The Countermove Heuristic

A new move-ordering method is introduced: the countermove heuristic. It shows similarities with some previously described techniques, but differs sufficiently for a test of its-effectiveness to be undertaken. The technique is based on the assumption that many moves have a "natural' response, irrespective of the actual position in which the moves occur.Results of the use of the countermove heuristic are given and compared with similar results when using some other techniques. It appears that the countermove heuristic yields some 20% reduction in computation time for single positions. When used in game fragments, this reduction may even rise to some 50%, depending on nominal search depth. The countermove heuristic therefore seems to be a valuable element in move ordering.