A Solution to the GHI Problem for Best-First Search

In a search graph the node's value is dependent on the path leading to it. Different paths may lead to different values. Hence, it is difficult to determine the value of any node unambiguously. The problem is known as the graph-history-interaction (GHI) problem. This report provides a solution for best-first search. First, we give a precise formulation of the problem. Then we review all important earlier proposals to overcome it, also for other searches than best first. Next, our solution is given in outline. The solution is implemented in a bestfirst search algorithm. Experimental results in the field of computer chess confirm the claim that the GHI problem has been solved for best-first search. 1 The GHI Problem Search algorithms are used in many domains, ranging from theorem proving to computer games. The algorithms are searching in a search space containing problem states (positions), often represented as nodes. A move which transforms a position into a new position is represented..