Chess problem: Difference between revisions

Revision as of 14:56, 29 May 2023

Revision as of 12:01, 14 August 2023

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*'''[[Retrograde analysis|Retrograde analysis problems]]''': such problems, often also called ''retros'', 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 White's last move?", "Has the bishop on c1 moved?", "Is the black knight actually a promoted pawn?", "Can White 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 [[#Beauty in chess problems]]|Beauty in chess problems]]), the Black ones are not. A unique problem is: "Construct a game with black b-pawn checkmating on move four" (from ''Shortest construction tasks map'' in [[#External links|External links]] 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.

Across most of the above genres, there is great interest in exploring [[fairy chess]], in which non-standard boards, pieces or rules apply.