grenv: No dissent here, it is exactly what I meant.  

Justaminute: But then it is very possible the third check occurs in the same time as the third repetition of the position.  

Justaminute: There is no rule about repetition of moves in chess, only about three repetitions of the same position.

rabbitoid: You are right of course, I had forgotten about that ! A word in the rules wouldn't hurt though.  

ughaibu: The obvious answer is that the same position with a different number of checks given beforehand is in fact not the same position, so the repetition rule should not apply. Good question though since it is unclear whether the written rules mean that, and whether the implementation matches that. 

Justaminute: You are right, there are basically two ways to solve such questions.

1) Defining what is meant by check and checkmate in every new variant (even in Loop Chess, you will want to make clear that a ortho-checkmate from a distance can by parried by dropping a piece).

2) Going back to the axioms and work out what chess really means by check and checkmate, then keep those axioms as they are in every new variant bar some exceptions (three-check chess would be one).

I am not saying that 1) is stupid. Actually it is the way things are most often done. But even if you want every variant to include a (generally redundant) part about check and checkmate in its rules, it doesn't hurt to know that there is a default value given by 2).

Bwild:

Justaminute: I don't see any reason to rewrite the FIDE rules.

Actually there is one. The FIDE rules are ambiguous when it comes to variants. When is a king "under attack" ? If I am playing my king in contact of the opponent's queen, but some extra rule forbids the queen to take my king (e.g. at that move my opponent is forced to move a knight), then is my king under attack or not ? If you would answer yes, I would argue that you are falling for an optical illusion.

Conversely, if my king is safe orthochess-wise, but can be captured through the way pieces are captured in that variant (for instance, in Atomic Chess, by an explosion), is my king under attack ?

grenv & Justaminute: You are correct that the king must be attacked and that I forgot to tell about stalemate. If the stalemate rule is needed, what about "When you don't have any move that would not lose the king, you are allowed to pass your turn, and if the opponent doesn't capture your king immediately the game is a draw" ?

I can't tell about the specifics of Ice Age Chess and I agree that the fair way to tell would be to ask the inventor, but IMHO DarwinKoala has the right line of thought. A mate is not a mate if you can't actually take the king at the next move.

For an extreme example, consider a hypothetical variant where the queen is not allowed to move a single square (to make a king's move). You play 1.e4, 2.Bc4, 3.Qf3, 4.Qxf7. It would sound odd to claim that it is a mate because it would be a mate in orthochess, wouldn't it ?

As for the unwanted possibility of a king "moving into check", I think it is playing with words. If a king can't be taken at the next move, then its "moving into check" is just a potent optical illusion.

It is always possible to decide otherwise, but I think that in general variant design, playing up to the capture of the king should be the default.

Constellation36: No need to message me, I still read that forum ! Questioning the promotion rule in Ambiguous Chess sounds very valid to me, since it is an important part of the game and I adopted it only after switching back and forth.

At first I didn't even think about it : I had "normal" promotions, i.e. by the piece owner. But a friend made me notice that it was not very consistent with the variant : the opponent is supposed to choose between all moves leading to the same square, the different promotions are (in my view) different moves leading to the same square, so the opponent should be able to choose the promoted piece.

That is for the logic, but then one must see how it plays in practice. That it weakens promotion combinations in the middlegame proved to be of almost no concern. Ambiguous Chess has its share of surprising combinations (especially but not only mating attacks), and frankly I don't think it needs queen promotions in order to spice the tactics.

The endgames are another story though. True enough, promotions chosen by the opponent make a material advantage a lot tougher to convert. A pawn is already more difficult than usual to lead to promotion, and then with the current rules, achieving the promotion is far from putting an end to the game.

I was afraid that it would make most endgames draws, in which case my promotion rule would be a bad one. I don't think that it is the case. Due to abandoning the stalemate rule, almost all pieces-only endgames that are wins in Standard Chess are still wins in Ambiguous. Did you know that even two same-colored bishop were enough to win against a bare king ? I think it makes the future of a material advantage look less bleak.

So unless my assessment of the endgame winnability is wrong, it comes down to a matter of taste. Should one have lengthier endgames, when the result might be the same, except a faster one, with the normal rules ? I like endgames, so I was tempted to answer yes, but I tried not to make my personal tastes account for too much in the balance. In the end, "all other things being almost equal", I just prefered to stick with the more logical and compact ruleset.

If you still can't stand the absence of queen promotions, check the two last diagrams of the following article : http://www.brainrook.com/archives/26-Just-one-more-chess-variant.html#extended

Key McKinnis: Because the inventor thought it would be better this way, but he changed his mind since. I asked Fencer if he could restore the promotion, but he wasn't convinced (and he doesn't like rule changes). I have played Recycle Chess with promotions and I liked it much better that way.

ughaibu: Probably it is thought that because otherwise one of the knights would often be dedicated to the defensive task of enhancing the movement of its king, making the play less dynamic. But I didn't try it that way.

By the way, without the restriction about knights it might be unclear whether a knight connected with its colleague could capture a piece.

Karthum: 1 is interesting. I suppose that it would be allowed to pick a pinned piece (which makes a triple check possible).

2 is sometimes played but is widely disapproved by the community of Bughouse (= 4-players) and Crazyhouse (=Loop Chess) players as a beginner's rule. It does not enhance the tactics, just makes them more artificial - like instead of mating by dropping a line piece 1 away from the king, dropping a line piece 2 away from the king, the opp blocks, take the blocking piece with mate.

rabbitoid: A great idea. With your game, one will get the feeling of living without the tedious effort of thinking. I wonder whether WhisperzQ's suggestion wouldn't cut off some of the playing thrill though :-)

Fencer: Fine then. The ECV doesn't give more details, but I like it the way the rules are.

coan.net: Then our memories do agree. It would be worth to check which way the rules were implemented - and which way they should, which is not obvious. I'll see if the Encyclopedia of Chess Variants is more precise than the chessvariants.com entry.

Fencer: Are you sure ? In that position : Échecs du Chat de Chester (mangue contre nabla) , my remembrance is that the system did not let me play e5xd4, which I interpreted as normal since the pawn was pinned by the enemy king (my king would be in check by the other king). But if what you say is true, e5xd4 would have been a perfectly valid move.

Or maybe my memory is at fault ?

mangue: I have to agree. While it might be true that the theoretical value of the best openings is not that bad for Black, the non-losing path is very, very narrow.
Even statistically speaking, White has so many dangerous lines that it is probable that one of them will be found to give him a big advantage. But maybe I am not versed enough in opening theory to speak.

gimli:

AbigailII:

wetware: As for (1), what I read in the Encyclopedia of Chess Variants is that Fred Galvin issued two games in 1958, Refusal Chess and Compromise Chess. Compromise Chess is played with the rules you stated, and Refusal Chess is designed as the over-the-board version, where you have to play one of your two moves over the board, and the opponent can reject it if he wants. It is virtually the same game, but for a reason I don't know in Refusal Chess Galvin decided for the take-the-king version.

Now, I am not saying that one rule is better than the other. I generally prefer take-the-king rules, but in this case it is not a real take-the-king rule, because if it was, the mated opponent could refuse the move which takes the king, so a double check would be needed to win the game (duh!).
Regarding endgames, I don't think that it should not make a big difference (but I share your bias!)

mangue : Where did you read that ? That must be a typo :-)

wetware: I agree that Compromise Chess is a should-be-here variant, but there are at least two possible checkmate rules and II am not sure which one is better. Although your ruleset makes perfect sense, the take-the-king variant also does, that is, if you have only one way to get out of check, you have lost the game. When you are not in check and have only one legal move, it should probably be counted as stalemate.

Move-and-a-half chess is an interesting idea, that I didn't hear about before. Probably only play-testing can tell whether games will not always be n times a single move, followed by a big series which leads to checkmate.

mangue : Yes, I would love to see multi-move variants here. They are well suited for turn-based play because the games are usually short. Marseillais is good, but my personal preference goes to Double-Move Chess (the take-the-king equivalent).

AbigailII: You have a point here. It would be preferrable to have marked promoted pieces, although without it the game would still be more playable than say, Cloning Backgammon without marked "race" checkers :-)

AbigailII, KotDB: OK, Robert Huber told me that they always played with promoted pieces reverting to pawns once they were taken. I hope that we will agree on this rule.
It avoids the "queen factory" trick, but sets a little problem : in order for the interface to be completely "Brainking-compliant", all info should be displayed on the board, so that the promoted pieces should be somehow marked. Although it is almost always quite easy to remember what pieces were promoted.

AbigailII, KotDB: Yes, that should be made clear and now that you rightly pointed that out, I realize that I am not sure about the author's intention in that case. I will ask him by e-mail.

mangue: You mean "even if I didn't manage to draw" .
Yes, I had a huge material advantage in this endgame, but it was probably still a draw.

emmett: I don't think that we need to be so restrictive, as your proposal would make pawns in hand completely uninteresting. If pawn drops are limited to ranks 2 to 6, they are already of controlled danger, but even that restriction does not seem necessary to me. Don't forget that when you capture one of your own pawns, you are generally "wasting" a move and weakening your position, in compensation for the new pawn you get in hand.

One could discuss forever about how everyone would like the rules to be. But I don't see why Fencer should implement anything else than either the original rules (which he did), either the actual rules as corrected by the inventor (which have been thoroughly playtested by german players).

AbigailII: Yes it is easier to get pawns in hands, as far as you are not concerned with making holes in your position, that your opponent can take advantage of. I have experimented with the Rxa7xb7xc7 opening (yes that is a bit naive) and that was a disaster. In the opening and middlegame, I don't think one gets more pawns in hand than in Loop Chess.
Now when we talk about the endgame, you are right that it is easier to get pawns in hand. But this is a tactical element which can be taken into account by the players. It makes pawns more valuable pieces that they are in normal chess. You may like it or not, but it is not a fundamental flaw, like the impossibility to win "won" games would be.

AbigailII: In that case it would probably be enough to bar pawn drops to the seventh rank (drops to the sixth are much less dangerous), like it is done in some local variants of Bughouse Chess.
But consider that in Loop Chess pawns can be dropped on the seventh and then promoted, and that nobody seems to complain about it.

Although the rules used here are a copy/paste of the version originally posted by the inventor Robert Huber on the chessvariants.com website, I think that Recycle Chess should be played with normal promotion, for the two following reasons :

- Robert Huber has changed his mind inbetween, and all games I have played with him, plus all (numerous) games he played in the circle of german bughouse players were played with normal promotions. Me and him have even designed a (flawed) endgame study which was based on promotion. The only goal of the original rule was to use a single box of pieces, which is of course irrelevant when playing online.

- When the game is played without promotion, it becomes very hard to win endgames, because the pawns become quite useless. For instance, the defender king can head for the 7th and 8th ranks where no pawn drop can molest him any more. This is likely to become a real problem when the general skill level will increase, because in this game it is much harder to win by a direct mating attack than in Loop Chess, both because traded pieces disappear forever and because the king can escape by taking his own pieces.

When I asked Fencer if he could reestablish the promotion rule, he told me that he did not want to make the change for the moment and that the matter should be discussed here first, because :

- He doesn't like to make rules change after the game was published.

- He played some live Recycle Chess with Bobes, who said that promotions were problematic, because they allowed a player to multiply queens too quickly by playing the queen on the eight rank, dropping a pawn on the seventh, capturing the queen with the pawn, dropping another pawn on the seventh, and so on. While this observation certainly makes sense, I don't think that it overweighs the draw danger. And if a player has enough time to set up such a repetitive manoeuvre, he can probably win in other ways too.

So, Recycle Chess players, what do you think about it ?

AbigailII: It is not, in the same way that you cannot capture adverse pieces while castling. Similarly, after 1.Nf3 you can't play 2.f2xf3, but you can play 2.g2xf3.

Wooohooooooooo ! Thank you Fencer, this variant rules !
Talking about rules, here are them in short :

A player can capture a piece of his own (except the king), which then becomes part of his stock. When a player has got a piece (or more) in his stock, he can - exactly like in Loop Chess - anytime, in place of a normal move, drop it on any empty square, except the first and last ranks for pawns. One can deliver check or mate in this way.

A king can escape a check by capturing one piece of this own. Unlike Loop Chess, all pieces captured to the opponent are removed from play forever. One cannot capture an own pawn en passant !

dameningen: You are right, it is probably better if the same player made one move for White and one move for Black before the others picked the side.

Instead of making tries or educated guesses in order to make the game more balanced, why not using the "pie rule" ? It has the great advantage of getting rid of the burden of finding the fair opening conditions and passing this burden to the players.
Here is how it works (in the case of a game with an advantage to Black) : Player A (White) plays his first move, Player B (Black) plays his first move, and then Player A has the right to choose between playing on normally or reversing the colours. In the latter case, Player B takes White, starting from the same position.
The effect is that Black has to find the first move that doesn't give too much of an advantage to either player. The slightly annoying side effect is that White will try to find a first move after which all responses lead to an unbalanced position.

grenv: OK, I didn't know. No problem with me, I like it with en passant too. But with visible pawns, of course !

grenv: Actually I checked the original rules on http://www.chessvariants.org/incinf.dir/darkness.html and it says that en passant is not allowed in Dark Chess. So what we have here may even qualify as a bug.

King Reza: Thank you for the fast answer ! But I still think that it is a wrong implementation. It is the only case when you can't see the whole set of your legal moves by looking at your board, and it requires to do a lot of unnecessary clicks in order to gather an information which should be pushed to the player automatically.

Is en passant allowed at Dark Chess ?
If not, all is perfectly fine.
If yes, one should see the pawn which one can take en passant. Otherwise, there would be no other way to know that an en passant is possible without trying all potentials en passant. And discovering it to be possible would give the same info as seeing the takeable pawn.
In both cases, the rules should say a little something about it.

Chicago Bulls: OK I understand, I suppose that this has be done for chess openings database, but I had never seen it before. Now, it seems clear that it requires a great number of high-level games, and I don't think that we have either of these in Ambiguous Chess yet.

Chicago Bulls: Thank you for this work !
What is backsolving ? How would it tell which moves are better ?

Chicago Bulls: That is very nice, good job ! But the numbers make me suspect that you counted unfinished games as draws, because at the moment I write this message the counters show only 726 finished games.

Chicago Bulls: I fully agree that my first suggested option would make the game less interesting because defence would superseed attack.

Chicago Bulls: In your example, grenv would probably like 8.exd5 to be rejected by the system as illegal.

grenv: If my question wasn't, your answer was very clear :-)
Making moves that leave the king in check illegal is indeed an alternative formulation in my personal ruleset ( http://www.pion.ch/echecs/variante.php?jeu=ambigus&rubrique=regles&changer_langue=E ) . Basically it doesn't change the game at all (except for the stalemate, but I like the fact that stalemate is a win), has the advantage to cut off silly mistakes, to make the game more chess-like, but the disadvantages to make the rules more difficult to understand, three times as long and more difficult to implement.
The last reason is enough to make any programer prefer the simple no-check no-mate formulation, and even if I supported your proposition, I am sure that Fencer would not. He didn't implement checks in either Atomic Chess or Extinction Chess, and rightly so imho.

grenv: That is something that could be said about Atomic Chess by someone playing his first game, giving an orthodox check, and seeing his opponent answering by ignoring the check and blowing his king up !
Did you mean that one should disallow to choose a move leaving the opponent in check, or only redefine "checks" so as to avoid that a player can lose his king in one move (that is, making those moves illegal instead of losing) ?

Harassed: Actually it was a nice "king capture in 4", which is analogous to a mate in 3. However, I didn't see it coming at all, probably disregarding the possibility that White would not choose the capture on d5 to be made by the black queen.

WhisperzQ: This is 99.9% correct. The only difference is that Fencer did it (rightly) so that when more than one piece can take the king, selecting the king's square as destination wins the game outright, the opponent does not have to choose who will eat his king.

plaintiger: Questions about rules do not bug me ! Although you already got the answer, I would add that in any chess variant saying "no check or checkmate, the goal is to take the king", it must be understood as "you are allowed to leave your king open to capture, though you will lose the game if you do so".
Actually, you can still talk about "check" (threat to capture the king in the next move) and "checkmate" (unstoppable "check"), but taking these concepts out of the game rules make them much simpler to state.