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
Article, 1992