Depth first, breadth first, and branch and bound are three out of many possible search strategies. A search strategy is simply a set of rules for deciding the order in which the tree is to be searched. The best order is dictated by the nature of the problem in hand, as we have seen from the examples so far. Depth-first search makes no sense for the route finder, as it entails following some arbitrarily chosen route as far as possible to see if it leads to the destination. Likewise, branch and bound is inappropriate for the jigsaw puzzle, since there is no need to keep track of other branches in the tree while we check whether the present one leads to a solution.