Re: Copenhagen Hnefatafl
Posted: Thu Mar 08, 2012 6:20 pm
Here white attacks on a full line, and black must use not one but several pieces to block.
Discussions on the Viking board game Hnefatafl
Crust and I have a had a discussion about all these latest perpetual check considerations and I think we have made some headway, pretty much where Evans was heading in that last paragraph. Here is a summary:crust wrote:But is it repetitive check?
This poses an interesting problem. I think in practice black would have long since trapped the lone king. But of course in this position black can easily refuse to try to capture the king thereby forcing a stalemate. But trying to capture the king would quickly degenerate into perpetual check forced by white, so with Strong Copenhagen rules, it would be in blacks interest to go after the king anyway and certainly win.Hagbard wrote:
In the end game, this situation could happen: both white and black lost 12 men, and left is the lone king and just enough blacks to block the corners. If the game ends as shown in the diagram, shouldn't this be a white win? The king did escape to the edge, can move and is not captured. Maybe he can be captured, but we'll never know, because black doesn't try, so the king is as safe as in a fort. If black should try to go after the king, the king would probably escape to a corner.
Strong and weak copenhagen interpretation...Adam wrote:Following the fun science references, Crust and I have been referring to the rules now being tested on Aage's site as the 'weak' copenhagen interpretation, and a version forbidding perpetual check as the 'strong' copenhagen interpretation. Otherwise the rules are the same.
The examples involving several pieces and movements on full rows, or even complex repetitive movement patterns several times around the whole board as indicated by crust's puzzle, show that a perpetual moves situation cannot be detected simply by counting the number of side steps done by some piece.Adam wrote: Any "preventable mate in 'n'" threat that involves indefinitely threatening mate in 'n' where the 'victim' is forced to respond but where the aggressor cannot achieve checkmate is to be abandoned by the aggressor if each preventable mate in 'n' position has been shown to fail a maximum of 3 times.
So Hagbard's last example has, as far as i can see at least 8 mate in 'n' positions (assuming black moves as economically as possible to prevent opening more of the 9 possible mate in '2 or 3' options on B to J, and the 2 mate in '1' options on A and K. Meaning white is free to explore all those possibilities, but as long as the two players are aware that black will always block, they both know its a waste of everyone's time and energy to pursue the attack.
If white has other pieces, white must be allowed to use the check leverage to position blacks pieces as they choose, before bringing in reinforcements, but three repeats of each attack position is ample to allow for this. However, if this is not whites plan the rule is simple enough, white is making essentially the same threat, so at some point they have to move another piece or play a non checking move with the king. How you program that I leave to Aage!
As for Crusts 'windmill' puzzle, I don't see any problem here either. Each corner attack position is a self contained "preventable mate in 'n'" situation. One simply applies the 'no more than three repeats' rule to each situation. If someone is cunning enough to come up with a "preventable mate in 'n'" chain that carries us around the board and back to the original board set up, the rule can still be applied as you are then repeating a series of identical board set ups. You cant go around the board more than 3 times.
As for the 'who started it?' problem, this is an illusion. Any situation that presents a repeating board pattern, can always be easily traced back to who started it, even a complex series of moves that lead us back to the original board position. It will always be self-evident which player made the first move in the repeating pattern.
conanlibrarian wrote:Also, I think you are to "infected" by the modern chess rules, look at the rules for Xiangqi and Shogi (Chinese and Japanese chess). They both have rules for breaking perpetual threat situations quite similar to the proposed rules above.
What about adding a "strong version" of a perpetual moves rule to the current tournament:Evans wrote:If we do find a rule though that is able to be clean and best for both corner Tafl and edge Tafl as well, then I would not complain! But my suggestion was more for corner Tafl.