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Topic: Please help me verify the 3-repeat rule (Read 3791 times) |
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chimaera
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Arimaa player #4560
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Please help me verify the 3-repeat rule
« on: Nov 12th, 2009, 8:24pm » |
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Could someone please give this a quick scan and validate my logic here? I'm trying to make sure that I fully understand the "3-move repeat rule" in the Arimaa rules.
I've marked up each board position like so:
// board layout $WhoseTurn-$Pattern #$OccurenceNumber
Code:
2g
+-----------------+ // board layout Gold-A #1
8| d c r h r r c d |
7| r r m h r r r e |
6| . x . x . |
5| . . . . |
4| . . . . |
3| . x . x . |
2| D C D H R H E M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
2s
+-----------------+ // board layout Silver-A #1
8| d c r h r r c d |
7| r r m h r r r e |
6| . x . x . |
5| . . . . |
4| . . . . |
3| . x . x E |
2| D C D H R H M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
3g
+-----------------+ // board layout Gold-B #1
8| d c r h r r c d |
7| r r m h r r r |
6| . x . x e |
5| . . . . |
4| . . . . |
3| . x . x E |
2| D C D H R H M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
3s
+-----------------+ // board layout Silver-B #1
8| d c r h r r c d |
7| r r m h r r r |
6| . x . x e |
5| . . . . |
4| . . . . |
3| . x . x . |
2| D C D H R H E M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
4g
+-----------------+ // board layout Gold-A #2
8| d c r h r r c d |
7| r r m h r r r e |
6| . x . x . |
5| . . . . |
4| . . . . |
3| . x . x . |
2| D C D H R H E M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
4s
+-----------------+ // board layout Silver-A #2
8| d c r h r r c d |
7| r r m h r r r e |
6| . x . x . |
5| . . . . |
4| . . . . |
3| . x . x E |
2| D C D H R H M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
5g
+-----------------+ // board layout Gold-B #2
8| d c r h r r c d |
7| r r m h r r r |
6| . x . x e |
5| . . . . |
4| . . . . |
3| . x . x E |
2| D C D H R H M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
5s
+-----------------+ // board layout Silver-B #2
8| d c r h r r c d |
7| r r m h r r r |
6| . x . x e |
5| . . . . |
4| . . . . |
3| . x . x . |
2| D C D H R H E M |
1| C R R R R R R R |
+-----------------+
a b c d e f g h
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The move eh6n and then a pass would be illegal, correct? It would cause the board layout "Gold-A" to occur a third time. Therefore, if silver makes the move eh6n, then she must make 1+ more moves before she is allowed to end her turn.
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chimaera
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Re: Please help me verify the 3-repeat rule
« Reply #1 on: Nov 12th, 2009, 8:38pm » |
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Also, I should note that I did search and find threads discussing this, but I want to make absolutely sure that I understand this rule. The rule "If after a turn the same board position and side to move would be repeated three times..." is a little ambiguous because it implies a fourth occurrence would be illegal (an initial pattern plus three repeats of the pattern).
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| « Last Edit: Nov 12th, 2009, 8:39pm by chimaera » |
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Fritzlein
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Arimaa player #706
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Re: Please help me verify the 3-repeat rule
« Reply #2 on: Nov 12th, 2009, 8:45pm » |
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on Nov 12th, 2009, 8:24pm, chimaera wrote:| The move eh6n and then a pass would be illegal, correct? It would cause the board layout "Gold-A" to occur a third time. Therefore, if silver makes the move eh6n, then she must make 1+ more moves before she is allowed to end her turn. |
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Correct.
It gets a little tricky to be talking about which steps are forbidden, because the repetition rule deals with which full turns are forbidden.
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chimaera
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Re: Please help me verify the 3-repeat rule
« Reply #3 on: Nov 12th, 2009, 8:53pm » |
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Thank you. I didn't want to clutter up the forum with a repeat ( ) of a topic, but the previous posts I found were just people saying "So if I repeat it X times that's bad?"; "Yes, repeating it X times is bad", etc.
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chimaera
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Re: Please help me verify the 3-repeat rule
« Reply #4 on: Nov 12th, 2009, 8:56pm » |
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on Nov 12th, 2009, 8:45pm, Fritzlein wrote:
It gets a little tricky to be talking about which steps are forbidden, because the repetition rule deals with which full turns are forbidden. |
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And yes, it is very tricky to do this. The approach I've taken in my program is to allow the user to back herself into a corner and thus lose, but not to allow a turn to be ended early if it would be illegal, or to move at the last step of a turn if it would be illegal, or to begin a push on the second-last step if the only way to follow through on the push would be illegal. Implementing this check was very annoying!
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ocmiente
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Re: Please help me verify the 3-repeat rule
« Reply #5 on: Apr 19th, 2010, 1:13pm » |
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I wonder if misunderstanding the 3-repeat rule is very common. I didn't grasp it until game 141408 (http://arimaa.com/arimaa/games/jsShowGame.cgi?gid=141408&s=b), bot_marwin vs. Adanac in the 2010 Arimaa challenge, move 42s. I was wondering why marwin didn't just repeat the position and force Adanac to choose something else.
I read the rule to mean that basically you couldn't make the same move three times, provided your opponent repeated his moves also. It didn't occur to me that the repeated board position doesn't occur 3 times until both players repeat their moves 3 times. I think Adanac put it well in the chat room: Quote:Defending by reversing is cheap so I'm glad the attacker wins the repitition rule.
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The way the works out still seems counterintuitive to me - but I think that the logic of it works out brilliantly.
Of course, I could still be misinterpreting the rule and need some deeper understanding... please correct this if it's wrong.
<EDIT> Should have written "...the repeated board position doesn't occur 3 times until both players repeat their moves 2 times, which would take 4 turns each. The 4th turn of the second player would be illegal.
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| « Last Edit: Apr 19th, 2010, 10:21pm by ocmiente » |
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Eltripas
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Re: Please help me verify the 3-repeat rule
« Reply #6 on: Apr 19th, 2010, 5:15pm » |
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on Apr 19th, 2010, 1:13pm, ocmiente wrote:I wonder if misunderstanding the 3-repeat rule is very common. I didn't grasp it until game 141408 (http://arimaa.com/arimaa/games/jsShowGame.cgi?gid=141408&s=b), bot_marwin vs. Adanac in the 2010 Arimaa challenge, move 42s. I was wondering why marwin didn't just repeat the position and force Adanac to choose something else.
I read the rule to mean that basically you couldn't make the same move three times, provided your opponent repeated his moves also. It didn't occur to me that the repeated board position doesn't occur 3 times until both players repeat their moves 3 times. I think Adanac put it well in the chat room:
The way the works out still seems counterintuitive to me - but I think that the logic of it works out brilliantly.
Of course, I could still be misinterpreting the rule and need some deeper understanding... please correct this if it's wrong.
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You are misinterpreting the rule, the rule is designed in a way that it always helps the development of the game, for example if the game is in a position A and the attacker makes a move so the game is no in position B, the defender moves back to position A, and then the attacker moves again to get the position B, the defender can't return to the position A for a third time so the game makes development.
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ocmiente
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Re: Please help me verify the 3-repeat rule
« Reply #7 on: Apr 19th, 2010, 6:23pm » |
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umm... well... I think what I wrote earlier agrees with what you wrote - so I think you might have meant 'were' misinterpreting, rather than 'are' misinterpreting?
Sorry that my writing was not as clear as it could have been. In short, I think I understand why marwin did what it did - and that its behavior was due to the 3-repeat rule. The 3-repeat rule does not have do to so much with repeating a move three times as it does with repeating a board position (combined with whose move it is), which seems pretty simple on paper - but I expect that many people don't get that the first time they read it... and if they don't, its likely that it won't sink in until they witness a game like the one I watched.
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| « Last Edit: Apr 19th, 2010, 7:29pm by ocmiente » |
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Hippo
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Re: Please help me verify the 3-repeat rule
« Reply #8 on: Apr 20th, 2010, 7:31am » |
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Out of topic ... I have checked no change rule as well ... for example rotating two dogs does not change the board state.
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rbarreira
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Re: Please help me verify the 3-repeat rule
« Reply #9 on: Apr 20th, 2010, 7:37am » |
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The problem is that people keep talking about "repeating" and "returning to" positions (which is actually how the rule is written). The problem is that the first time the position happens, it's not "repeating" itself strictly speaking.
If I understand it correctly, the rule actually means that you can't "have" the same (position/side to move) three times. By using "have" instead of other ambiguous verbs there should be no room left for confusion.
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| « Last Edit: Apr 20th, 2010, 7:38am by rbarreira » |
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lightvector
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Re: Please help me verify the 3-repeat rule
« Reply #10 on: Apr 20th, 2010, 11:20am » |
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I agree. From the game rules:
Quote:
If after a turn the same board position and side to move would be repeated three times, then that move is considered illegal and the player must select a different move.
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I think it would be clearer to say something like:
If after a turn the same board position and side to move would occur for the third time, then that move is illegal and the player must select a different move.
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ocmiente
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Re: Please help me verify the 3-repeat rule
« Reply #11 on: Apr 20th, 2010, 2:23pm » |
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Quote:I think it would be clearer to say something like:
If after a turn the same board position and side to move would occur for the third time, then that move is illegal and the player must select a different move. |
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Yes, I agree with that.
Quote:| Out of topic ... I have checked no change rule as well ... for example rotating two dogs does not change the board state. |
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Hippo, I hadn't even thought about that - but it's an interesting point. Rotating two pieces isn't a legal move, right? Since the board state doesn't actually change?
I went ahead and looked into the threefold repetition rule for Chess: http://en.wikipedia.org/wiki/Threefold_repetition.
From that, it appears that the initial rule did have to do with repeating moves, and not with repeating positions. I think that that is the more natural and intuitive way for people to think about something like this, especially when playing on a board with no computer assistance.
Quote:The first use of such a rule was in a tournament was in London in 1883, but was stated vaguely:
... if a series of moves be repeated three times the opponent can claim a draw.
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It was soon changed to be that the position had to be repeated, along with the side to move, and ability to castle. I think that this is better for the game, but not as intuitive.
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| « Last Edit: Apr 20th, 2010, 3:45pm by ocmiente » |
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Fritzlein
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Re: Please help me verify the 3-repeat rule
« Reply #12 on: Apr 20th, 2010, 2:32pm » |
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on Apr 20th, 2010, 2:23pm, ocmiente wrote:| Rotating two pieces isn't a legal move, right? Since the board state doesn't actually change? |
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Correct. Swapping your dogs doesn't change the position, so it is not a legal move. Also for repeated positions the dogs are interchangeable, not distinct.
Quote:| From that, it appears that the initial rule did have to do with repeating moves, and not with repeating positions. I think that that is the more natural and intuitive way for people to think about something like this, especially when playing on a board with no computer assistance. |
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Yes, for Arimaa too, when there is no computer assistance I would replace the repetition rule with the simpler rule: Your move may not undo your opponent's previous move. That isn't identical to the actual rule, but it is vastly simpler and covers most of the cases. Indeed, bot_bomb uses the "no undo" rule instead of the true repeat rule, and that was good enough to win five Computer Championships.
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Arimabuff
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Re: Please help me verify the 3-repeat rule
« Reply #13 on: Apr 21st, 2010, 2:30am » |
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I wonder how people can even play a fair game without computer assistance especially people who are new to the game. It must be easy to forget a freezing "en passant" or a disappearing piece on the trap because it has been abandoned for one step. The repeat rule is just icing on an already hard to digest cake.
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Fritzlein
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Re: Please help me verify the 3-repeat rule
« Reply #14 on: Apr 21st, 2010, 6:25am » |
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on Apr 21st, 2010, 2:30am, Arimabuff wrote:| I wonder how people can even play a fair game without computer assistance especially people who are new to the game. It must be easy to forget a freezing "en passant" or a disappearing piece on the trap because it has been abandoned for one step. The repeat rule is just icing on an already hard to digest cake. |
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Yes, I expect beginners make illegal moves all the time in Arimaa. On the other hand, that's just how it was for chess when I was learning. I would leave my king in check for several moves, and not know what to do when I discovered it later. I didn't understand when I could or couldn't castle. I thought that pawns could use their opening double-move to capture two squares diagonally as well as advance two squares forward. Admittedly, Arimaa isn't easy to play at first without a rule-checker keeping watch, but it is in good company on that score.
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