39 votes
Accepted

Is there a balanced chess system where players of unknown skill can have an equal chance of winning?

Yes. The way I've done this in the past is to play a series of games with clocks starting with 10 minutes each on the clocks and then the rule for subsequent games that the winner of the previous ...
  • 81k
28 votes

Is there any position where not promoting (illegally) would be the best move?

Here is an example: [fen "8/4P3/8/4p1p1/2p3Pp/p4p1K/k1p2P1P/8 w - - 0 1"] 1. e8 leads to stalemate next move, while all legal promotions lose to 1... c1=Q followed by 2... Qf1#.
26 votes

On an infinite board, which pieces are needed to checkmate?

In fact K+R+R can force checkmate against K on an open board. First move both Rooks away from the King and to different rows and columns. Then check the King with one Rook, say on a row. Whichever ...
25 votes

What are the rules of Quantum Chess?

The board and pieces Quantum chess is played on a regular 8x8 chess board with standard pieces. Pieces have rings around them, filled in with colour. These rings show the probability that the piece ...
  • 2,061
24 votes
Accepted

Is there any position where not promoting (illegally) would be the best move?

The Matt Bengtson problem Prof. Elkies mentions is: [Title "Matt Bengtson, Chess Braintwisters (Burt Hochberg), no. 103. White to move & draw."] [FEN "4kn2/3p1pPp/4pPpK/6P1/8/2p5/1b6/8 w - - 0 1"]...
  • 5,820
24 votes
Accepted

Moving into check for a draw as black, why is it illegal? Comparison to Racing Kings

Imagine a variation of chess without the rules about check and checkmate, where a player wins simply when he captures his opponent's king. In this variation, Kxd5 loses the game to exd5. Turns out, ...
24 votes
Accepted

Can you solve this chess problem of a lone knight against numerous opposing pieces?

OK The check must come from the knight (D'uh!) The black king must be on c5 for the mate The white king must be used to cover any empty squares to the right of the black king - thus the white king ...
  • 4,041
22 votes
Accepted

Chess960 or Chess959?

There is no mention of excluding the regular starting position in Appendix F. of the FIDE Laws of Chess, so it's really Chess960 and not Chess959. I can imagine that there are chess programs or ...
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22 votes
Accepted

Is there a name for a chess variant where you are allowed to capture your own pieces?

In German, we would call this "Schlagschach". The German Wikipedia translates this to "Capturechess". However, I could not find an English resource that describes this variant. But there is a thread ...
20 votes
Accepted

Could two kings force checkmate against a lone king?

If these are two real kings, it is not possible. This is because one requirement of checkmate is that the black king is in check which cannot be achieved with any of the white kings, since it would ...
  • 20.5k
18 votes

Could two kings force checkmate against a lone king?

A King and a Man (or commoner; i.e., a non-royal King) can mate a lone King. The longest distance to mate on a standard 8x8 board is 18 moves. The result quoted above was obtained by H.G. Muller in ...
18 votes

Moving into check for a draw as black, why is it illegal? Comparison to Racing Kings

Those are just the rules of the game. You could absolutely try to make the case that moving into check in such a situation should be legal, but playing by those rules wouldn't be chess anymore (it ...
18 votes
Accepted

Can you castle twice in Chess960?

Excellent question. The rules state that this is not possible. Castling can only be done once. This is explicitly mentioned under Guidelines II. Chess960 Rules: II.3.1 Chess960 allows each player to ...
  • 5,575
17 votes
Accepted

What are the best openings in Antichess?

It was discovered that e3 is a win for White: http://magma.maths.usyd.edu.au/~watkins/LOSING_CHESS/ICGA2016.pdf
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17 votes

Moving into check for a draw as black, why is it illegal? Comparison to Racing Kings

I will answer from a different perspective: why Racing Kings (RK) has a rule to allow black a chance to draw, and why the same logic doesn't apply to chess. What is Racing Kings (RK)? Background for ...
  • 4,910
16 votes
Accepted

On an infinite board, which pieces are needed to checkmate?

Here are some mates I found: Queen and rook (limit the black king until the white arrives to help) [Title "KQR vs k mate"] [FEN "1R6/5k2/8/8/8/8/6Q1/K7 w - - 0 1"] 1. Qg8+ Ke7 2. ...
  • 3,531
16 votes
Accepted

Would bishops be stronger or weaker on the same coloured squares?

And the correct answer, as always, is: "it depends on the position" :-) OK, assume that you start with Bb1/Nc1. Lichess says +0.1. But this is the sum of... the N generally standing a bit ...
15 votes

What are the best openings in Antichess?

I cannot really speak from my own experience, but there seems to be some very decent sites about Antichess. Here is what this one has to say about the opening: "Just like in chess, the main goal in ...
15 votes

How would the min max algorithm of a chess engine work in the case of 3 player chess?

The problem is really not in chess, but in any naive 3-player version of any 2-player strategy game. In general, it is hard to make an interesting 3-player game where each player's performance is ...
  • 2,543
13 votes

Can one side force a loss in regular chess?

There is likely not a way to force a loss. Selfmates are relatively rare, and one can probably not be forced from the opening position. The best plan, paradoxically, is likely to try to capture as ...
  • 15.8k
13 votes

On an infinite board, which pieces are needed to checkmate?

An infinite number of knights would be insufficient to force checkmate, assuming the enemy king starts some distance away and not surrounded. The knights are too slow and not enough of them can chase ...
  • 15.8k
13 votes

Would bishops be stronger or weaker on the same coloured squares?

Are you familiar with the variant known as Crazyhouse? Basically, if you capture an opponent's piece, you can spend a later turn to place it anywhere you like on the board, as your own piece. This ...
12 votes

Who wins in the game "knight" if both players play optimal?

In my answer to the same question over on math.stackexchange, I discussed general m by n boards. Here I will just give a winning strategy for Player 2 on the ordinary 8 by 8 chessboard. It's based on ...
  • 3,256
12 votes
Accepted

Checkless Chess

Your "checkless" chess AI would run into problems with the stalemate rule. It would consider the poaition with white king on a6, white pawn a7, black king a8, a win for White because wherever Black ...
  • 3,256
12 votes
Accepted

How do computers play three-check chess?

https://github.com/ddugovic/Stockfish Very active development, this is the Stockfish version used by lichess. What you need to do is search this macro: #ifdef THREECHECK Evaluation function: ...
  • 21.6k
12 votes

How do computers play three-check chess?

I have been working on the aforementioned code of Stockfish for three-check chess, so I will try to summarize the most important evaluation changes (in terms of Elo gain) we made compared to standard ...
12 votes

Is there a balanced chess system where players of unknown skill can have an equal chance of winning?

A common way to have a large number of weak players have a chance at beating a single strong player is simultaneous chess: image taken from http://www.chesshistory.com/winter/winter89.html The ...
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12 votes
Accepted

How many moves of head start does white need for a guaranteed win?

There is a similar ancient question, but this isn't a duplicate since White may move anywhere. For an upper bound, I can prove a guaranteed win for White in 5 moves. Indeed, it is reminiscent of ...
12 votes
Accepted

In Hand and Brain chess, is the stronger player generally preferred to be the hand or the brain?

Not a definitive answer, but I'm posting my comment based on the upvotes it received. It depends. GMs have different opinions. GM Hikaru Nakamura has said it really depends on the situation. ...
12 votes
Accepted

Elo disadvantage due to one pawn move in Indian Chess

Revised stockfish to skip searching double pawn push. Each engine is using 2 threads at TC 1m+1s. It got 4 draws in 20 games. Test 1 sf_no_pawnpush4 is not aware that its opponent can play a double ...
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