"The Prisoner's Dilemma" is played on a symmetrical 84 square board. The center area is 7x7, with an empty "Black Hole" in the middle where the center square would be. This is not a square (ideally, the board would be thick vertically and this hole would be a place to drop all captured pieces, which would roll down into a storage compartment beneath the board). A small nine-square isosceles "triangle" is appended to the center of each side, with the longest side facing the center of the board (See diagram).
The Pieces: Players begin with 20 pieces apiece:
They are arrayed in two sections - the Army, which is nearest to the player as he sits at the board, and the Royal Court.
These pieces behave as in orthodox (FIDE) chess, with the following
- The Guard moves one square orthogonally (up, down, left, or right) but not diagonally. It cannot leave its Royal Court, it cannot be capture, and it cannot capture any piece, except for the enemy Prisoner. After 40 moves, the Guards earn a "promotion" and instantly transform into Knights, which are allowed to venture outside the Royal Court. If a King is checked by this transformation, it is considered to be a "checkmate" move and play proceeds accordingly (see Rules).
- The Prisoner moves like a King, and can capture only undefended enemy pieces; however, a Prisoner cannot capture the uncapturable Guard or the opponent's Prisoner (thus, two prisoners side by side are actually NOT attacking each other). The Prisoner is a semi-royal piece; if it is attacked, it must be moved, and it cannot move to a square where it is under attack. Unlike other pieces, if the Prisoner is captured, it is returned to its starting square (g0 or g12).
- The elephant can move either 2 or 3 spaces orthogonally, but only towards enemy territory, never backwards. However, it has some movement restrictions: one, its destination square must be empty; two, it cannot advance if a Prisoner or Elephant blocks its move (thus, Elephants cannot capture other Elephants or the Prisoner); and three, it demolishes any piece between where its beginning and ending squares on a particular move - including a player's own. If an Elephant lands on a square on the edge of the board (a6, b5, b7, c4, c8, g0, g12, h1, h11, etc.), it immediately dies of exhaustion and is removed from the board. However, anything it demolished on that turn remains destroyed.
- Pawns do have an initial double-move option as in orthodox chess, except on the F and H files (where the pawns are advanced one square). The difference is promotion. A pawn promotes when it can no longer advance. Pawns on g5 and g7 do not promote on those squares, as they could, theoretically, advance into the Black Hole. Pawns may promote as follows:
In files A, B, C, M, N, and P, to bishop or knight only; in files D, E, J, and K, to rook, bishop, or knight; and in files F, G, and H, to queen, rook, bishop, or knight. Pawns cannot promote to pawn, elephant, king, or prisoner.
The Object: Each player must complete two objectives to win. The primary objective is the capture of the opponent's King, accomplished via checkmate as defined in orthodox chess. The second objective is to return the Prisoner from enemy territory into the "Royal Court," the "triangle" of nine squares at the edge of the board in which the player's own King began. If each player accomplishes only one of his objectives, the game ends in a draw (for example, it is a draw if one player captures the opponent's King, but the opponent's Prisoner safely returns to the correct Royal Court).
The Rules: White goes first; each player makes one move per turn, except as
outlined in the following special circumstances/conditions:
- There is no castling move.
- If a King is checkmated, the checkmated player forfeits one turn, and the player administering checkmate must make a move which captures the King as if it were a non-royal piece. Play then continues normally.
- If a player's King and Prisoner are both attacked simultaneously, the King must be saved, if possible. The attacking player is not required to capture the Prisoner on the subsequent move. If a player's King cannot be saved (i.e., it is checkmated), he forfeits his move, and his opponent must make a move which captures the King. If the Prisoner remains attacked after this move, the Prisoner must be moved out of check if possible.
- It is a legal move for any piece to jump into the Black Hole as if it were a square. If this happens, that piece is destroyed. If a Prisoner jumps into the Black Hole, he dies, and that player loses instantly. No piece may make a move passing through the Black Hole, however, Bishops may move diagonally from f6 to g7, g7 to h6, etc., and Knights may "leap" the Black Hole, for example, f5 to h6.
- If a player has no legal moves (stalemate), the game is a draw. Other drawing conditions are: by mutual agreement; by 100 consecutive moves without a pawn move or piece capture; by perpetual check or perpetual attack on the Prisoner; by the same position being repeated three times; or by both players being unable to win the game (e.g., insufficient mating material).
Algebraic notation is used to document a game. The files are denoted, from left to right from White's perspective, a through p; the letters I, L, and O are omitted because they would be confusing. Standard FIDE notation applies for pawn moves: for example, "e4" denotes pawn to e4. Bj6 denotes Bishop to j6, Qh10 denotes Queen to h10, etc. Elephants have a special notation when they make a capturing (demolishing) move. For example, Eh6 (xj6) denotes an enemy piece destroyed on j6. Eh6 (Xj6) denotes a friendly piece destroyed on j6. Eh6 (Xj6, xk6) denotes a friendly piece destroyed on j6 and an enemy piece destroyed on k6.