Korpalski Chess Variant

A minimalist definition of Korpalski Chess

  1. Korpalski Chess uses a standard chessboard.
  2. Korpalski Chess uses a standard set of chessmen.
  3. Each chessman can be in three distinct states:
    • occupy a square on the chessboard
    • belong to the reserve beside the chessboard
    • belong to the prison of captured pieces beside the chessboard
  4. The game starts with an empty chessboard and all the 32 chessmen in the reserve.
  5. White makes the first move by placing the White king on the empty chessboard, then Black places the Black king so that the two lone kings form a legal chess position.
  6. The players make moves in turns. White can move White chessmen on the board or use White chessmen from the reserve. Black can move Black chessmen on the board or use Black chessmen from the reserve.
  7. There are two kinds of moves:
    • a legal standard chess move on the chessboard
    • the placing of a chessman from the reserve on an empty square
  8. The legal standard chess moves are restricted in two ways:
  9. There is no castling.
  10. A pawn can be promoted only to a captured chessman in the prison.
  11. The notion of check is identical as in standard chess:
    to determine if a king is under check we focus only on the position on the chessboard and treat it like standard chess.
  12. After a move with a chessman from the reserve no king can be under check.
  13. It is illegal to place pawns on the first and eighth row.
  14. Checkmate is a situation when a king is under check and no legal Korpalski Chess move is possible.
  15. Stalemate is a situation when a king is not under check and no legal Korpalski Chess move is possible.
  16. Checkmate wins the game.
  17. Stalemate is a draw.
  18. A draw is achieved by having the exact same position for the third time, which includes the side to move and the chessmen outside the board.
  19. When all pawns have been captured and there are no pieces in the reserve the game reduces to standard chess and all chess rules apply.

Important facts about Korpalski Chess that follow from the rules above

The usual 32 chessmen are sufficient to play the game

This is not true in standard chess where pawns can be promoted to any piece without restrictions allowing for example nine queens of the same color.

In Korpalski Chess the same set of 32 standard chessmen is used throughout the game with the chessmen switching states between reserve, chessboard, prison, and sometimes they simply disappear from the game: Each chessman can be in four distinct states: Note that a captured pawn cannot return to the game. Theoretically, it can be considered to belong to the prison to simplify the rules into three distinct states, but in practice captured pawns simply disappear from the game. Moreover, the pieces in the prison can only return to the chessboard due to pawn promotion. Hence with all White pawns captured all White pieces in the prison disappear from the game.

The notion of check is tricky when pawns are one square close to promotion

The notion of check is identical as in standard chess: to determine if a king is under check we focus only on the position on the chessboard and treat it like standard chess.

With no White pieces in the prison a White pawn on the 7th rank cannot make a legal move. However, it is still considered to attack the opponent's king diagonally for the purpose of determining check. The Black king cannot enter into check from such an immobile pawn. Moreover, it is not legal to place a pawn from the reserve on the 7th rank if it would check the king in standard chess.

How the game ends

Checkmate is a situation when a king is under check and no legal Korpalski Chess move is possible. While check is identical in standard chess and Korpalski Chess, a checkmated king in terms of standard chess can still be defended from check by placing a piece from the reserve between the king and the checking piece.

Stalemate is a situation when a king is not under check and no legal Korpalski Chess move is possible. Similarly, a stalemate in standard chess is not considered stalemate in Korpalski Chess if the side to move can place a piece from the reserve on the chessboard.

Checkmate is the only way to win and there are several ways for the game to end in a draw.

There are many ways for the game to end in a draw after it reduces to standard chess when all pawns have been captured and there are no pieces in the reserve. In particular, insufficient mating material.

However, it should be left for the community to decide how to treat the 50 moves rule in Korpalski Chess. These endgames may involve complicated positions with many pieces and no pawns. Perhaps it makes sense to suspend the 50 moves rule here.