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Solving chess

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   Finding an optimal strategy for playing chess

   Solving chess means finding an optimal strategy for the game of chess,
   that is, one by which one of the players (White or Black) can always
   force a victory, or either can force a draw (see solved game). It also
   means more generally solving chess-like games (i.e. combinatorial games
   of perfect information), such as Capablanca chess and infinite chess.
   According to Zermelo's theorem, a determinable optimal strategy must
   exist for chess and chess-like games.

   In a weaker sense, solving chess may refer to proving which one of the
   three possible outcomes (White wins; Black wins; draw) is the result of
   two perfect players, without necessarily revealing the optimal strategy
   itself (see indirect proof).^[1]

   No complete solution for chess in either of the two senses is known,
   nor is it expected that chess will be solved in the near future. There
   is disagreement on whether the current exponential growth of computing
   power will continue long enough to someday allow for solving it by
   "brute force", i.e. by checking all possibilities.

   Progress to date is extremely limited; there are tablebases of perfect
   endgame play with a small number of pieces, and several reduced
   chess-like variants have been solved at least weakly. Calculated
   estimates of game tree complexity and state-space complexity of chess
   exist which provide a bird's eye view of the computational effort that
   might be required to solve the game.
   [ ]


     * 1 Partial results
          + 1.1 Endgame tablebases
          + 1.2 Chess variants
     * 2 The complexity of chess
     * 3 Predictions on when or if chess will be solved
     * 4 See also
     * 5 References
     * 6 External links

Partial results[edit]

Endgame tablebases[edit]

     a b c d e f g h
   a7 black rook
   h7 black knight
   c6 white queen
   f4 black king
   d3 white king
   h2 white knight
   d1 black bishop
   h1 black queen
   7                 7
   6                 6
   5                 5
   4                 4
   3                 3
   2                 2
   1 1
     a b c d e f g h
   A mate-in-546 position found in the Lomonosov 7-piece tablebase. White
   to move. (In this example an 8th piece is added with a trivial
   first-move capture.)

   Endgame tablebases are computerized databases that contains
   precalculated exhaustive analysis positions with small numbers of
   pieces remaining on the board. Tablebases have solved chess to a
   limited degree, determining perfect play in a number of endgames,
   including all non-trivial endgames with no more than seven pieces or
   pawns (including the two kings).^[2]

   One consequence of developing the seven-piece endgame tablebase is that
   many interesting theoretical chess endings have been found. One example
   is a "mate-in-546" position, which with perfect play is a forced
   checkmate in 546 moves, ignoring the 50-move rule.^[3] Such a position
   is beyond the ability of any human to solve, and no chess engine plays
   it correctly, either, without access to the tablebase.

Chess variants[edit]

   A variant first described by Shannon provides an argument about the
   game-theoretic value of chess: he proposes allowing the move of "pass".
   In this variant, it is provable with a strategy stealing argument that
   the first player has at least a draw thus: if the first player has a
   winning move, let him play it, else pass. The second player now faces
   the same situation owing to the mirror image symmetry of the board: if
   the first player had no winning move in the first instance, the second
   player has none now. Therefore the second player can at best draw, and
   the first player can at least draw, so a perfect game results in the
   first player winning or drawing.^[4]

   Some chess variants which are simpler than chess have been solved. A
   winning strategy for black in Maharajah and the Sepoys can be easily
   memorised. The 5 *5 Gardner's Minichess variant has been weakly solved
   as a draw.^[5] Although Losing chess is played on an 8x8 board, its
   forced capture rule greatly limits its complexity and a computational
   analysis managed to weakly solve this variant as a win for white.^[6]

   The prospect of solving individual, specific, chess-like games becomes
   more difficult as the board-size is increased, such as in large chess
   variants, and infinite chess.^[7]

The complexity of chess[edit]

   Information theorist Claude Shannon in 1950 outlined a theoretical
   procedure for playing a perfect game (i.e. solving chess):

     "With chess it is possible, in principle, to play a perfect game or
     construct a machine to do so as follows: One considers in a given
     position all possible moves, then all moves for the opponent, etc.,
     to the end of the game (in each variation). The end must occur, by
     the rules of the games after a finite number of moves (remembering
     the 50 move drawing rule). Each of these variations ends in win,
     loss or draw. By working backward from the end one can determine
     whether there is a forced win, the position is a draw or is lost."

   Shannon then went on to estimate that solving chess according to that
   procedure would require comparing some 10^120 possible game variations,
   or having a "dictionary" denoting an optimal move for each of the
   approximately 10^43 possible board positions (currently known to be
   about 5x10^44 ^[8]).^[4] The number of mathematical operations required
   to solve chess, however, may be significantly different than the number
   of operations required to produce the entire game-tree of chess. In
   particular, if White has a forced win, only a subset of the game-tree
   would require evaluation to confirm that a forced-win exists (i.e. with
   no refutations from Black). Furthermore, Shannon's calculation for the
   complexity of chess assumes an average game length of 40 moves, but
   there is no mathematical basis to say that a forced win by either side
   would have any relation to this game length. Indeed, some expertly
   played games (grandmaster-level play) have been as short as 16 moves.
   For these reasons, mathematicians and game theorists have been
   reluctant to categorically state that solving chess is an intractable

Predictions on when or if chess will be solved[edit]

   In 1950, Shannon calculated, based on a game tree complexity of 10^120
   and a computer operating at one megahertz (a big stretch at that time:
   the UNIVAC 1 introduced in 1951 could perform ~2000 operations per
   second or 2 kilohertz) that could evaluate a terminal node in 1
   microsecond would take 10^90 years to make its first move. Solving
   chess would therefore seem beyond any possible technology at that time.

   Hans-Joachim Bremermann, a professor of mathematics and biophysics at
   the University of California at Berkeley, further argued in a 1965
   paper that the "speed, memory, and processing capacity of any possible
   future computer equipment are limited by specific physical barriers:
   the light barrier, the quantum barrier, and the thermodynamical
   barrier. These limitations imply, for example, that no computer,
   however constructed, will ever be able to examine the entire tree of
   possible move sequences of the game of chess." Nonetheless, Bremermann
   did not foreclose the possibility that a computer would someday be able
   to solve chess. He wrote, "In order to have a computer play a perfect
   or nearly perfect game, it will be necessary either to analyze the game
   completely ... or to analyze the game in an approximate way and combine
   this with a limited amount of tree searching. ... A theoretical
   understanding of such heuristic programming, however, is still very
   much wanting."^[10]

   Recent scientific advances have not significantly changed these
   assessments. The game of checkers was (weakly) solved in 2007,^[11] but
   it has roughly the square root of the number of positions in chess.
   Jonathan Schaeffer, the scientist who led the effort, said a
   breakthrough such as quantum computing would be needed before solving
   chess could even be attempted, but he does not rule out the
   possibility, saying that the one thing he learned from his 16-year
   effort of solving checkers "is to never underestimate the advances in

See also[edit]

     * Shannon number (a calculation of the lower bound of the game-tree
       complexity of chess)
     * First-move advantage in chess


    1. ^ Allis, V. (1994). "PhD thesis: Searching for Solutions in Games
       and Artificial Intelligence" (PDF). Department of Computer Science.
       University of Limburg. Retrieved 2012-07-14.
    2. ^ "Lomonosov Tablebases". Retrieved 2013-04-24.
    3. ^ "Who wins from this puzzle?" A mate-in-546 chess position, with
       discussion (Post 1: Position, Post 7: Playable).
    4. ^ ^a ^b ^c Shannon, C. (March 1950). "Programming a Computer for
       Playing Chess" (PDF). Philosophical Magazine. 7. 41 (314). Archived
       (PDF) from the original on 2010-07-06. Retrieved 2008-06-27.
    5. ^ Mhalla, Mehdi; Prost, Frederic (2013-07-26). "Gardner's Minichess
       Variant is solved". arXiv:1307.7118 [cs.GT].
    6. ^ Watkins, Mark. "Losing Chess: 1. e3 wins for White" (PDF).
    7. ^ Aviezri Fraenkel; D. Lichtenstein (1981), "Computing a perfect
       strategy for n *n chess requires time exponential in n", J. Combin.
       Theory Ser. A, 31 (2): 199-214, doi:10.1016/0097-3165(81)90016-9
    8. ^ John Tromp (2021). "Chess Position Ranking". GitHub.
    9. ^ http://www.chessgames.com Magnus Carlsen vs Viswanathlan Anand,
       King's Indian Attack: Double Fianchetto (A07), 1/2-1/2, 16 moves.
   10. ^ Bremermann, H.J. (1965). "Quantum Noise and Information". Proc.
       5th Berkeley Symp. Math. Statistics and Probability. Archived from
       the original on 2001-05-27.
   11. ^ Schaeffer, Jonathan; Burch, Neil; Bjoernsson, Yngvi; et al. (14
       September 2007). "Checkers Is Solved". Science. 317 (5844):
       1518-1522. Bibcode:2007Sci...317.1518S.
       doi:10.1126/science.1144079. PMID 17641166.
       S2CID 10274228.(subscription required)
   12. ^ Sreedhar, Suhas. "Checkers, Solved!". Spectrum.ieee.org. Archived
       from the original on 2009-03-25. Retrieved 2009-03-21.

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