Copenhagen Hnefatafl

Tafl rules
crust
Posts: 127
Joined: Sat Mar 21, 2015 9:29 am

Re: Copenhagen Hnefatafl

Post by crust » Sat Feb 04, 2012 4:49 pm

Thanks Hagbard, now I know what the German for "connoisseur" is. There is no English word for it, we use the french one. I am a hnefatafl feinschmecker, and I would definitely note the lack! Copenhagen rules should be enough to punish barbaric behaviour on the hnefatafl board, such as uncouth draw-seeking by white, or relentless strangling by black.

The idea of calling all draws wins for black is not attractive, although it does have an impressive simplicity. I note that it already exists for the case of perpetual check in rachunek tafl.

Adam
Posts: 115
Joined: Fri Mar 20, 2015 1:28 pm

Re: Copenhagen Hnefatafl

Post by Adam » Sat Feb 04, 2012 10:33 pm

Well done gentlemen. Lots of hard thinking going on here. I am up for testing the copenhagen interpretation, where the king can appear to both win and draw simultaneously. It sounds like a lot of fun. Before we know it we'll have sappers quantum tunneling through the draw fort walls. (berserk does this already of course!) My concern is that white is in fact getting yet another form of leverage over black. I find the bunker particularly easy to form in games, its the easiest to prepare for while pretending to do something else, and is quite hard to prevent unless you keep the board edge busy as black. So that is the additional pressure placed on black right from the start. But then if all white draws are given to black as wins, the game is thrown out of balance the other way it seems. Not that I would advocate that course personally. Edge forts seem to be a good way forward. They make sense as they bring to mind forging a connection to the outside world of reinforcements and supplies which can perpetuate a siege. I'm not convinced that two men pinned to the board edge with the king stuck in the middle in a centre for counts as an edge fort. I would say an edge fort has to have the king as a part of it, otherwise your king is surrounded. One could argue though that if you can build an edge fort with regular soldiers, and have your king on the board edge elsewhere, that this would count as kings edge fort. But its stretching the point rather.

So a kings edge fort where the king is able to move within the fort counts as a white win?

We'll try it. I feel that it should just be a draw as white does not need more leverage but less. But lets give it a go as it sounds so interesting.

I would like to suggest testing it with forbidden perpetual check. Certainly if white can win with an edge fort. But rather than saying that white loses in a perpetual check situation, we simply say white HAS to play a different move after 3 repeats. That rule definitely makes blacks job easier, which is why I would then happily go along with the mobile-king edge fort win. Sounds like a cracking good game.

Hagbard
Posts: 406
Joined: Sat Mar 14, 2015 6:07 pm

Re: Copenhagen Hnefatafl

Post by Hagbard » Sun Feb 05, 2012 1:24 pm

Adam wrote:I am up for testing the copenhagen interpretation, where the king can appear to both win and draw simultaneously. It sounds like a lot of fun. Before we know it we'll have sappers quantum tunneling through the draw fort walls.
We have Hnefatafl players very well informed in quantum physics here!
Adam wrote:My concern is that white is in fact getting yet another form of leverage over black. I find the bunker particularly easy to form in games, its the easiest to prepare for while pretending to do something else, and is quite hard to prevent unless you keep the board edge busy as black.
I'm in the end game of an instructive Copenhagen test game with crust right now. It turned out that the opening and middle game remained pure Fetlar, unaffected by the two rule additions, except that now the center draw-fort option is off. There did not seem to be space for a fort at the edges until the end game where black has only 16 pieces left, 12 of which are blocking the corners and 4 left to fight white. White is left with king and 5 men. Even then it doesn't appear to be easy to create this fort, and even more difficult when the king should end up inside and moving. Although I think that a stronger player would manage to do it.
Adam wrote:Edge forts seem to be a good way forward. They make sense as they bring to mind forging a connection to the outside world of reinforcements and supplies which can perpetuate a siege.
White pieces on the board edge bring to my mind that they do connect to the surrounding terrain of the board. And so can be imagined to enter that terrain, circumvent and re-enter the board from another direction, killing blacks and breaking the barrier from outside, and so the game is not definitely over yet but a draw. I guess this is actually also the idea behind the edge fort win; the king is connected to the surrounding terrain, running and cannot be captured, so he escaped.


The games archive contains in all 383 Fetlar Hnefatafl 11x11 games since 2010.12.23, of which only 29 are draws. Some of the "draw games" are test games or abandoned games because of applet deadlock or some other reason and are ignored.

Left are 15 draw games. With the suggested Copenhagen rules, 8 would remain draws and the rest turn into 1 white win and 6 black wins. This seems to be but a small change and a modest price for voiding all early draws.

It's interesting that these draw games give examples of about all draw types.

crust / Hagbard. Fetlar Hnefatafl 11x11, 91 moves, 2012-01-23 19:07:05 (correspondence) draw
Hagbard / Angle. Fetlar Hnefatafl 11x11, 79 moves, 2012-01-11 12:31:18 (live play) draw
chuck ward / Hagbard. Fetlar Hnefatafl 11x11, 27 moves, 2012-01-05 22:25:04 (correspondence) draw
Center fort. Would be encircled and turned into a black win.

Adam / crust. Fetlar Hnefatafl 11x11, 100 moves, 2011-08-31 23:09:46 (live play) draw
Fine example of a garbo fort. Would still be a draw.

Roderich (tourn.) / crust (tourn.). Fetlar Hnefatafl 11x11, 132 moves, 2011-08-15 20:31:09 (live play) draw
Draw by agreement. Would still be a draw.

Adam (tourn.) / Roderich (tourn.). Fetlar Hnefatafl 11x11, 36 moves, 2011-08-14 21:39:16 (live play) draw
Perpetual check. Would still be a draw.

Hagbard (tourn.) / Roderich (tourn.). Fetlar Hnefatafl 11x11, 50 moves, 2011-08-12 17:53:15 (live play) draw
Center fort. Would be encircled and turned into a black win.

Repoupoune / Roderich. Fetlar Hnefatafl 11x11, 43 moves, 2011-08-11 20:28:59 (live play) draw
Perpetual check. Would still be a draw.

Adam (tourn.) / Jonas (tourn.). Fetlar Hnefatafl 11x11, 74 moves, 2011-08-04 22:09:58 (live play) draw
Edge fort with moving king. Would be turned into a white win.

Jonas (tourn.) / Adam (tourn.). Fetlar Hnefatafl 11x11, 44 moves, 2011-08-04 21:48:31 (live play) draw
cosinus / Hjalte. Fetlar Hnefatafl 11x11, 62 moves, 2011-07-15 21:56:44 (live play) draw
Center fort. Would be encircled and turned into a black win.

Hagbard / sea slug. Fetlar Hnefatafl 11x11, 43 moves, 2011-05-13 20:44:36 (live play) draw
Perpetual check. Would still be a draw.

Pedro / crust. Fetlar Hnefatafl 11x11, 64 moves, 2011-02-13 16:26:26 (live play) draw
Edge fort with non-moving king! Would still be a draw.

Hugues / MaC. Fetlar Hnefatafl 11x11, 73 moves, 2011-02-06 16:08:27 (live play) draw
Hugues / crust. Fetlar Hnefatafl 11x11, 31 moves, 2011-01-27 20:24:08 (live play) draw
Perpetual check. Would still be a draw.


A recent analysis on the Fetlar balance gave (2012.01.30)
Hagbard wrote:The count shows for Fetlar Hnefatafl 11x11:
16 white wins (defenders) = 44%
14 black wins (attackers) = 39%
6 draws = 17%
Copenhagen rules used on those 6 draws give:

Adam Roderich 0.5-0.5
Perpetual check. Would still be a draw.

Adam Jonas 0.5-0.5
Edge fort with moving king. Would be turned into a white win.

crust Hagbard 0.5-0.5
Jonas Adam 0.5-0.5
Hagbard Roderich 0.5-0.5
Center fort. Would be encircled and turned into a black win.

MaC crust 0.5-0.5
Draw by agreement. Would still be a draw.

which changes the 6 draws into 2 draws, 1 white win and 3 black wins

resulting in a balance for Copenhagen Hnefatafl 11x11 of
17 white wins (defenders) = 47%
17 black wins (attackers) = 47%
2 draws = 6%

Hagbard
Posts: 406
Joined: Sat Mar 14, 2015 6:07 pm

Re: About the draw concept

Post by Hagbard » Sun Feb 05, 2012 7:57 pm

The edge fort is so rare, found in only 1 out of 383 games in the games archive, that it doesn't make much difference whether this is counted as a white win or a draw. So in that sense a win-rule is superfluous. It could however in the rare cases distinguish the real master, who thus has the option to turn the draw into a win.

Image

In the diagram, black clings to the corners with only 12 men left and edges are all open, while white rules the whole board with king and 6 men. Wouldn't it be fair for black to loose this one?

Update 2012.2.5
It would take a paragraph in the rules to explain that this particular case in 1 out of 383 games (a moving king inside an edge fort) is different than other forts. Not worth it. The master would've won the game in the diagram long before the shown situation.

Adam
Posts: 115
Joined: Fri Mar 20, 2015 1:28 pm

Re: Copenhagen Hnefatafl

Post by Adam » Sun Feb 05, 2012 11:22 pm

Very interesting stuff Hagbard. Thanks for taking the time to write all that up.

I feel like i've used edge fort bunkers a lot, maybe i've tried to use them lots, to little avail!

I'm liking the new stats very much. 47% vs 47%. And if we made perpetual check into a forced play away move for those forcing the repetition, those games would presumably play on to interesting finishes. Possibly favouring black, but who knows?

I hear what you are saying about the edge fort being an end game fort. You are quite right, its a last ditch effort for white, it can require fewest men, and as you say white needs black to have developed away from the edges to makes a shot at it. Even so, with it being potentially a winning position, white may reasonably aim for that position from the start, while perhaps feigning a corner attack which requires attention and preventative measures from black, dividing his forces. However balance is restored as while white is gaining a new way to win (mobile king edge fort), Black is gaining a new way to win (totally surrounding white players away from the board edge.) forcing the king to make a break for it.

Further thought on the logic behind allowing and disallowing certain forts leads me to suggest the following refinement:

White win draw fort: Any draw fort that has contact with the board edge and a mobile king contained in its structure, the king having contact with the board edge. i.e. white has built a safe, defended escape route from the board, which would still be impenetrable with the king having escaped. Or more elegantly: If the king has contact with the board edge, is able to move, and it is impossible for black to capture him, white wins the game.

Black win draw fort: Any fort not connected to the board edge which is entirely surrounded by black pieces such that only movement within the fort is possible for white. I suggest this includes centre forts where the king is trapped at a board edge. The logic being, if he is dead inside that fort, he is dead out of it too. The assumption being that the centre fort is captured. If we remove those pieces, the king could then be forced away from the board edge and captured.

Draw draw forts. (now there is a phrase one doesn't come across every day) A draw fort connected to a board edge where the king is not mobile, including a king trapped elsewhere on the board edge (Garbo). The logic for allowing the Garbo, is that while the king is apparently vulnerable, we are agreeing that the edge fort is not captureable, so the king is safe to wait it out.

And with the addition that any repeat move that involves a checking move may not be repeated more than 3 times, at which point the checking player must make a different move. Might as well tidy up this lose end while we are at it, even if in the stats this kind of draw is rare. Its created schisms on other sites, and I've dealt these draws out and been on the receiving end, and neither is very satisfactory. Neither player feels like they've done a good enough job, hence the draw. But as the onus is on white, it should really be disallowed.

Assuming you guys think these suggestions sensible, I leave it to Hagbard with his Occam's razor to make this into a rule set that a beginner could comprehend, and not just us feinschmeckers.

Adam
Posts: 115
Joined: Fri Mar 20, 2015 1:28 pm

Re: Copenhagen Hnefatafl

Post by Adam » Sun Feb 05, 2012 11:40 pm

Hagbard wrote:The edge fort is so rare, found in only 1 out of 383 games in the games archive, that it doesn't make much difference whether this is counted as a white win or a draw. So in that sense a win-rule is superfluous.
disagree with that, once its a win, its going to form a part of whites arsenal. And while it may not appear in the stats as a draw position, fear of the bunker, the simplest of forts and an edge fort, has leveraged many a black player into some unwanted panicky moves. Fear of the bunker as a winning position would amplify this effect on black.
Hagbard wrote:In the diagram, black clings to the corners with only 12 men left, while white rules the whole board with king and 6 men. Wouldn't it be fair for black to loose this one?
Yes, but only if white can build the fort. End games like this are the nail biters demanding elegant economic play from black.
Hagbard wrote:It would take a paragraph in the rules to explain that this particular case in 1 out of 383 games (a moving king inside an edge fort) is different than other forts. Not worth it. The master would've won the game in the diagram long before the shown situation.
I really think it is worth it. Firstly, that 1/383 might jump when its a winning position, secondly, my previous point about leverage that doesn't show up in end positions, and thirdly, we are searching for a watertight set of rules worthy of an international tournament level game, and a game worth playing at that level. While not as simple as forbidding draw positions totally, I feel this solution is elegant in that it allows all the game complexity offered by draw fort leverage to exist while removing the early draw problem. I really feel like we are zeroing in on a game and rule set I would feel confident presenting to the chess federation, most likely in conjunction with a 9x9 rachuneck type game, and even also berserk if we feel its functioning well enough and with Aage's permission, though it might be jumping the gun a bit. While I at first thought the winning drawfort was a messy idea, I quickly came round to thinking it actually makes sense of the whole phenomenon!

Adam
Posts: 115
Joined: Fri Mar 20, 2015 1:28 pm

Re: Copenhagen Hnefatafl

Post by Adam » Sun Feb 05, 2012 11:55 pm

crust wrote:That's brilliant - we may (occasionally) have our concerns over draws etc, but on the subject of balance, I think Fetlar has passed the test with flying colours.
Yes indeed, and in case other readers are not aware, this point is being explored in depth under the topic of 'About the draw concept', where an intersting Fetlar variant is being proposed that solves the early draw fort problem, while allowing drawforts to continue to exist. Exciting stuff.

And to reiterate my main reason for thinking this is worthwhile in terms also of game balance, the stats white 44% black 39% draw 17% look very different when you realize that those draws are all forced by white. One might say for example, that black is preventing white from winning 39% of the time, while white is preventing black from winning 61% of the time. The new variant looks like it could be much more even in this light also.

crust
Posts: 127
Joined: Sat Mar 21, 2015 9:29 am

Re: Copenhagen Hnefatafl

Post by crust » Tue Feb 07, 2012 1:34 am

Hagbard wrote:We have Hnefatafl players very well informed in quantum physics here!
I learned it all from Richard P. Feynschmecker and his excellent books Six Easy Pieces and Surely You're Joking, Mr. Feynschmecker
Adam wrote:we are searching for a watertight set of rules worthy of an international tournament level game, and a game worth playing at that level. ... I really feel like we are zeroing in on a game and rule set I would feel confident presenting to the chess federation,
Yes, absolutely, me too. Good work everyone. Copenhagen rules remove many of the annoying possibilities which regrettably exist in Fetlar games - and make for better openings and exciting endgames (I think). I hope the balance of power has not gone too far in favour of black, though, especially if we're stripping away the leverage afforded by draw by repetitive check as well. Only testing will tell.

Great work on the figures, Hagbard. Very encouraging. And Adam your categorization of draw forts into white wins, black wins and draw draws (!) is very helpful.

Hagbard
Posts: 406
Joined: Sat Mar 14, 2015 6:07 pm

Re: Copenhagen Hnefatafl

Post by Hagbard » Wed Feb 08, 2012 11:26 am

crust wrote:I learned it all from Richard P. Feynschmecker and his excellent books Six Easy Pieces and Surely You're Joking, Mr. Feynschmecker
Thanks, I must read those; the encyclopedia says the author has a great sense of humor. At one time I attended a course of lectures on quantum physics, and it was the most long-haired mathematics I've ever seen.
Adam wrote:I feel like i've used edge fort bunkers a lot, maybe i've tried to use them lots, to little avail!
No, probably Adam remembers right. In the summer 2010 Adam, crust, Pedro, MaC, Roderich and myself had hundreds and hundreds of games to explore all aspects of the Hnefatafl 11x11 rules and other variants. (And during the process confirming the Fetlar edge rule: no one could win as white against crust and Adam without the Fetlar edge rule).
Very unfortunately all these games were not recorded, they would've been valuable material. Record of the games began only from 2010.12.23.
conanlibrarian wrote:3a. If a series of moves is repeated three times, the offensive player (i.e. the one performing a threat) must find an alternative move. (from Cartier)
Adam wrote:And if we made perpetual check into a forced play away move for those forcing the repetition, those games would presumably play on to interesting finishes. Possibly favouring black, but who knows?
...
And with the addition that any repeat move that involves a checking move may not be repeated more than 3 times, at which point the checking player must make a different move. Might as well tidy up this lose end while we are at it, even if in the stats this kind of draw is rare. Its created schisms on other sites, and I've dealt these draws out and been on the receiving end, and neither is very satisfactory. Neither player feels like they've done a good enough job, hence the draw.
crust wrote:I hope the balance of power has not gone too far in favour of black, though, especially if we're stripping away the leverage afforded by draw by repetitive check as well. Only testing will tell.
I've experienced the perpetual check as a lifesaver for white, a lucky rescue out of a situation that's beginning to look hopeless. You cannot plan for this many moves ahead, the opportunity arises suddenly. On the other hand the white luck is not entirely undeserved. The king did make it to a direct attack on a corner, and the black adversaries in the corner are too scarce, so that it depends on a single black piece to keep the king out. White will stay in this deadlock only if he judges that he's in a loosing position, otherwise he'll go on and attack elsewhere. If white were to be forced out of the deadlock, the game would go on to a miserable end for white, because white has judged that he's loosing.

This is the way the perpetual check draw is seen to be used on this site.

Repoupoune / Roderich. Fetlar Hnefatafl 11x11, 43 moves, 2011-08-11 20:28:59 (live play) draw
is an example of a game where white has a perpetual check very early in the game and chooses to continue the attack elsewhere, only to later in the game end up in a hopeless encirclement and be so lucky as to have another perpetual check! Draw.


Image
The diagram is an example that it can be possible to abuse the perpetual check draw, much like the early draw fort. The game in the diagram is not at all settled yet, and if white should decide to stop for draw here, then I suppose it wouldn't be very good sportsmanship.

- But, unlike the two-moves Monstrosity game with the early immediate draw fort, in the diagram game white has at least made an effort and succeeded in moving the king very close to a corner.

There's no way to prevent the Monstrosity game without some rule modification, whereas the situation in the diagram could've been avoided; it just was white's lucky day.

To conclude, I like the perpetual check draw the way we use it, but that's just my opinion.

Hagbard
Posts: 406
Joined: Sat Mar 14, 2015 6:07 pm

Re: Copenhagen Hnefatafl

Post by Hagbard » Wed Feb 08, 2012 10:53 pm

Adam wrote:I hear what you are saying about the edge fort being an end game fort. You are quite right, its a last ditch effort for white, it can require fewest men, and as you say white needs black to have developed away from the edges to makes a shot at it. Even so, with it being potentially a winning position, white may reasonably aim for that position from the start, while perhaps feigning a corner attack which requires attention and preventative measures from black, dividing his forces. However balance is restored as while white is gaining a new way to win (mobile king edge fort), Black is gaining a new way to win (totally surrounding white players away from the board edge.) forcing the king to make a break for it.
Here's material for many good test games! I tried against the computer, which turns out to be a bad opponent for this test. The comp plays aggressively and so the edges are very little exposed (in return it's easier to outsmart the comp and reach the corners). The edge fort is probably more relevant against a more defensive (and dangerous) opponent who shields the corners off while exposing the edges.

Image
A draw draw fort based on only two edge squares.

Image
Another draw draw fort.

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