A New Approach to Draw Detection by Move Repetition in Computer Chess
  Programming
  We will try to tackle both the theoretical and practical aspects of a very
important problem in chess programming as stated in the title of this article -
the issue of draw detection by move repetition. The standard approach that has
so far been employed in most chess programs is based on utilising positional
matrices in original and compressed format as well as on the implementation of
the so-called bitboard format.
  The new approach that we will be trying to introduce is based on using
variant strings generated by the search algorithm (searcher) during the tree
expansion in decision making. We hope to prove that this approach is more
efficient than the standard treatment of the issue, especially in positions
with few pieces (endgames). To illustrate what we have in mind a machine
language routine that implements our theoretical assumptions is attached. The
routine is part of the Axon chess program, developed by the authors. Axon, in
its current incarnation, plays chess at master strength (ca. 2400-2450 Elo,
based on both Axon vs computer programs and Axon vs human masters in over 3000
games altogether).
