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It sounds like perhaps you're misunderstanding the rules. Each turn a player attempts to make a move as usual. If the opponent wishes, they can force the player to retract that move and make another.

What you describe sounds like No-Chess
http://www.chessvariants.org/other.dir/no.html
For that game, I think the answer to your question should be "yes". In particular, white can "refuse" some impossible move.

I don't think so. The variant I'm referring can be found in Variant Chess
magazine, issue 1.

In that variant, each player refuses a possible next move of his opponent
while making his move.

Okay, you got me to dig out my complete set of Variant Chess issues. 

First: Refusal Chess [article by Paul Novak]

"Refusal Chess (also known as Rejection Chess or Outlaw Chess) was invented by C.H.O'D, Alexander... The only rule change from normal chess is that you may refuse one of your opponent's moves each turn (you cannot leave your king in check though and refuse your opponent's piece takes your king).

Since its conception two very similar siblings have appeared; that the number of refusals is limited; and where two moves are proposed together on each turn... 

Different pawn promotions count as different moves..."

So there is a confusion among similar games, which is causing the problem.

Based on my reading of this, a player may or may not refuse a move. So white is not obligated to refuse a move of black's. But black has the right to refuse white's move R-h5+. So white must make a different move. Still, any rook move on the H column would mate, except of course, R-h7. 

This does indicate a problem - if white did play R-h7+, could white then refuse k x R, leaving black no legal moves at all, and if so, would it be considered stalemate rather than checkmate? It's maybe slightly shaky logic, but not totally outside the realm of possibility.

In this game to me KNB vs K doesn't seem a forced mate anymore, but I have not checked yet, does anyone know better? Anyway if not so, many other like usaual close wins may not be. Point being the game is more drawish, maybe a rules may be made that you cannot refuse a checkmating move, or something on those lines. I doubt that is in the spirit of the game though :(!

The rules are not unambiguously specified, w.r.t. checking. In FIDE rules it is not legal to expose your King to capture. But in Refusal Chess, do you expose your King to capture when you move to a square that is singly attacked by the opponent? I would say "no", because you can always refuse the move that captures it, and so there is no danger to your King. An alternative is that you lose the right to refuse after your King is captured. Then Refusal and orthodox Chess have the same legal moves.

Under these rules even KRK would seem a draw, as there always is only one way in that end-game. (The Rook has to check along the orthogonal that contains both squares ot covered by the attacking King, and a Rook can always reach a given orthogonal in only oe way.) This makes the game very drawish. I therefore think it was a mistake to adopt the rule that you cannot refuse the opponent's only legal move; it would have been better to make that a checkmate or stalemate, depending on whether he is in check. That makes checkmating easier, rather than more difficult. It still does not seem too easy, as you still have the option to refuse a move that would put you in a position where you only have a single legal move. That is, you never really have only a single option, as you always have the choice to make that move or refuse the opponent's previous move. Another ambiguity is what happens when you have no legal move at all. Are you forced to refuse then, or does it count as stalemate?

Yes, you pointed out many problems, but I think this game brings an interesting concept, espeacially for middle game (in the opening there are usual many sensible options). I also believe that the larger the board and army size the cocept gains in complexity as there are more moves to choose from. Anyway something has to be done about the endgame. If all balanced games end up in draws what's the point?

Does anyone know how well a chess engine will play this game against a human?

It's not convenient, but this game can be played against an engine by setting the engine to its strongest level, then letting it play a move. If you refuse the move, then you make the engine go back, and play a different move (temporarily setting to a lower level, until you find the engine's "2nd" best move).

The computer will reject your moves by checking if they are "best" or not.

To me it seems that in a chess opening to the mid-game, there are enough move options that the computer's "2nd best" moves will always be very good - better than most human players. Therefore the board position will start to favor the computer.

In an end-game, the engine may falter - because it will not play well knowing that the best move will likely be refused. But to get to the end-game, the computer may already have achieved a formidable advantage, and the human player will already be in a hopeless position.

I tried this once, and couldn't find a flaw with this type of strategy (from the computer's point of view). But I only got to about 8 moves, and then stopped the experiement. The computer was in a winning position, but this was winning as judged by normal chess - not refusal chess. So I could not say for sure the result was conclusive.

I'd like to try again, but am already busy in other games. Can anyone predict (or know) the result if taken to its conclusion?

I'm not sure if it is the actual game but as someone who tried a bit chess programming I can say it is doable, it is just a matter of optimizing the 2nd move rather than the first. The main problem is that we should, as a community come up with better rules, I myself will soon start (I hope) other things, in my apothecary chess series. So I can't  actually study this bit but the idea seems promising. My belief is that it needs polishing. V. if you'd like you may post a challenge and we should try together (actually I prefer 2 as I find this game promising). All that if there is a game courier version.

A normal Chess engine should play this game disastrously poorly. It would be very easy to trick it. E.g. it will suppose its pieces are sufficiently protected when they are once protected, and attacked only by a single more valuable piece. E.g. wait until he moves up a Knight, protected by a Pawn. Than attack that Knight with your Queen. The engine will ignore it. It will also think QxN will not be your best move, as it sacs a Queen. So it will let you play that. Then it will try to recapture PxQ, and you refuse that. Bye bye, Knight. Repeat for the other Knight. And then Bishops...

It should indeed be very simple to modify an existing engine to play it. Just make it keep track of the score of the best two moves in each position, rather than only the best, and take the score of the second move as the score for the position. This will need a pair of moves to refute a line, rather than one, so it will increase the branching ratio by a factor sqrt(2), so you will lose some depth. To optimally use a transposition table it will have to hold the pair of refuting moves, rather than just the best. This shpuld be pretty trivial.

HGMuller, how far into a game will that be evident? I didn't detect anything like that happening in the first 8 moves of a simulation that I tried.

(In the example you provided, you say "...attack that knight with your queen. The engine will ignore it." This may be optimal play for the side with the engine)

I certainly believe an engine (as described previously) will falter at some point, but wondering how far into a game is it expected?

For me nothing was evident in the early stages. I could not find a way to out-smart the engine in the opening phase of the game.

Aurelian Florea, I also noticed you offered to play a game. If you'd like, we can do an experiment.

It's not human vs. human. It will be you (human) vs. computer (me).

I will always choose the best move by computer. If you refuse, then I'll play the 2nd best move (also by computer).

Let me know if you'd like to try that. I haven't played any game here on the courier(?) system, but I'm sure it's not too hard.:)

@V.

If you say you would just plug in engine moves, than it wouldn't be that nice would it. Anyway my point was that this game has a slightly different strategy. You should try the game courier it has plenty of nice games and I have plenty of already on challenges. Otherwise you may challenge me directly, my user name is catugo.

I agree that playing your own moves against an engine removes the "competitive" spirit. From my side, I would need to run an engine a few times at each move to learn its 1st and 2nd best moves - but still is not a lot of work on my part.

The idea was an experiment. It would be to test the theory that an engine would play "disastrously poorly". I've seen this discussion of human play vs engine for Refusal chess more than once, and (so far) I have not seen a human willing to go against the engine.

(btw: thanks for your offer - If I played a game against you it would be Enep. That sounds like a fun one too!)

Ok, we can do it, just plundge in maybe even 2 challenges (1white,1black), but I doubt an engine that is not purpuselly desingned for that will manage. But with you assitance situations like when only  one piece attack your queen, will be ignored.

H.G.

Will you kibitz from time to time? I agree with what you said about modifying an engine :)!

Note that engines nowadays almost all have a 'Multi-PV' mode where you can directly ask it to show the best N moves.

In the opening there is not much tactics. This is almost the definition of 'opening'; you just develop your pieces before actually hostilities start. I am perhaps 1500 Elo weaker than Stockfish, but it would not cause me any trouble at all to still be in an almost equal position (or slightly better, if I had white) after merely 8 moves. That is no matter of the quality of play at all.

While at the local supermarket cue, I got on thinking. So even in the opening it could matter. Think about fianchetto-ing your bishop: you move your b or g pawn and then your opponent keeps refusing your bishop move. On the other hand your king pawn opening seems to gain merit, think about the scandinavian, 1.e4 d5 and then you can merely move 2.c4 for example (not sure if it is actually good) as you can always refuse the capture. Point being it is not just choose the second best move, every move has new posibilities. I honestly think this game is more strategic than tactical by comparisson the orthodox chess, or at least is something else both strategically and tactically despite the state space of the game being the same :)!

Ok awesome, to my knowledge, Aurelian is the first person in the universe willing to play Refusal chess against an engine - a historical landmark! I think we only need to play one game for this experiment. If Aurelian plays White and wins, then he has outsmarted the computer.

I've never played a game on the game courier here before, so I hope I did everything right. I set up an invitation here:

(I hope to play one move per day, but might miss a few days. I do have some travel planned this month that might slow things down for short periods.)

Game has started well so far, but no move has been refused yet. I'm sure it will happen soon. I didn't think about it, but I'm not even sure if the game courier allows take-backs. If there is no way to refuse and take back moves we'll have to find another way to do it. We'll see how it goes.:)
 

I just refused a move, so you need to take back (just browse through and redo the last move). Trouble is with that preset there is a ban on the "pass" instruction so I just offered a draw you should not accept :)!

When I go to the game, it says "Drawn Game" and I do not have any options to do anything. (I haven't played a move, or accepted the draw, or anything).

Is there a way to take back my move (since you rejected it)?

All we need is a system to show a board diagram, and I'm wondering if there is an easier way to play this.

As this is normal Chess, you could use my turn-based server, which has it already set up as a demo. Because there is no rule enforcement, it is ideal for refusing moves: you just take back the move the opponent just did, so he can play his second choice.

I am ok with that but as my chess skills are very low, I'm not sure if I am the correct person for this experiment, anyway V. if you still agree we may try this way :)!

HGMuller,
I can move the pieces and set-up the board to the current position, but I don't know what to do to save it.

I already have a username and password. The opening window shows a conversation between you and "jon".

So my two questions:
1) how do a save a position?
2) how do I clear the conversation, so it's a fresh board for Aurelian and me?

This may work, but having trouble with some basic things.

So my two questions:

1) how do a save a position?
2) how do I clear the conversation, so it's a fresh board for Aurelian and me?

You 'save a position' by pressing the 'Play Move' button. This only works if you are in a game, though. So you first have to start a game, or recall a previously started game (that is still in progress). Once a game is loaded, and you are on move in it, you can move one or more pieces, and when you are happy with it, press 'Play Move' to submit all the moves you added to the game to the server, as a single turn. In Refusal Chess you should only move a single piece, undoing the opponent's last move if you want to refuse it.

The conversation is only there because I used that page also as a demo for broadcasting comp-comp games, to offer the people watching them to discuss about the game. I agree that it is less applicable when the page is used for depositing their own games, and there is no concept of 'the current game'. But you can just ignore the chat; it is not part of your game, just a general medium for all users of the page to coverse with each other. And as for the time being you would be the only users (I have no plan for broadcastig anything), you could use it as an open (volatile) communication channel.

BTW, when I press 'List Players', I don't see your name. So if you tried to register yourself, you did not succeed.