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        Arimaa >> General Discussion >> Endgame Puzzle 2
        
(Message started by: jdb on Mar 30^th, 2011, 9:00am)

Title: Endgame Puzzle 2
Post by jdb on Mar 30^th, 2011, 9:00am

Gold to play and win.

1w Ra1 Cd1
1b rb5 rd5

Added to arimaa puzzle collection:
http://arimaa.com/arimaa/puzzles/show.cgi?p=p60

Title: Re: Endgame Puzzle 2
Post by rbarreira on Mar 30^th, 2011, 9:14am

This time I won't post the bot analysis early, maybe more people would be interested this way...

Title: Re: Endgame Puzzle 2
Post by RonWeasley on Mar 30^th, 2011, 9:57am

I like it when you include the planning app link. http://arimaa.com/arima/games/planGame.cgi I am too lazy to find this on my own.

Title: Re: Endgame Puzzle 2
Post by robinz on Mar 30^th, 2011, 10:14am

I think I've got it, but, as there seems to be no option to hide text on this forum, I won't say anything here so as not to spoil it for others. (I'm also far from certain I'm right, being a pretty weak player compared to most forum posters ;) - but my solution seems to work, and all others seem not to.)

I'm pretty sure nothing like this could ever come up in a real game (even allowing for the fact that the position would be identical were the cat replaced by any non-rabbit piece), but it's a fun puzzle nonetheless. I hope for more :D

Oh, and the planning link is: http://arimaa.com/arimaa/games/planGame.cgi (thanks Ron for posting it, but you missed out a vital "a" ;))

Title: Re: Endgame Puzzle 2
Post by arimaa_master on Mar 30^th, 2011, 10:23am

on 03/30/11 at 09:00:37, jdb wrote:

Gold to play and win.

1w Ra1 Cd1
1b rb5 rd5

Wow not so easy - took me about 10 minutes just to find out the first move and if I am not mistaken I see Immobilization at 5w.

Title: Re: Endgame Puzzle 2
Post by robinz on Mar 30^th, 2011, 10:26am

Hmm, that makes me think that my solution must be wrong (although if so I still can't see how). I have just one move for Gold, after which Silver has many options but all lead to a loss in the short-to-medium term, as far as I can see. I certainly don't see any immobilisations (although it's possible that gold could get that option, depending on how silver plays).

EDIT: I'm now so convinced of my solution that I have PMed it to jdb :)

Title: Re: Endgame Puzzle 2
Post by lightvector on Mar 30^th, 2011, 11:42am

Oooh, cool.

This puzzle has uncovered a minor bug in sharp's handling of winning/losing evaluations and the transposition table. The bug can't make sharp miss a winning move, but it does make sharp confused about how many steps it takes to win (or lose). Fixing time!

Title: Re: Endgame Puzzle 2
Post by Fritzlein on Mar 30^th, 2011, 2:48pm

Thanks for another cute puzzle, jdb. I think I have it, but how to verify? The forum seems less suited to presenting puzzles than Omar's puzzle tool. The puzzle tool includes the plan window automatically, and conceals the answer until you are ready for it. From the forum one must cut and paste into a plan window, and if the answer is posted it is a spoiler, and if the answer isn't posted then solvers are left hanging.

May I suggest creating the puzzles in Omar's puzzle tool and linking them from the forum to create discussion? If you are avoiding the tool because it is too much hassle to use, do you have any objection to someone else adding the puzzles to the collection on your behalf?

Title: Re: Endgame Puzzle 2
Post by jdb on Mar 30^th, 2011, 2:53pm

on 03/30/11 at 14:48:47, Fritzlein wrote:

I can try the puzzle tool. I guess its ok to include the solution right away?

Title: Re: Endgame Puzzle 2
Post by Fritzlein on Mar 30^th, 2011, 3:02pm

on 03/30/11 at 14:53:32, jdb wrote:

I can try the puzzle tool. I guess its ok to include the solution right away?

Absolutely. You are expected to include the solution; the tool conceals the solution until the solver asks for it. You can also enter a hint which is concealed unless requested by the solver; puzzle creators vary as to how much they like to give away in the hint. If you really want to see how it works before creating your own puzzle, try solving a few first: http://arimaa.com/arimaa/puzzles/list.cgi

Title: Re: Endgame Puzzle 2
Post by Manuel on Mar 31^st, 2011, 3:18am

Nice one!
The solution of puzzle 2 makes me understand why my solution of puzzle 1 was not working. Interesting construction with the rabbits!

Title: Re: Endgame Puzzle 2
Post by chessandgo on Mar 31^st, 2011, 6:35am

Nice puzzle indeed. Number 2 seems easier than Number 1. The last step of 3g in the solution is rather non-intuitive, but the more intuitive move doesn't win more quickly. If things are editable, changing this last step might make the reader less confused though :)

I like the 4th/5th row confrontation. Although the puzzle is not realistic, it nicely emphasizes how important rabbit advancement is, with tense positions arising with equal advancement.

So the morale of the story is that Cat versus rabbit is a win for the cat when they play on 2/3 of the board. If I'm not mistaken, if the position was just Cd1 / rd4 with silver to play, wouldn't silver win by repetition? So that Cat < 4th line rabbit when played just with the center + 1 wing, but 4th line rabbit > Cat when played on a full board?

Title: Re: Endgame Puzzle 2
Post by Fritzlein on Mar 31^st, 2011, 9:39am

I also thought puzzle 2 was easier than puzzle 1. Once you have stalemated the b5 rabbit you can forget about it and concentrate on the cat versus rabbit showdown to verify the win. Indeed, now that I see the full win for puzzle 1, I realize that I hadn't actually verified it; Gold had a defensive resource that I overlooked to prolong the loss, so I had seen the key move without entirely seeing why it worked, i.e. without finding the move 4s that is needed to convert the win against best defense.

Title: Re: Endgame Puzzle 2
Post by mistre on Apr 4^th, 2011, 12:04pm

I quickly figured out the first move for gold and the obvious reply for silver, but I didn't figure out the remaining moves of this puzzle without looking at the hint.

For example, why is silver's best move to only move the rabbit 2 squares west and not back to d5?

Title: Re: Endgame Puzzle 2
Post by robinz on Apr 4^th, 2011, 1:30pm

I think that there is no obvious "main line" after gold's first move - it's not clear what silver's best move is, but it can be seen that everything loses for silver. The b5 rabbit must forever remain in place to prevent goal, so it's effectively his remaining rabbit against gold's cat, which gold obviously wins.

You make a good point that, rather than the move 3b given, silver could move the rabbit all the way back to d5, and will win the ensuing repetition fight if gold moves the cat back to d1. But I think gold can do better on 3w - move the cat to g2 instead of h1. This also prevents goal, while also advancing the cat. I don't think gold can be prevented from eventually freezing the second rabbit with the cat (or even capturing it outright if gold chooses to).