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Tandem Chess. 4 player variant where pieces taken from your opponent are given to your partner. (2x(8x8), Cells: 128) (Recognized!)[All Comments] [Add Comment or Rating]
H. G. Muller wrote on Tue, Oct 22, 2019 09:49 AM UTC:

I am a bit worried about this paragraph that states a dropped Rook is considered virgin (and thus fit for castling). As far as I know there doesn't exist any on-line server that uses this rule, or any engine that plays by this rule. It is also a very weird rule: when you move a Rook you lose castling rights, and moving it back to a corner normally doesn't restore them. And a drop move is a move like any other.


Kevin Pacey wrote on Wed, Oct 23, 2019 02:38 AM UTC:

Oddly the wikipedia entry for Bughouse Chess (which is given there as synonymous to Tandem Chess or Siamese Chess, unlike in CVP's entry for Bughouse plus Tandem Chess [which notes some differences in rules between the two variants]) does not appear to discuss drops of captured rooks at all, unless I missed it:

https://en.wikipedia.org/wiki/Bughouse_chess


Cagliostro's Chess. Variant on 12 by 8 board with combination pieces. (12x8, Cells: 96) [All Comments] [Add Comment or Rating]
Kevin Pacey wrote on Fri, Nov 1, 2019 03:12 AM UTC:

Does anyone know if this variant has been tested much over-the-board or online? Superficially, it looks like if a player castled (especially kingside, with the enemy queen beaming in to the l-pawn's home square right from the setup), he might routinely get destroyed by an attack based almost on long diagonals alone. In any case, the opposing bishops are beaming at each other's home squares in the setup, which may be seen as undesirable (though for 12x8 variants with the inclusion of bishops, some sort of tradeoff(s) may always have to be made when it comes to choosing a setup).


Yalta. A three player chess variant. (Cells: 96) [All Comments] [Add Comment or Rating]
Colin Rowat wrote on Sat, Nov 9, 2019 12:12 PM UTC:
  1. how does Yalta compare to other three-player chess variants?  (I'd come across it as a teen, so have a soft spot for it.  It also looks like a more direct extension of two-player chess than some others that I've seen - which I also like.)
  2. is there anyone who makes Yalta chess mats?

Marseillais Chess. Move twice per turn. (8x8, Cells: 64) (Recognized!)[All Comments] [Add Comment or Rating]
🕸Fergus Duniho wrote on Mon, Nov 11, 2019 02:28 AM UTC:

While fixing a bug in the Game Courier code, I came across a situation that is not clearly covered by the rules. Suppose a Pawn makes its usual first-move double move, then it moves forward one more space on the same turn, so that it moves a total of three spaces forward. Can it be captured by en passant if the opponent has a Pawn in the usual position? On the one hand, it has made a double move, and a Pawn that makes a double move can normally be captured by en passant. On the other hand, it is no longer on the space it moved to when making its double move, and if the player had wanted to, he could have moved the Pawn forward one space, then captured the Pawn that was in a position to capture it by en passant if it had made a double move.

For now, I have written the code to forbid en passant capture in this situation. Does anyone know if there is any precedent for allowing en passant capture in this situation?


Greg Strong wrote on Mon, Nov 11, 2019 02:43 AM UTC:

This is tricky, and different players have used different rules.  This page states:

According to Pritchard's Popular Chess Variants, 'The en passant rule has seen change. Modern players allow it only when the Pawn advance formed the second move of a turn.'. This helps to eliminate some ambiguity discussed in the comments. (What if a player advanced a Pawn by two squares, then occupied the intermediate square with a piece?)

The situation is potentially even worse than this example.  What if a pawn made a double move and then went on to capture a piece with its second move?  Would capturing it en passant then magically bring back the piece it captured?

There was a discussion about this on the talk chess site a few years ago.  The discussion went on for quite a while and a lot of people weighed in.  I can try to dig up the thread, but the final outcome was that there is really only one interpretation of en passant makes sense and doesn't lead to problems: the en passant capture must be made with a player's first move and can only be used to capture a two-space move by the opponent's second move.  If a player makes a two-space pawn move with the first of his two moves, it is not subject to en passant.  ChessV uses this interpretation and I believe Game Courier should do the same.


H. G. Muller wrote on Mon, Nov 11, 2019 08:31 AM UTC:

In any case it should be clear that you can never capture a piece after it moved away with the second move, just because it was in a location after its first move where you could capture it. It would be highly illogical if e.p. capture would be an exception to that. Whether you want a second move done with a different piece to destroy e.p. rights is a matter of choice.


🕸Fergus Duniho wrote on Mon, Nov 11, 2019 04:37 PM UTC:

I changed it to allow en passant only when the Pawn's double move is a player's second move, and I confirmed that this change did not break any past game. But as I was rewriting the rules, one more thing occurred to me. Suppose a Pawn's double move done on the first move puts a King in check, thereby ending the turn without a second move. If this check could not be ended with an en passant capture, this could allow a King to be checkmated in a position that would not be checkmate in Chess, and this would violate the intention behind the game.

So, I think we have to exclude the rule that en passant is allowed only when a Pawn makes a double move on the second move of the turn. This could be replaced with the rule that en passant is allowed only when the double move was the opponent's last move, or it could be replaced with the rule that en passant is allowed only when the Pawn that made a double move didn't make another move after it. For the meantime, I'll change it back to the latter.


H. G. Muller wrote on Mon, Nov 11, 2019 05:37 PM UTC:

Well, another move should clear the e.p. rights generated by any previous move. Like it always does. E.p. rights are transient, and last only to the end of the next move. (And not to the end of the next turn!)


Greg Strong wrote on Mon, Nov 11, 2019 06:57 PM UTC:

Yes, I should have said en passant only allowed if the two-space pawn move was on the player's most recent move (rather than second move) to account for this.  I just tested this situation and ChessV does allow en passant to get the king out of check.  It is implemented as H. G. suggests - any move clears the EP square.


🕸Fergus Duniho wrote on Mon, Nov 11, 2019 08:26 PM UTC:

The earliest source I can find is Pritchard's 1997 Encyclopedia, which is the source Hans originally used to write this page. It says "En passant is legal if the opponent moved a pawn two squares on either of his moves but the capture must be made at once. However, if the opponent made two two-square pawn moves, both pawns can be taken e.p. This last rule is credited to Alekhine by F. Palatz in an article on the subject (LEC Sep 1928)." LEC refers to L'Echiquier. Notably, Alekhine is not one of the inventors, and how the game should handle en passant might be something that the original inventors didn't think of. It is also unknown whether the game was invented by Fortis or by de Queylar. It has been attributed to each one, but its origins are murky.

Regarding one of the alternative rules, it says "The game was sometimes played with alternative rules: a check on the first move was illegal and a player could not capture e.p. if the pawn had been moved in the first part of the player's turn." It's very possible that Fortis and de Queylar invented similar games with slightly different rules that eventually got conflated together.

The rule that Greg Strong and H. G. Muller propose has the advantage of being the simplest to program. It works with code that has already been written for Chess. Of course, the original inventor of the game would not have had this in mind, since programming games was not an option when it was invented. However, the rules as initially described above can be programmed, and that's what I have done in Game Courier. The only issue with them is that they need emendation for a Pawn that moves twice on the same turn. If we keep those rules, then en passant capture should be impossible in this instance, or it should be allowed for the Pawn on its new space. I have the former programmed right now, whereas the latter would be trickier to program.


Greg Strong wrote on Mon, Nov 11, 2019 08:45 PM UTC:

So if the player moved a pawn two spaces and the placed a piece on the square passed over you would allow capture of both with a single move?  To me, that doesn't fit comfortably with the spirit of chess.  Pritchard notes that the rule has changed over time, probably for good reason.  Similarly, Marseillais Chess is now played in 'balanced' form because it is clearly superior.  Old games do evolve and that's a good thing.

Here is the thread on Talk Chess where this was discussed.  In it I actually started iwth Fergus' view and was persuaded to adopt my current view.


H. G. Muller wrote on Mon, Nov 11, 2019 08:49 PM UTC:

What I cannot imagine is that the original inventor would have thought it reasonable to allow e.p. capture

  1. when the capturing Pawn has not seen the other one move past it
  2. when the Pawn that moved is no longer there
  3. when the e.p. square gets occupied

🕸Fergus Duniho wrote on Tue, Nov 12, 2019 02:54 AM UTC:

So if the player moved a pawn two spaces and the placed a piece on the square passed over you would allow capture of both with a single move? 

The way it is coded, that would not happen. The first thing it checks for is an ordinary diagonal capture. If the move involves one, that's what it does, and it doesn't get around to checking for an en passant move.

I have started to look at the thread you provided a link to, and I will continue to look at it tomorrow.


🕸Fergus Duniho wrote on Tue, Nov 12, 2019 04:29 PM UTC:

What I cannot imagine is that the original inventor would have thought it reasonable to allow e.p. capture

  1. when the capturing Pawn has not seen the other one move past it
  2. when the Pawn that moved is no longer there
  3. when the e.p. square gets occupied

That's all reasonable, and what I've coded for Game Courier is in conformity with it. The first one is already handled by the rule that en passant is not allowed on the second move unless the player is making two en passant captures. This prevents a player from using his first move to move a Pawn into position to do an en passant capture. (Note that a Pawn that was already in the position to do this could just capture the double-moved Pawn normally and then use its second move to go to the space the now captured Pawn had passed over, reaching the same position without using en passant.)

The second is handled by setting the ep1 variable to false whenever a player moves the same Pawn again. Since ep1 would store the position of the previously moved Pawn if the last move were a Pawn move, it checks whether the second move is from that location.

The third is handled by checking for a normal capture before checking for other types of Pawn moves. If the move is a normal capture, it never gets to the code for en passant. If it's not a normal Pawn capture, then the move was to an empty space. By the time it reaches the elseif clause for en passant, it has already been determined that the space is empty.

 


🕸Fergus Duniho wrote on Tue, Nov 12, 2019 10:05 PM UTC:

One more issue has come up. Suppose that a player makes a first move that leaves him with no legal second move. Does this end his turn like a checking move would, or does it end the game in a draw? Pritchard says in Popular Chess Variants, "A player who is not in check and cannot complete his turn is stalemated." This suggests the latter, but he could have said it more explicitly if that is what he meant. Is there any consensus on how being unable to move on the second move should be handled?


wdtr2 wrote on Wed, Nov 13, 2019 12:29 AM UTC:

Tough Question.  I could see the 2nd move being "pass", and if Marseillas is a mandatory 2 move game per person, it is a strong arguement that it is a stalemate.  You are the programmer to the game, I would pick the one Fergus Likes, and make sure it is mentioned in the rules.


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