I'm glad to find a forum about chess variants. Please visit my page about chess variants. It contains both interesting historical variants and my own suggestions of "improvements" of chess (at least they are good for training purposes).
http://hem.passagen.se/melki9/chessvar.htm

Pedro Martínez: I agree with that. The implementation does seem backwards in this regard.

Seems like the ice age event happens simultaneously with the move... which is fine, but the rules should point that out.

joshi tm: Well, I would personally like Fencer to change the implementation of the game instead. In my opinion, checkmate should take precedence over the effects of an Ice Age. The Black delivered the checkmate with the 20th move, while the Ice Age occurred after the 20th move of the Black (as defined in the rules).

pedestrian: Whoa, overlooked that. What a crazy game, finally the mystery is solved.

Fencer can you add that to the rules section please?

joshi tm: The funny thing in Pedro's example is that White won because Black lost his king (it was isolated as a result of the ice age). That seems to indicate that the Ice Age happens before mate is registered.

That one does not count. It's again a direct hit checkmate, so there's no chance for the Ice Age to prevent mate anyway.

Thom27: ok well done anyway!

Justaminute: ooops! Indeed I made the game private, I didn't think about this. Is there a way to show the game anyway? If not, you have to trust me or try yourself...

(OTOH this is good luck: no one will see how I have bungled the presumably mating move #20)

Thom27: good, but the game seems to be private.

I have tested how it is implemented: Ice Age takes precedence over mate: game

(See also before move 20 of black )

wetware: The *test* for mate is after the 40th move.... but the *definition* of mate relies on knowledge of what the king *could* do next move.... therefore checkmating takes precedence in this case - it happens one move before the other event.

grenv: I'd still like to hear your answer to this question: to which position do you apply the test for mate?  Is it (my contention) to the position at the end of move 40--before the ice age?  Or is it to the position after the ice age adjustments--with White about to make move 41?  It's a clear question, I think...and crucial.

If you claim that the ice age adjustments between moves 40 and 41 must be taken into account, note those same ice age adjustments could iinclude a black king's being frozen to death at the same time that white's king is mated.  Or you'd be stuck claiming that you only consider the ice age consequences for some purposes that you choose, while ignoring other consequences of that identical event.

grenv: Oh, and one last comment... whether you know it or not, you are taking the possible next move into account when assessing if it's a checkmate.... otherwise it makes no sense. If you don't see that then it's no wonder you don't see my larger point.

You might google parallel lines in non-Euclidian geometry if you want some ideas on how interpretation of definitions should not be swayed by your experience and pre-conceived notions.

wetware:

from thefreedictionary.com - but all definitions are essentially the same

check·mate (chkmt)
tr.v. check·mat·ed, check·mat·ing, check·mates
1. To attack (a chess opponent's king) in such a manner that no escape or defense is possible, thus ending the game.

After move 40 an escape *is* possible if the ice age event would cause the king to avoid capture.

Honestly, you people think this is opinion - it isn't... we are trying to interpret the rules as written. I believe my interpretation is the only possible interpretation.

*Opinion* might be that this rule isn't a good rule and should be rewritten.

grenv:
"point 1... Move 40 is defined as being different in the rules... assuming that it should behave the same is plainly wrong."

Plainly (please read for yourself), there is no such definition of moves 20, 40, etc., being inherently "different".  But by rule something special does happen after each of those moves (assuming, of course, that the game does not actually end on any of those moves.)  I do hope you agree that a game can be ended by a black move 20, 40, etc.

"point 2... Actually my sequence is the same as yours, I just have a different definition of checkmate... my definition is;
"if the white king is in check and cannot legally move out of check on his next move, then he is checkmated." "

Checkmate ends a game.  There is no "next move".  Plainly, the mating move is the last move of a game.  So any definition that demands a reference to a "next move" must be doing so in a hypothetical way, as it refers to something counterfactual--it will not occur.  In my opinion, it's better to avoid that in a definition if that can reasonably be done.

Your definition appears to be:
"if
the white king is in check and could not legally move out of check next
move in an identical situation in a different variant, then he is
checkmated"

Plainly not.  My test for mate after Black's move 40 would be the same as the test applied after moves 21 through 39.  I think that would be the same evaluation applied in conventional chess.

And please tell me when you perform the test for mate: before the ice age?

pedestrian:
I agree playing a game would be the simplest way to clarify things. There is no right answer, only opinion. I expect it would take a long time to get a change made anyway. I doubt it is a high priority, particularly as Kleinme can't find a single case where this happened in practice. I can't start a new game at the moment but I'm hoping someone else willl.

grenv: There are three separate issues here. 

wetware:
point 1... Move 40 is defined as being different in the rules... assuming that it should behave the same is plainly wrong.

point 2... Actually my sequence is the same as yours, I just have a different definition of checkmate... my definition is;
"if the white king is in check and cannot legally move out of check on his next move, then he is checkmated."

Your definition appears to be:
"if the white king is in check and could not legally move out of check next move in an identical situation in a different variant, then he is checkmated"

I like my definition better.

grenv: I think that the crux of our disagreement is this: when does a test for mate occur?  I contend that a move that would--in a given position--suffice to produce mate on any move numbered 21 through 39, would also produce mate on move 40.

I think the move 40 sequence is: (1) black plays a move, (2) one tests for mate, (3) if not mate, an ice age occurs, (4) one tests for frozen king(s).
I think your move 40 sequence is: (1) black plays a move, (2) an ice age occurs, (3) one tests for mate or frozen kings.

In your sequence only, it has become simultaneously possible for the white king to be mated and for the black king to be frozen--yet another situation not mentioned in the game description at chessvariants.org

nabla: In conventional chess, can I be checked (or even mated) by a pinned piece?  Or is that another optical illusion?

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).

Justaminute / Nabla: I believe that in Atomic chess you should be considered to be in check if a move of your opponents could blow up the king.... i think that is a mistake in the implementation... however it doesn't really matter or change the game too much.

In this case you're asking the wrong question. Checkmate occurs at the end of move 40 - However - the definition of checkmate is that the king cannot move out of check on his next move. Since the next move is move 41, the ice age event intervenes and must be taken into account...

I don't see how the interpretation could possibly be any other way unless it is explicit in the rules (which it isn't).

You can argue that it is a lop-sided game as a result if you like, but I don't think you can argue the interpretation;.

nabla: You only need to alter the rules to the extent of creating the new game, superfluous amendments don’t add anything except the ambiguity that you seek to avoid. You couldn’t pay three check chess without changing the definition of how the game ends. There is no need to do so in loop chess though. The only clarification of the rules that is needed in ice age chess is the assessment of checkmate occurs at the end of move 40 or the start of move 41. There is no need to refine checkmate in this game.

Bwild:

nabla: as soon as your opponent makes his 1st move

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: alternating ice ages would seem to even out the playing field

Justaminute: That would seem to be an argument for how the ice age event goes into effect at all... but once you have the event you should treat it consistently.
Maybe the ice age event should happen every 39 moves instead of every 40 so that it alternates.

grenv:
Which is correct if you assess the position at whites 41st move but not if you assess the position at black's 40th. As black never benefits from being saved by an ice age I don't support the argument that whitr should be able to.

Justaminute: I think the rule is clear and doesn't need clarification.

The ice age event happens between blacks 40th move and white's 41st...

if the event means that white can move out of check (or simply isn't in check any more) then blacks 40th move is not checkmate.

Interpreting it the other way is simply misunderstanding that this is a different game than regular chess... just because the position *would be* checkmate in a regular game doesn't mean it is here.

nabla:
I don't see any reason to rewrite the FIDE rules
If you don't have a legal move the game is over. Nothing to do with taking a king on the next move.
The rules also cover the point about moving your king to a square where it is under attack. Again the question is , is it defined as being under attack on bliack's 40th or whites 41st? I vote black's 40th

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" ?

nabla:
I'm not sure your definition of checkmate is correct. Fide's website says:

The objective of each player is to place the opponent’s king ‘under attack’ in such a way that the opponent has no legal move. The player who achieves this goal is said to have ‘checkmated’ the opponent’s king and to have won the game. Leaving one’s own king under attack, exposing one’s own king to attack and also ’capturing’ the opponent’s king are not allowed. The opponent whose king has been checkmated has lost the game.

The question in ice age chess would be does the definition of legal move apply at the time of black's 40th or white's 41st? Clearly not an issue in standard chess as the board is the same. I would vote for on black's 40th for symmetry.

Don't forget that forcing a capture of the king is not the idea... otherwise stalemate would be a win. We still need the king to be in check for a checkmate to be valid.

DarwinKoala: At first I thought that enforcing the Ice Age before evaluating the position would be too big an advantage for White because he can mate on move 20, 40, 60 in a conventional way but Black cannot. But maybe this evens out a bit that Black has a serious advantage in always having the last move before the Ice Age.

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.

pedestrian: True,
happy to play it but I can't make or accept invites until I get below 50 games.

Justaminute: It shouldn't be too difficult to construct a game where black gives mate from a distance on move 20.

wetware:
I agree ice age should be after black's 40th move. If that is not the case there is an inconsistency between being black and white as it is definately after the white 40th move. Playing an unrated game following the moves of the game in question and varying at the 40th move would determine what actually happens on bk.

kleineme: I'd be much more inclined to ask the game's inventor (or leading players, if the inventor is not available), rather than basing anything on the actual implementation here at BK.  There are things here that could stand improvement.

I'm a variant lover but not an ice age player, so feel free to discount my opinion.  But I'd much rather see the rules of what constitutes "mate" remaining consistent throughout the game, no matter what the current move number happens to be.  Let a move be completed before an ice age occurs.

The "taking the king" argument leads one astray.  If you follow that "logic", a king could move into some checks, secure in the knowledge that an ice age was about to save him.  I'm sure we don't want that.

In my mind, ice age precedence is logical, given that "mate" is a shortcut to taking the king. If, at the end of move 20n an Ice Age occurs and means that white can no longer take the king, then the game would continue.

Bwild: If White had played 40. Bd4 instead of 40. Bb4, then 40.- Re1 would have been mate unless Ice Age takes precedence. But even if it's not mate then it would have been a possbile move because the rook wouldn't freeze with the white Knight on f2 as a neighbor.

in RGroszkiewicz example....there was no check mate with the rook being moved to E1

I agree with lukulus that it would be more logical when the mate would be checked (and counted) first before the Ice Age occurs, although his example isn't a proof that it's actually handled this way. As far as I can see there is no such proof in the database. I looked at all games which end with a mate after Black's 20th (40th, 60th, ...) move, but all games I've found are by direct contact with the white King or by a Knight's move (see link list below). This is not a positive proof that Ice Age occurs first, because maybe no one yet dared to try to test the behaviour ;) The other positive proof would be a game that continues after a would-be-mate after Black's 40th move, but that is hard to find in the database because in such a game the move wouldn't even be marked as a check, so one would have to go through all games with at least 41, 61, etc. moves. So we should simply wait for the one with the inside knowledge: one short post by Fencer would be enough: "Mate" or "Ice Age"? :-)

20th move
Ronin - talen314
El Cid - Pioneer54
Nuno Reis - pauloaguia

40th move
Franklin - volor
yoyudax - asdf
Jaymom - chudu1980

60th move
diogenysos - basplund
Brainwave - Jatack

P.S.: Well, after looking at all those games once more, in each of them actually an Ice Age occured although it's already mate. Maybe that's an indication that Ice Age occurs first?

That mate occurred in White's 40th move. The Ice Age occurs after Black's 40th move.

I think Ice age will come after check ar mate. Its logical, Mate is end of game.
Ledové šachy (Pioneer54 vs. lukulus)

RGroszkiewicz: it would appear that white keeps playing

RGroszkiewicz: If the Ice Age freezes a king, the player who is its owner loses the game. If both kings are frozen at the same time, the game is a draw.