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# Jetan, Barsoom's Game of Chess

In his book, The Chessmen of Mars, the fifth book in his Martian series, Edgar Rice Burroughs, familiar to many as the author of Tarzan of the Apes and its sequels, described a game similar to chess which was played on the Mars of his stories.

The board for that game is arranged as below, following my general practice of using the symbols for conventional chess pieces wherever possible:

It is not noted whether the square in the lower left corner is Orange or Black in Jetan, and so this diagram has been left in the conventional orientation of Earthly Chess.

Although it was not made clear in the descriptions of the rules that the two Chiefs and the two Princesses stood on the same file, rather than each player's Princess being on the right of that player's Chief from his own point of view, the game played in Manator as described in the novel establishes that the former situation was the case, I've learned from another web site about the game.

Except for the Panthan, the pieces in Jetan move either two or three steps in a move, and these steps do not have to be in the same direction. All these moves are subject to the rule that a piece can't visit a square more than once during a single move.

(Given this limitation, it seems reasonable to also assume, although this is not stated, that a piece must move the full number of squares that are given in the description of its move, instead of only making a smaller number of the steps which it is allowed.)

There are some ambiguities in the description of the rules given in that novel.

The pieces in the front row are two Thoats, represented by Knights, and eight Panthans, represented by Pawns.

The move of the Thoat consists of one orthogonal step, followed by one diagonal step. (One of the two accounts of its move gives it the ability to ignore intervening pieces. If that is the case, the order of the two steps becomes irrelevant, hence, I am inclined to go with the other alternative.) The end result of this is either a Knight's move, or a move of one orthogonal step.

The move of the Panthan is one step, either forward, or sideways, or diagonal, but not backward.

 Described this way, it is not clear if a diagonal retreating move is allowed. Since "forward" doesn't include diagonally forward (and, therefore, "backward" shouldn't include diagonally backward to be consistent), and because Panthans do not promote, I think that allowing all four diagonal moves is most likely what was intended. Since it is specifically stated that Panthans do not promote, splitting the difference by having the Panthan add the diagonally backwards move upon reaching the tenth rank - similarly to some of the piece promotions in Tsui Shogi - is not really an option, unless one is at the point of taking liberties with the rules to make a more playable game (because a Panthan that can move diagonally backwards is stronger than some of the other pieces). Of course, I do reach that point below when it comes to the rule about the Chief being captured.

The pieces in the back row are:

Warrior, Padwar, Dwar, Flier (or Odwar), Chief, Princess, Flier (or Odwar), Dwar, Padwar, and Warrior.

The Warrior's move consists of two orthogonal steps; the second one can be in the same direction as the first, or angled at 90 degrees to it. (One account of its move allows it to move diagonally as well; I think this is obviously a typographical error, and need not be considered.)

The Padwar's move consists of two diagonal steps; again, the second one can be in the same direction as the first, or angled at 90 degrees to it.

The Dwar's move consists of three orthogonal steps, in any combination of directions, subject to the restriction noted above, which applies to all the pieces, of never returning to the same square in a move.

The Flier's move consists of three diagonal steps, in any combination of directions, and it may jump over intervening pieces. (In the game played in Manator, as described in the novel, the Flier, there called an Odwar, is depicted as jumping over an intervening piece, and thus the claim advanced by some that the rules were changed along with the name to add the power of jumping over an intervening piece is untenable.)

The Chief's move consists of three steps, in any combination of directions, and each step may be orthogonal or diagonal. The game can be won by capturing the opponent's Chief with one's own Chief, but if the Chief is captured by any other piece, the game is drawn.

 This rule, although it may not sound unreasonable at first glance, has occasioned quite a bit of doubt. Thus, while many people who have tried playing Jetan have found it playable, typically they have modified the rules so that the Chief can be captured by any piece; if is captured by the opposing Chief, the game is won by the other side; otherwise, the game merely continues after the capture. It is true that since both Chiefs have the same move, it is difficult to set things up to capture an opposing Chief with one's Chief, and there is the apparent danger that a Chief could go on a rampage capturing pieces until the other side, desperately low on material, settles for a draw. However, the Chess maxim "the threat is deadlier than the execution" limits this danger. Given that a Chief capturing a Chief wins the game, any piece that a Chief defends is absolutely defended against the opposing Chief. Thus, the Chief should be given the defensive role of protecting all one's men that are at risk of being captured by the opposing Chief. This provides a way to gain an advantage through the tactical maneuver of making a limited offensive use of one's Chief without compromising its defensive role. There are various approaches to addressing this perceived difficulty. One would be simply to ignore this rule, and allow the game to be won through the capture of a Chief by another piece. Another that has been used is that instead of the game being drawn, it continues rather than being won if a piece other than one's Chief captures the opposing Chief. I would be inclined to suggest a way to remove the chief difficulty this rule creates, while retaining what it adds to the game as follows: The game is drawn when a piece other than the Chief takes a Chief - until that Chief has made its first capture. Some further elaboration, to also allow victory by capturing the Chief with another piece than one's own Chief when it threatens one's Princess might also be needed to provide full balance. (Of course, since it is preferable to draw rather than to lose, this additional rules change would not additionally encourage capturing the Chief in that circumstance; instead, it is intended to change what the player moving the Chief does, so that threatning the Princess with the Chief when it is liable to capture by a lesser piece is not a way to draw.)

The Princess moves three steps, diagonal or orthogonal, and in addition can ignore intervening pieces. But it cannot capture.

Capturing the opponent's Princess wins the game. The Princess, by custom, is not removed from the board when captured. (It can safely be presumed that this, rather than a Chief capturing a Chief, is the usual fashion in which a game of Jetan is won.)

The Princess may move ten squares once during a game; this move is called the escape.

Players choose which color of piece they wish to play by mutual agreement, and then whether the Orange or Black pieces move first is determined at random, the first move alternating in subsequent games without the players changing colors. (Although that either Orange or Black can move first is not explicitly stated, it is strongly implied by the description of the game in the original sources.)

There is no special rule given for stalemate, hence it is presumably a victory for the player who forces stalemate. (Despite this, one computer implementation of Jetan makes stalemate a loss for the stalemating player.)

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