Jetan is the chess-like game played by the inhabitants of Barsoom (Mars) in the novels by Edgar Rice Burroughs (ERB). This application allows two people to play each other at the game, and to decide which of the movement, wagering and duelling options apply to each match.
Most of the background for this project came from the web pages by Larry L. Smith (LLS). I have used his suggestions for the naming conventions and abbreviations for the pieces, the game types, and the game recording system. You should visit his page for a more in-depth analysis of the game's rules and conventions than is presented here.
Before starting the game, the players must agree on the rules to be used, and implement them with the Setup page. Once done, press [Play Mad Elf's Jetan] and the game page will be loaded. If you want to save your settings for later use, bookmark the game page.
There is a certain amount of ambiguity in ERB's description of the game. This allows the players to choose exactly how each of the pieces move; each player can choose a different set of moves if desired.
The value of some pieces depends on which options are chosen (see below), to reflect the power that the different options grant. Piece values only affect the game under certain circumstances (see below).
If both players use the Chained Chief and they start facing the opponents' Princesses, they can never land on the same square. However, as you may want to play a game where the Chief-takes-Chief option is never available, you are free to select this version.
The Princess can't have Chained Escape: where would your Princess be sitting to be able to move 10 squares in a straight line? The Setup page won't allow you to select it; it'll force it to Free or Chained Civil.
Also, you can't select a Chained (Civil or Wild) Frightened Escape. The pathfinding algorithm used for the other moves takes far too long* for these Escape versions, so the squares the direction-changing Princess escapes to can't take account of the paths used - but because she can jump, this isn't a problem unless she's Frightened. If you want a frightened Princess, use the Free Frightened Escape versions, until I can find a better algorithm.
* - as in, it never actually ran to completion during testing. Seven steps it can manage in a few seconds; ten steps takes minutes (at least!).
Jetan is a game of wagering and combat, as well as one of strategy. By leaving the Game Rule options at default, it is a pure strategy game in the same way as chess.
Normally, the pieces move for free. You can choose to require an ante (into the pot) for pieces to move: either 1 point, or the piece value. Obviously this can lead to situations where a player is incapable of moving any of hir pieces; thus a [PASS] option is available.
Normally, the piece that is moving captures the one it lands on. You can choose to have the pieces duel for possession of the square instead: either for free, or by paying the piece's value as a bounty (to be taken by the winning piece's player).
When duelling, each piece has two random numbers between 0 and 9 added to its value. The piece with the larger total wins the duel; if the totals are the same, the process is repeated. The odds for this contest are:
| Difference in Value | Chance of lower-valued piece winning | |
|---|---|---|
| 0 | 50% | |
| 1 | 43% | |
| 2 | 36% | |
| 3 | 29% | |
| 4 | 24% | |
| 5 | 18% | |
| 6 | 14% | |
| 7 | 10% | |
| 8 | 7% | |
| 9 | 5% |
If pay-to-duel is selected, and the defending piece's player can't ante its value, the attacking piece wins by default.
You can select two different kinds of ante: fixed (50), or force-based. Additionally, with a force-based ante you can choose to have captured pieces pay up their points values from the pot.
A force-based ante could be anything from (depending on the piece values) 34 to 50 at most: when a force-based ante is in use, each player will be given an opportunity to reduce hir ante by playing with some pieces missing.
When any kind of ante is in play, the application will check to make sure that both players can ante enough before starting each game. If one of them can't, the match is over, as an overall winner has been found. If both players can't ante enough, the pot is split between them and the match continues.
Unlike chess, the normal layout for Jetan is to have each player's pieces sit in the same order from their points of view (i.e. with each Chief facing the opponent's Princess). You can choose to swap Orange's Chief and Princess so the Chiefs start facing each other.
Normally, if a Chief is captured by a piece other than the opposing Chief, the game is drawn. You can choose to have the game continue in this situation.
You can win the game by any of these methods:
The game can be drawn in two ways:
At any point during the game (except when an Escape is already in progress), a player can click on hir [ESCAPE!] button, activating hir Princess' Escape move. Once the Princess has moved, the game proceeds from where it left off.
Additionally, if an enemy piece lands on a Princess' square, that Princess' Escape move is automatically triggered.
Each Princess is allowed only one Escape move per game.
I have given the pieces point values based closely on their flexibility of movement:
This gives a set of piece values close (but not identical) to the ones suggested by LLS.
For example:
For comparison's sake, here's the number of points the Chief would be worth based on moves alone:
| Chained Chief (CC): | 1* |
| Chained Civil Chief (CCC): | 4 |
| Chained Wild Chief (CWC): | 10 |
| Free Chief (FC): | 3 |
| Free Civil Chief (FCC): | 6 |
| Free Wild Chief (FWC): | 10 |
* - 0.80 actually; less than any other piece (even the Chained Padwar and Chained Warrior are worth 0.88).
As each game is set up and played out, the Game History field will fill up with a description of the initial conditions and moves. The application uses the Technical Notation suggested by LLS, with a couple of extra devices. LLS asks that you send him your game notes, as he is compiling a reference work on the game. His email address is llsmith@ev1.net.
The first entries in the game history are the timestamp, the movement, capture and ante rules selected, and a description of the piece types (and unused pieces, if any) for each side. The actual play of the game then follows.
When describing a move, the ranks are numbered 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, beginning with the Black end; the files, beginning with the southern left, are lettered A-J. A move would be of the form "G2-G3".
When duelling is turned off, the usual notation for taking a piece is used: "G2xG3".
When duelling is turned on, the notation records the winner of the duel thus: "G2-G3(B)" or "G2-G3(O)".
When a Princess is forced to Escape by a piece landing on its square, the escape move is appended to the attacking move, thus: "G2-G3eA4".
When a Princess uses its Escape move by choice, the move is noted before the current player's move, thus: "(E0eJ5) G2-G3"
When a player chooses to pass, it is recorded thus: "---"
When the game is won, the last move has "C", "P", or "X" appended, depending on whether the game was won by Chief capture, Princess capture, or repeated passing respectively.
If the game is drawn, the last move has "d" appended.
An (rather contrived) example:
Mon, 26 Jul 2004 17:55:41 GMT Move for free Pieces duel Ante by force size, captured pieces pay ransom Black's force: CPN, FW, CPW, FT, CD, CF, CCC, CCBP (FBE) (force complete) Orange's force: CPN, CW, CPW, CT, FD, FF, CCC, CCBP (FBE) (missing B9, C9, H9, I9) 1. G1-H4 J9-I7 2. D1-C4 A9-B7 3. H2-G3 G0-J7 4. I1-I3 C0-C7 5. C4-F7 C7-F7(O) 6. H4-I7(B) B7-C5 7. I3-G5 D0-C7 8. G5-E7 J7-G4 9. E7-C5(O) C5-E4 10. J2-I4 G4-F1eJ5 11. I7-F8 (E0eG0) E9-F8(B) 12. H1-H4 F1-I4(O) 13. H4-I4(B) E4-G3(B) 14. E1-H1 F7-F4 15. H1-H4 F4-H5 16. J5-J2 H5-J4 17. I4-J4(O) J4-J2 P
This Jetan simulator is ©2004 Mad Elf. Users are free to make and distribute copies of this work, as long as (a) no changes are made to any part of it or its subsidiary files, and (b) no charge or fee of any kind is imposed on such distribution. Users are free to make 'fair use' of this work by exploiting its methodology, algorithms, and formatting tricks in works of their own.
This simulator can be downloaded from Mad Elf's Software Page.