search simply take nodes in turn from the front of the open list to explore next, they differ only in whether the children of nodes that are explored are added to the front or end of the open list. More sophisticated algorithms (such as A*) may use more complex rules to decide which item to take next from the open list, often using {{heuristics} to guide the choice. Graph search algorithms often also require a closed list recording the nodes that have already been considered.
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