Chess problem: Difference between revisions

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A '''chess problem''', also called a '''chess composition''', is a [[Chess puzzle|puzzle]] set by the composer using [[chess piece]]s on a [[chess]] board, which presents the solver with a particular task. For instance, a position may be given with the instruction that White is to move first, and [[checkmate]] Black in two moves against any possible defence. A chess problem fundamentally differs from over-the-board play in that the latter involves a struggle between blackBlack and whiteWhite, whereas the former involves a competition between the composer and the solver. Most positions which occur in a chess problem are 'unrealistic' in the sense that they are very unlikely to occur in over-the-board play.<ref name=oz>{{Cite web|url=http://www.ozproblems.com/home|title=OzProblems - Australian chess problem composition|website=www.ozproblems.com}}</ref> There is a good deal of [[Glossary of chess problems|specialized jargon used in connection with chess problems]].

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Of far greater relation to standard chess problems, however, are the following, which have a rich history and have been revisited many times, with magazines, books and prizes dedicated to them:

*'''[[Retrograde analysis|Retrograde analysis problems]]''': such problems, often also called <em>retros</em>, typically present the solver with a diagram position and a question. In order to answer the question, the solver must work out the history of the position, that is, must work backwards from the given position to the previous move or moves that have been played.<ref>{{cite book |author=Smullyan, R. |year=1994 |title=Chess Mysteries of Sherlock Holmes: Fifty tantalizing problems of chess detection |publisher=Random House |series=Puzzles & Games |ISBN=978-0-8129-2389-6}}</ref> A problem employing retrograde analysis may, for example, present a position and ask questions like "What was whiteWhite's last move?", "Has the bishop on c1 moved?", "Is the black knight actually a promoted pawn?", "Can whiteWhite castle?", etc. Some retrograde analysis may also have to be employed in more conventional problems (directmates and so on) to determine, for example, whether an ''en passant'' pawn capture or castling is possible. The most important subset of retro problems are:

**'''[[Proof game|Shortest proof game]]s''': the solver is given a position and must construct a game, starting from the normal game array, which ends in that position. The two sides cooperate to reach the position, but all moves must be legal. Usually the number of moves required to reach the position is given, though sometimes the task is simply to reach the given position in the smallest number of moves.

*'''Construction tasks''': no diagram is given in construction tasks; instead, the aim is to construct a game or position with certain features. For example, [[Sam Loyd]] devised the problem: "Construct a game which ends with black delivering discovered checkmate on move four" (published in ''Le Sphinx'', 1866 – the solution is 1.f3 e5 2.Kf2 h5 3.Kg3 h4+ 4.Kg4 d5#); while all White moves are unique (see <em>Beauty in chess problems</em> below), the Black ones are not. A unique problem is: "Construct a game with black b-pawn checkmating on move four" (from <em>Shortest construction tasks map</em> in <em>External links</em> section; the unique solution is 1.d4 c6 2.Kd2 Qa5+ 3.Kd3 Qa3+ 4.Kc4 b5#). Some construction tasks ask for a maximum or minimum number of effects to be arranged, for example a game with the maximum possible number of consecutive discovered checks, or a position in which all sixteen pieces control the minimum number of squares. A special class are games uniquely determined by their last move like "3...Rxe5+" or "4...b5#" from above.