Copenhagen Hnefatafl

Tafl rules
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Adam
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Re: Copenhagen Hnefatafl

Post by Adam » Fri Mar 16, 2012 10:01 am

Hagbard wrote:Image
Edge draw fort based on one edge square only!
Very nice! Though the king is not mobile, so its a draw draw fort. (if the king moves the fort can be destroyed I think)

Hagbard
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Re: About the draw concept

Post by Hagbard » Sun Mar 18, 2012 12:19 pm

MaC wrote:In my opinion there are now following good and practicable rules.
1. Black has to surround the king or all his peaces (That's a black win)
2. White has to reach the neutral cities (that's a white win)
3. Every thing else is a draw after 3 time repetition of a field situation
The MaC summary is clear, clean, logical and easy to use and understand also for any beginner.

Image
The situation in the diagram is however very common - quite early in the game white finds all corners inaccessible, and after that has nothing to go for but the draw. The real game has ended already here. If white however can still go for the win (through an edge win fort), there's much more to play for in the continued game, the real fight continues for much longer. Also the constant threat from the very start of the game of this other winning method of white's makes it harder for black to do the quick barricading.

As for repetitions it would be interesting to test if this situation can be induced deliberately.
Last edited by Hagbard on Fri Mar 24, 2017 9:12 am, edited 1 time in total.

crust
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Re: Copenhagen Hnefatafl

Post by crust » Sun Mar 18, 2012 1:48 pm

To summarize (a bit) this very complex issue, with apologies for repeating things:

Copenhagen rules are

Copenhagen Rule #1:
The black (attacker) player wins, if the black pieces surround and enclose all the white pieces, so that the enclosure is complete, with no gaps.

Copenhagen Rule #2:
The white (defender) player wins, if the white pieces create an “edge fort” which fulfils the following three conditions:

a. The king must be on an edge square within the structure
b. The king must be able to move (he must have a free space to move into)
c. The fort must be impregnable to attack

Copenhagen Rule #3:
In cases of repeating moves or perpetual check, where the same board position is obtained three times, the threatening player (not the blocking player) must break off the attack and make an alternative move, or lose the game.


#################################################################

In Fetlar Hnefatafl, it has been found that the white player has a disproportionate ability to force a draw. These new rules do not make draws impossible, but they make them less likely, increasing the chances that the game will end in a win for one player or the other. The Copenhagen rules #1 and #3 limit the ability of the white player to create a draw result, and Copenhagen rule #2 compensates the white player for the loss of this leverage by allowing another way of winning, thus preserving the balance of power between the two players. At least that is the hope!

Now, we have the choice of whether to implement all three rules (strong Copenhagen) or just two rules (weak Copenhagen - rules #1 and #2 only) or just one (super-weak Copenhagen, rule #1 only, which I think is what MaC proposes). I don't mean "weak" in any negative sense by the way, and of course there are other combinations that could exist, like rule #2 only (favours white) or rules #1 and #3 only (favours black).
Hagbard wrote:The situation in the diagram is however very common - quite early in the game white finds all corners inaccessible, and after that has nothing to go for but the draw. The real game has ended already here. If white however can still go for the win (through an edge win fort), there's much more to play for in the continued game, the real fight continues for much longer
I quite agree. Copenhagen rule #2 really livens up the game, by "activating" the edge squares in a new way. It makes the game more "unstable" (not the same as "unbalanced") - in other words, more likely to tip over into outright victory for one player or the other, without actually favouring one player. As for rule#3, I think we still have some testing to do there - will it actually change the way people play, because black faces fewer threats - does it make life too easy for black?
Adam wrote:it is the threat of a perpetual check, not the perpetual check itself, which affects gameplay,
[/quote] Quite right, and rule #3 gets rid of this threat, so we must try and see what the effects of this absence are. Not easy!

Adam
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Re: About the draw concept

Post by Adam » Sun Mar 18, 2012 5:59 pm

Thanks to Mac for highlighting that this thread is getting complex and tricky to follow. And thanks to crust for an excellent summary. This thread is a work in progress discussion that has been developing for some time, so new comers and latecomers will have some homework to do to get up to speed! The draw problem was only discovered when experienced players met in tournaments or in rated games. They are relatively rare, but common enough to stop the game being taken seriously as an international tournament playable game.

Hagbard
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Re: Copenhagen Hnefatafl

Post by Hagbard » Sun Mar 18, 2012 6:10 pm

crust wrote:It makes the game more "unstable" (not the same as "unbalanced") - in other words, more likely to tip over into outright victory for one player or the other, without actually favouring one player.
It's a characteristic of this battle board game already with the Fetlar rules that the fortune of war can rapidly shift. A crucial move behind enemy lines, or shifting the battle from a corner to another etc. The same characteristic has another battle board game - chess; one wrong move and the entire position might collapse. Probably the same thing applies to real battle, so I guess it's a healthy sign for a battle game when the rules work this way.

Adam
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Re: About the draw concept

Post by Adam » Sat Mar 24, 2012 3:57 pm

Hagbard wrote:
MaC wrote:The repetition draw is no problem because it is hard to get and it is possible to avoid.
Maybe it would be instructive with some crust-Adam test games on this, where white in the test (or black) must force a perpetual moves situation to win? Just like the earlier test of the Monstrous forts.
Instructive and fun!

Sorry I've not been playing in the tournament. Computer troubles first and now a new baby girl (third child) to look after have rather confounded me! However crust and I are running some strong copenhagen test games.

Mac is correct that white perpetual check is avoidable with black playing the right preemptive moves. And unavoidable checks and stalemates are what we are primarily trying to remove from the game. However we are also looking at the games balance and win statistics. Clearly black having to devote moves to preventing perpetual check affects game balance. It may turn out that the balance is better when black has to deal with those types of threat. Hence the weak a d strong versions.

crust
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Re: About the draw concept

Post by crust » Sat Mar 24, 2012 7:19 pm

Adam wrote:black having to devote moves to preventing perpetual check affects game balance. It may turn out that the balance is better when black has to deal with those types of threat.
That's true... if black can now leave third-ranks unattended, safe in the knowledge that white can't use the threat of perpetual check against him, that leaves black in a much stronger position, maybe too strong. On the other hand, maybe with enough time and practice, new techniques peculiar to copenhagen hnefatafl will emerge. For instance, I think white may learn to attack the edges much more, exploiting rule #2 to restore the balance?

Experience with hnefatafl has shown repeatedly, that one side has discovered a tactic that really works, and seems for a while unanswerable (thereby unbalancing the game), but after a few more games, a countermove is discovered, and the balance shifts over the other way, (with the words "NEXT LEVEL" flashing across the screen, as it were.) This levelling up has happened several times already, just as it must have happened early in the history of chess or any other game of sufficient complexity.

My own feeling is (and it's just a feeling) that we should keep rule #3 unless it turns out to be seriously bad, because games which end in a perpetual check draw are disappointing anyway, so the threat of perpetual check draw is the threat of inflicting disappointment, which is bad gamesmanship, like saying "you have to make such and such a move, otherwise I will make the whole game really disappointing, and there won't be anything you can do about it!" But we need more testing WITH the rule #3 in place, before we know if the balance is badly affected.
MaC wrote:Maybe it would be instructive with some crust-Adam test games on this, where white in the test (or black) must force a perpetual moves situation to win? Just like the earlier test of the Monstrous forts.
Yeah I'm up for that too. Someone, give Adam and me a research grant :geek:

Hagbard
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Re: About the draw concept

Post by Hagbard » Mon Mar 26, 2012 10:27 pm

Adam wrote:and now a new baby girl (third child) to look after have rather confounded me!
Congratulations on the new little viking, Adam!


Image
As mentioned before, it's easy for white to go for this position from the start in order to force a draw, so this can be abused.

Such abuse can be avoided by expanding the encirclement rule+1 into a rule+4:
rule+2) White win edge fort. White wins if the king has contact with the board edge, is able to move, and it is impossible for black to capture him.
rule+2a) Draw edge fort. If a white fort has contact with the board edge, contains the king, some white piece in the fort is able to move, and it is impossible for black to destroy the fort, white can claim a draw.
rule+4) Encirclement. Otherwise (when the king is not part of one of these two edge fort types) black wins if all white pieces are encircled by edges and by blacks, all linked together with no gaps.

The rule+4 makes the earlier rule+1 obsolete, because rule+1 is a special case of rule+4.
With a rule+4, the position above is a black win. So are these:
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Kratzer
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Re: About the draw concept

Post by Kratzer » Tue Mar 27, 2012 10:34 pm

Congratulations Adam!!! :D

Well made observations, Hagbard! This so called rule+4) sounds very convincing to me.

Does the test version of Copenhagen Tafl (not the tournament one) already include the new rules (at least those 3 established before)? I really would like to start some more Copenhagen matches besides our tournament.

Hagbard
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Re: About the draw concept

Post by Hagbard » Tue Mar 27, 2012 10:58 pm

Roderich wrote:Does the test version of Copenhagen Tafl (not the tournament one) already include the new rules (at least those 3 established before)? I really would like to start some more Copenhagen matches besides our tournament.
Yes, the applet detects the rule+1 encirclement, the white win edge fort and perpetual repetitions.

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