Legality (possibility) of the initial position of a task ( etude ) - the ability to achieve the initial position of this task or etude through a series of legal (corresponding to chess rules) moves made from the initial position of a chess game. The legality of the initial position of a task or study is one of the basic formal requirements of a chess composition (see Orthodox composition , Unorthodox composition ).
Content
Definition
The requirement of legality of the initial position means that there must be a formal series of white and black moves ( evidence-based game ) [1] , leading to the initial position of the problem (etude) under consideration from the starting position of the chess game. In the initial position of the task (study), no more basic set of figures should be taken. In the evidence game, pawns on both sides are allowed to turn.
Legality does not require the correspondence of the moves of the evidence-based game of chess theory and even any meaningfulness of these moves, it is intended only to prove that the initial position of the task or etude could, in principle, arise when playing by the rules. When examining the legality of the initial position, it can be found out, in addition to the very possibility of obtaining the required position, which side the turn belongs to, whether the parties have the right to castling or taking in the aisle . This knowledge must be used in the decision. Some genres of retroanalysis also study the initial position on legality.
In fairy-tale chess , the legality of the initial position is usually not taken into account.
Evidence of Illegality of Position
| a | b | c | d | e | f | g | h | ||
| eight | eight | ||||||||
| 7 | 7 | ||||||||
| 6 | 6 | ||||||||
| five | five | ||||||||
| four | four | ||||||||
| 3 | 3 | ||||||||
| 2 | 2 | ||||||||
| one | one | ||||||||
| a | b | c | d | e | f | g | h | ||
If it is necessary to prove that the initial position of an etude or task is illegal , then this proof usually relies on a search for pieces that, in principle, based on the rules and geometry of the board, could not be in the indicated places if all the moves were made according to the rules. The presence of at least one such figure, obviously, proves the illegality of the position. The illustration on the right shows four options for obviously illegal positions (one in each of the corners of the board):
- Upper left corner. So that the bishop a8 could go into the corner, the field b7 at this moment should be empty. But the b7-pawn stands at the initial position, therefore, it did not go from the beginning of the game, that is, the b7-field was occupied during the whole game. Elephant a8 could not get into the corner - the position is illegal.
- Upper right corner. White king g8 stands under double check. Rooks check the white king independently of each other. In order to place them on the indicated fields, it took two moves, the very first of which the king was given a check. So, the white king stood at least one move on the board under the check, or went under the check, which is prohibited by the rules.
- Bottom right corner. The black king h3 stands under the checkered g2 pawn check. The pawn stands in its initial position, therefore, it did not go and could not check the king under its own power. So the king himself went under the check, which is prohibited by the rules.
- Bottom left corner. The white pawn can enter the a3 field either from the a2 field with a quiet move, or from the b2 field with the capture move. But the pawns on the fields a2 and b2 stand in their initial positions, therefore, they did not go. The a3 pawn could not come to this field, following the rules.
Literature
- Chess: Encyclopedic Dictionary / Ch. ed. A.E. Karpov . - M .: Soviet Encyclopedia , 1990. - S. 199. - 624 p. - 100,000 copies. - ISBN 5-85270-005-3 .
- Chess Composition Code (English), part I, sect. IV.
Notes
- β In the evidence-based game, the game is played in accordance with the FIDE rules . The only exception is the β 50 move rule β does not apply anywhere except retroanalysis.