Chessmaster1000: AbigailII: there's at least one game with a position that repeats itself.

Can you explain in more details this.........

Eh, you have a game, and the positions (that is, where the pieces are on the board, and whose move it is, and if you have a cube, the value of the cube) after move N and M (for N and M not equal to each other) are the same. If that can happen in a game, you have an infinite amount of different backgammon games (if the position after move N can occur after move M again, it can also occur after move 2M - N, 3M - 2N, 4M - 3N, ..., kM - (k-1)N, k >= 0).

If positions cannot be repeated, the number of different games is finite - as the number of different positions is finite.

Chessmaster1000: The number of different backgammon games is finite if, and only if, there's at least one game with a position that repeats itself. And that's not hard to construct - just take a game with both sides having 14 pieces on their 1 spot, and the remaining pieces not having broken contact. Then repeatedly, knock of the single piece. Eventually, the position must repeat itself.

playBunny: For the last time. But you don't seem to be able to grasp the concept that rules should be complete, and not refering to things that aren't defined.

• The rules of backgammon (as stated on THIS site, not rules of backgammon defined by some other identity) nowhere state that if it is possible to move with both die, you have to do so. (This is your MDU rule).
  
• Therefore, the "no swapping possible if there's no legal move for the second die" isn't referring to the MDU rule, because there is NO MDU rule.
  
• Considering that you have to pass if there is no legal move available (no my words - read the rules), and you call this situation "impossible moves", it seems that what you call "impossible moves" is what the rules call "no legal moves".
  
• Again, the rules do not define any MDU rule.
  

Now, either quote the specific part of the rules that define your MDU rule, or stop using arguments that there is an MDU rule.

playBunny: Considering the rules don't define the MDU, nor does the game enforce it, I doubt that The player could not make a legal move with the second die refers to the MDU.

Note that the rule above mentions legal moves as well: If the player cannot make a legal move, he is notified about this situation by a message "You cannot make a move" and must pass this move to his/her opponent by performing an "empty" move - clicks on one of sending buttons. Such move is displayed as "pass" in the game notation.

playBunny: Given that it's an example of the MDU rule, isn't you saying "(or at least, according to the rules, you shouldn't be able to swap the dice)" an agreement that these moves are against the rules?

No. It's just that I can't remember ever encountering the situation I described, so I don't know for sure whether the swap dice link will work or not. All I'm saying is that the rules claim the swap dice link will not work in that situation. But the proof of the pudding is the eating.

Er, that's an example of the kind of illegal move that we are already been discussing, ie. those which go against the maximise-dice-usage rule.

Whatever. Then you tell me what's meant with the illegal moves in the rule that states the swap dice link won't work. If you're going to dismiss anything as being in another class, you tell us what it means. You seem to have a good idea...

playBunny: Can you describe a class of illegal moves that is different to what we're discussing?

You have two stones left, on your 4 and on your 7. Opponent has 2 stones on your 3. You roll 3-4. You can't swap the dice (or at least, according to the rules, you shouldn't be able to swap the dice) because you are not allowed to move with the 4 first.

Walter Montego: You can say what you want AbigailII, but I find the rules misleading on this point or at least not as straight forward that I would know just from a casual perusal of said rules. Perhaps you could write a clearer version and send it to Fencer?

So, while I think the rules are clear, and you think they aren't, you want me to write clearer rules? That's absurd. If you find the rules to be unclear, you write clearer rules. I don't have a problem with the current set of rules.

Chessmaster1000: Imagine a Chess bug that allows Castle when King is threatened.

Would that be a "bug" where the rules say you cannot move a king through chess, or with rules that allow it?

Currently, in Backgammon, the game acts according to the rules. (With the rules the ones found on this site).

Hrqls: Are you trying to make a point? If so, what is it? I think we're all aware of the reasons why dice can be swapped. My point is that the rules say that if moving first with the second die is illegal, the game prevents you from swapping the dice. Ergo, if you can swap the dice, moving with the second die first isn't illegal. Note that if you roll 4 + 3, and you cannot move the 3, for instance you're on the bar and the 3-point is occupied, you cannot swap the dice.

playBunny: It would be different if the web page were to explicitly state that either or both dice may be used

Well, it does. At the bottom of the rules pages, under the heading Other important rules:

• If a player wants to use the second die first, he/she must click on "Swap dice" link below the game board. There are several situations when the link is not shown:
  • Both dice show the same value.
  • The player could not make a legal move with the second die.

And further up the page, when discussing movement of the pieces: If two different numbers are rolled, the player can make two moves at this turn. He/she takes the first (left-most) die value and moves one piece the same number of spaces. Then he/she does the same for the second die.

To me, there's no question about it. Moving off any die first, even if that blocks movement off the second die is allowed. If it were illegal, you wouldn't be able to swap the dice.

As Wil says, if he were playing on a physical board he would do the right thing.

I've never played backgammon on a physical board. Of all the games that you can play here, I've only played a few on a physical board, and backgammon isn't one of them. (Chess, Anti-Chess, Checkers, Halma, Line4, Reversi, Battleboats, Battleboats Plus, that's about it).

playBunny: I use the following logic: if I do a move that is allowed by the rules, it's not an illegal move. The rules allow you to use the die in any order, without restrictions. That's good enough for me. Sure, it's different from the rules from the international backgammon federation, but there's no doubling cube here either.

playBunny: It's against the rules

It's not against the rules as presented on the rules page.

playBunny: Aye, the IP address can be used to help in these matters.

No, it can't. An IP address is not a good indicator for personality. There are large ISPs out there with millions of customers (like AOL) that funnel most of the outgoing HTTP traffic through a relatively low number of proxies. And since it's the proxy that makes the connection to Brainking, it's the proxy's IP address that shows up. And if it's not web proxies, it can be NAT boxes. Ever used a laptop with a wireless connection? Chances are, you're behind a NAT box which means that anyone on the same wireless network will show up with the same IP for the outside world.

WhiteTower: because EACH GAME counts, towards statistics and final ratings.

No. Non-rated, non-tournament games don't count toward ratings or standings. And often, tournament games don't really matter for standings either - if for instance in a 6 player section, one player already has 5 out of 5, and you have 2 out of 4, it doesn't matter whether you end up with 2, 2.5 or 3 points - you're not making it to the next round anyway. Furthermore, in a N-wins match, draws don't count at all.

Finally, there's a tactical element. Suppose you're in a 6 player section. Your current score is 4 out of 4, your opponent has 4 out of 4 as well. There's one other section, and it's already know there's a single winner there. Suppose you, your opponent, and the winner of the other section are all equal in stength, so you estimate a 50% chance of winning any game between any two of you. If you play for a win, you have a 25% chance of winning the tournament - 50% chance of beating the current opponent, and 50% chance of beating the other winner. But if you go for a draw, your chance of winning the tournament increases to 50%! (25% of being a solo winner, 25% of joined winner). I guess offering a draw is the closest you can get to making a cube decision on BK. ;-)

WhiteTower: Who says a win is only a few moves away? Besides, against some players, a few moves takes a few weeks anyway. I don't understand your shouting of VALID. If there is a draw, then the players of their draw had, for them, valid reasons to make it a draw. Don't assume that if you wouldn't agree on a draw in certain situations that noone else would.

WhiteTower: To finish a tournament round? Because you're about to start a three week vacation? Because your opponent offers a draw and you're behind in pipcount? Just because you can? Because a draw finishes the game, freeing a game slot, so you can participate in the next tournament?

alanback: think I have noticed that a 3-wins match counts the same as a single game win -- is that correct? Seems like it should count for more.

Why should it count for more? Is a 2-1 win, with 15 draws a bigger win than a 1-0 win with no draws?

Hrqls: as those matches are calculated as a draw i would expect 2 games with the same player, directly after another, win and loss, have the same result as the 2 game match which was a draw

No, that's not what I expect. There is a difference between two one-game matches, and a single two game match, and that's the fact that in with the two matches, there's a rating adjustment after the first match, and unless there was no rating adjustment, the ratings of the opponents at the start of the second match differ from the ratings of the opponents at the start of the first.

Compare it to interest on a bank account. Say you have an account that gives 10% of interest a year, you have $1000 on that account - and you keep the money in the account for two years. How much interest have you made in those two years? $200? (10%/year of $1000 for 2 years) Or $210? (10% of $1000 for the first year, 10% of $1100 for the second year). Or even $215.50 (interest added every 6 months)?

grenv: Yes, it's a flaw. I was describing the situation how it should be.

Hrqls: shouldnt a win + a loss equal out to a draw

No. A win followed by a loss is slightly worse than two draws, while a loss followed by a win is slightly better. It's easiest to see when you have two players with equal rating, and an equal number of games played. Assume their current ratings to be R. Then a win will give an increase of r points, a loss will give a decrease of r points, will a draw doesn't change the ratings. So, after drawing the first game, it's still r points change for a win/loss, and no difference with a draw. With two draws, both players still have rating R. But what if player A wins the first game? Then her rating will be R + r, while player B's rating will be R - r. So, the expected change in rating for player A for the second game will be an increase of p for a win, a decrease of s for a loss, and a decrease of q for a draw, with 0 < q, p < r < s. So, if player A wins, then loses, his rating will be R + r - s < R. And player B, who first loses, then wins, will end up with a rating higher than R.

A win and a loss will be equivalent to two draws only if the rating is calculated after the entire match - but not if you calculate ratings after each result (which is what happens on Brainking).

playBunny: In chess I believe you play only single games and each game is worth 1 or 1/2 a point whereas in backgammon there are matches worth multiple points.

It's not as simple as that. The chess rating system works just fine over longer matches - in fact, it works even better. If the real rating of two players would be known, one could calculate by which margin a player would win (or lose). For instance, a rating may predict that one player would win 65% of the games. Obviously, this would never be possible in a single game (the score being one of 0%, 50% or 100%), but in a 10 game match, it certainly is possible to get 65%, or at least get closer to it than 50%. In chess, if players play a match of more than one game, or even a complete tournament, ratings aren't adjusted game-by-game, but the result of the entire match or tournament is used. So, if you play a match or tournament, and according to your rating, you should score 58%, but you only scored 45%, your rating will drop.

Hrqls: By default, in a money game, you only get double/triple points for a gammon/backgammon if the cube is on 2 or more. This is called the Jacoby rule.

I also downloaded gnubg, and I don't think it's playing very good. I played a money game for a while, and it didn't take me very long to get a 132-16 lead. And I'm not a good backgammon player at all.

Hrqls: Read the articles at http://www.bkgm.com/rgb/rgb.cgi?menu+matchplay

Hrqls: That's the Crawford rule, which states that if one player is 1 point away from winning, you can't use the doubling cube during the first game where the player is 1 point away from winning. But one can use the cube on any subsequent games.

Luke Skywalker: A better system would be based on 12

You mean, a system with 12 inches in a foot, and 12 * 440 foot in a mile? Or with 12 pence in a shilling? Or 12 troy ounces in a troy pound? Or 12 (US) gallon in a winekeg? Or 12 points in a pica?

I prefer the metric system not because 10 is preferable over 12 (probably not), but because it's consistent. It's based on 10, and only 10. And it has just one system of weights, and just one system of volumes.

Now, back to discussing backgammon.

martinbr: During a backgammon match, a score is indicated for each player.

If you are referring to the Points followed by the players name, it's the number of pips required to bear off all the remaining stones.

Walter Montego: You keep saying "it's not auto-pass -- it stays your turn". Does that mean your clock doesn't stop, until you've opened up your home board -- because "it is still your turn"?

I rather have an auto-pass (or whatever you'd like to define it) in the beginning. That is, if I have lost the roll, I don't see the point in having to have to push the 'pass' button. I find it annoying enough to be tempted to write a bot that makes the passes for me.

grenv: All the current backgammon tournament games are 1 point matches.

Backgammonfan28: That site has problems with its random generator - but it doesn't show in die rolls. It pregenerates the die rolls for an entire day - a roll for every millisecond. And it's the millisecond in which your HTTP request arrives that determines your roll. Not a problem for backgammon like games - but it's a serious problem for Jamble tournaments. Which they still haven't fixed, and is one of the reasons I let my membership there expire, and got a membership here.

Hrqls: Strange. The rules of Ludo as described are quite different from "Mens erger je niet", as I have played on both side of the Atlantic. (Doubles? Penalty on three 6's? Another throw when taking an opponents pawn? Play dice in the order you want? None of this is in the rules of "Mens erger je niet")