In Bughouse can you claim a draw if the position on the board repeated three times but the pieces available to place were different? In Bughouse chess can you make a triple occurrence draw claim if the position on the board has been repeated three times but the pieces available to the players to place were different each time?

Not having a governing body for bughouse, the rules are a little informal.

Per the Wikipedia article:

  Depending on (local) rules threefold repetition applies, in which case
  the reserve of pieces is not taken into account.

If you think about it, if the available pieces were taken into account, first, with no scoresheet, it would be really hard to prove, especially at a typically fast time control; and second, the simple mathematical possibilities would probably render any chances of a draw virtually impossible.

So basically, if the house rules allow for a three-fold repetition, it probably has to be just considering what is on the board of just one of the two boards.

So to answer the base question, most people probably play by those rules, and thus, the answer would be "yes, you can claim a draw under those circumstances".


How does the "French Defense, Winawer Variation, Fingerslip Variation" get its name? Why is this particular iteration of the "French Defense, Winawer Variation" called the "Fingerslip Variation"?

[fen "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
1. e4 e6 2. d4 d5 3. Nc3 Bb4 4. Bd2

According to "The Batsford Guide to Chess Openings" by Leonard Barden and Tim Harding:

"This move had its introduction into master play as the result of a fingerslip by Alekhine against Flohr, at Nottingham in 1936. He had intended 4 P-K5 P-QB4 5 B-Q2, but played the moves in the wrong order"

The game is at

http://www.chessgames.com/perl/chessgame?gid=1008345


How do chess openings work? A recent question by xaisoft got me thinking about a problem I had as a novice player. When I first started to play chess, I thought that the moves in an opening were independent of the moves made by the other side. For example, so long as white played 1. e4 I could play the Sicilian Dragon regardless of White's second move.

So my question is, how would you explain to a complete novice what the objective of chess opening book moves? Not a specific opening but just the concept or idea of a chess opening in general.

I'm not so much looking for an explanation of opening principles, but more about about how chess players use the openings in their games.

In improvisational music, like jazz for example, the musicians will play a song that has been composed in advance, but by choice they go "off-script" and, cooperatively, make their very own creation in the moment, guided by the structure of the composition but nevertheless doing something distinctly new with each performance. In order to do this well, and create something of beauty that actually sounds good, jazzers need to have a solid understanding of how and what to play; in a word, they need to know what moves make sense, among the essentially infinite possibilities that are available to them, within the musical context that they're in. Far from being "mere" players of the music, they are composing on the spot.

Something similar - though different in important ways - happens when two players sit down to play a game of chess. The most notable difference of course is that here, unlike the musical setting, the play is competitive rather than cooperative. That is why there comes a point in every chess game where one is forced to improvise. You can try coming in with a pre-composed script that you want to play, but your opponent most likely isn't going to play along. Each player will have to compose his or her half of the game on the spot.

You can think of a chess opening that has its own name and well-known variations much like a good song with its musical score. Through much playing, it has stood the test of time (both on the White side and the Black side) and is recognized as something of worth. In this sense, such openings are a good thing for a chess player to become familiar with. (Consider this: would you rather listen to music made by someone who's already absorbed a lot of other music, or someone who's never heard any before?) But just as someone who has done nothing but memorize the scores of a few good songs would be at a loss if asked to compose a great new piece, a chess player who has focused too much on memorizing opening lines will continually run into points where he's at a total loss as to what to do.

In each case - the composer and the chess player - what is truly useful for future performance is to seek an understanding as to what makes the individual components of a song/opening good or bad, and how they fit together to work toward a common goal, be it an aesthetically pleasing piece of music or a won game of chess. To make one's own worthwhile creations, it is more important to know how to find one's own way than just to know what others have done in the past. But the latter kind of knowledge can definitely help with the former, as long as one focuses on the ideas and principles underlying the moves, rather than just the moves themselves.

As an addendum, here is an illustrative example of how not to use book knowledge in one's games. During a 1988 tournament, a strong GM was about to have a game as Black, and was skimming through the latest Informant for some up-to-date theoretical information. There he found a game in the Petroff Defense, in which Black managed to secure a draw, that featured what was listed as a theoretical novelty (TN) on move 5 for Black. Without thinking much about the value of the move, our intrepid GM decided to give it a go himself. The game played out so:

[FEN ""]
[White "Alonso Zapata"]
[Black "???"]
[Result "1-0"]

1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. Nc3 Bf5 6. Qe2 1-0

Black is going to lose a piece, so he decided to resign. What had gone wrong? Well, the game that had slipped into the Informant had in fact been a pre-arranged draw between GMs Tony Miles and Larry Christiansen, in which they each mindlessly played out some moves and shook hands:

[FEN ""]
[White "Anthony Miles"]
[Black "Larry Christiansen"]
[Result "1/2-1/2"]

1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 Bf5 6.Nxe4 Bxe4 7.d3 Bg6
8.Bg5 Be7 9.Bxe7 Qxe7+ 10.Be2 Nc6 11.O-O O-O 12.Re1 Rae8 13.Qd2 Ne5
14.d4 Nxf3+ 15.Bxf3 Qd7 16.c3 b6 17.Rxe8 Rxe8 18.Re1 Rxe1+ 19.Qxe1 Kf8
20.g3 ½–½

If our strong GM had spent even a few moments thinking about the why of the "script" he'd just glanced at, he never would have played as bad a move as 5. ... Bf5??. Note too how important it was for White to be ready to improvise; Black's fifth move is so bad that White couldn't have expected it to be played, but when it was, White rightly sensed that something was off about it, and duly found the appropriate punishment. The moral of the story: even the strongest of players need to be careful not to rely too much on book "knowledge." It all ended well for our hero though, as he now enjoys the title of world champion.

Zapata - Anand (Biel 1988)


How does a USA chess player get invited to a chess tournament like the China-USA Chess Summit (2013)? How does a USA player get invited to such a tournament if it were to happen again? If I were to make a goal to play such a tournament what steps would I have to take? Just curious on how the registration process works since tournaments involving more than one nation seem to be closed compared to regular tournaments in the US. It would be really helpful if someone could explain how you register or get invited for either country involved.

The participants, at least on the US side, were roughly the level of players that are generally expected to play in the US Championship, although the top few players (at the time, Nakamura, Kamsky and Onischuk for the men and Krush, Zatonskih for the women) did not take part. That would imply that if you're male, you would need to be a solid grandmaster, and if you're female, probably 2200 FIDE at least. My hypothesis is that the USCF went down the list of US ratings from the top until they found enough willing players to fill their roster.

Becoming a GM is extremely difficult and you need more motivation than being able to play in a single tournament. If you're female, 2200 FIDE (about) is easier but will still require years of effort depending on your current skill level.


what are some good openings with a trap to play *against* beginners? For instance, I consider the Queen's Gambit to be such an opening. Most beginners playing black would accept the gambit, and try to defend their pawn too, leading to inferior lines for black.

Any others?

There is none. You should play the openings where you are stronger, and you should play normally as if you were facing a strong opponent, because if you let your opponent get some kind of messy position you are risking losing yourself.

All I can say is to play good moves, sooner or later your opponent will blunder something.


Can the Black still win the game? How? It’s Black to move.

[FEN "r3k2r/pppbn2p/4p1p1/8/3PNq2/2PB2P1/PP3P1P/R2QR1K1 b - - 0 1"]

Here's a picture of a groovy little portable chess set with the position above

Black is pretty well busted.  His minor pieces are inferior to White's. His Queen has few squares and will end up on f7, f8, or h6. He has not yet castled.  Plus he's down a pawn and has an isolated e-pawn whose weakness is accentuated by the uncastled King.

White has a grasp on the center, good pawns, a castled King, and a Rook on the best file. I don't care for the fianchetto'd g-pawn with the light-squared Black Bishop and Queen on the board, but if Black can't exploit it then it does not matter.

Stockfish isn't very excited about Black's chances and believes the game to be decisively won by White:

[FEN "r3k2r/pppbn2p/4p1p1/8/3PNq2/2PB2P1/PP3P1P/R2QR1K1 b q - 2 2"]

2... Qf7 3.Qb3 O-O-O 4.Ng5 Qf8 5.Nxe6 Bxe6 6.Rxe6 Nc6 7.Ba6 bxa6 8.Rxc6 Rd6 9.Qc4 Rxc6 10.Qxc6 Qe8 11.Qxa6+ Kb8 12.Rd1 Rf8 13.d5 Qe7 14.Qb5+ Kc8 15.Qc4 Qd6 16.Kg2 h6 17.Qe2 Kd8 18.Qe3 Qb6 19.Re1 Qxe3

With a score of +4.2.  None of those moves look too hard to find, and I'd wager White can find good moves easier than Black.


What are the average Elo and USCF ratings? I'm not sure if there exists an average, but what could be considered an average rating range in these systems?

I took the following data from the September 2013 Golden Database1 and "active" players are players with a USCF membership expiration date later than January 1, 20132.  All ratings are regular ratings.  Note that players have an established rating after completing 25 games.

USCF Active Players

Established Ratings

46,574 Players
1315.99 Mean Rating
1390 Median Rating

Provisional Ratings

33,692 Players
537.09 Mean Rating
410 Median Rating

All USCF Rated Players

Established Ratings

252,989 Players
1165.77 Mean Rating
1148 Median Rating

Provisional Ratings

303,153 Players
631.46 Mean Rating
576 Median Rating

Distribution of active, established USCF ratings

Note that unrated players were discarded and that no checks were done on the data (duplicate entries, placeholders, etc.).

Distribution of ratings by age

This image comes from the uschess forums.

1: The Golden Database is a database provided to USCF affiliates and TD's that includes the names, ratings, and expiration dates.  It can be downloaded from the USCF website
2: I picked January 1, 2013 as an arbitrary cutoff date.  If there's a better and easy check for whether or not a player is active I'm happy to add additional data or update these stats.


Is checkmate possible in knight vs knight pawnless endgame? I see plenty of information stating that a Knight and King vs a King is a Draw because a mating position is not possible.  I also see that it IS possible, no matter how unlikely, to acquire a mating position with 2 Knights, therefore that would technically NOT be a Draw.
I would "assume" a Knight vs a Knight (no pawns) is also a Draw, but I don't see that stated anywhere.  Does the extra Knight on the board allow for the possibility of a mating position?  For example, somehow blocking it's own King in.  If so, does anyone have an example?

Yes, it is indeed possible :)  I'll give you the coordinates for the pieces in a possible mating position, and you can set it up on your chessboard.

Place the White King on g6.

Place a White Knight on f7.

Place the Black King on h8.

Place a Black Knight on g8.

6nk/5N2/6K1/8/8/8/8/8 w - - 1 1

In that position, Black's King is checkmated.  Although, I doubt even the biggest beginner would ever let that happen to them :)  You would only be able to checkmate in that endgame if your opponent literally played the worst moves multiple times in a row.


Generate Simple Mate In 1 From Tablebases (for kids) I was trying to find a kid's app for chess that has some incredibly simple problems. However, all the apps I found had rather tricky problems. So I thought I would download 3 piece table bases and use SCID (or grep, if necessary) to create a 3-piece Mate-In-One tablebase PGN. Then just use that in iChess or any other problem app that allows PGN imports.
Much to my chagrin, the tablebases aren't in PGN format as I expected (and I cant even read them in a text editor. Guess I really misunderstand how these tablebases work).
Any solutions out there?

It's possible to generate mates in 1,2,3 etc with tablebase, but that's probably not what you want. You should understand:

You will need good programming knowledge
You will need a week generating 6-men tablebase mates
You will generate too many mates than you can possibly study

If you are confident in programming, you can do this:

Modify the Gaviota tablebase generator (ask the author for source code). Find where it calculates distance-to-mate, if it's one (or two or three), print the position out.
Modify the Syzygy tablebase generator. Syzygy reports distance-to-zero, so you may need to use online probing (e.g. Nalimov) or an engine.
Use the public API in https://syzygy-tables.info. Start from a randomised position. Use the API result to move your position to mate-in-one.

If you don't have any idea what I'm talking about, generating mate positions with tableabse is not for you. You should:

Buy a book with mate-in-one positions. There is an Android app that can read a chess diagram and convert it to PGN.

EDIT: You shouldn't generate total random FENs. You should try to generate FENs that either side has an extra rook, queen etc.


First known computer-found error in expert chess analysis What is the first known example of published expert chess analysis that was disproven by a computer search, with the winning player completely opposite? That is to say, a widely known published analysis by a chess grandmaster of a position with the conclusion that it was winning for one player, but later a computer search proved that actually it was winning for the other player. This comes close, but I am curious to see examples with win-to-lose reversal of opinion. To clarify, I am looking for the first time we discovered that the previously accepted analysis was wrong, and our discovery arose from a computer search.

In the early eighties, the evaluation of the two bishops vs knight endgame was changed thanks to computer-assisted analysis.

Previously, that endgame was thought to be a draw, but now we know the bishops can force a win.

I don't know if this is the earliest instance, but it's definiely a quite old one


Openings that lead to opposite side castling I really enjoy opposite side castling positions where I'm able to launch a kingside/queenside pawn storm and put my opponent under pressure. For this reason, I actually enjoy the Exchange French as Black, and I also want to take up the Scandinavian Defense.
Is there a list of chess openings that commonly lead to opposite side castlings?

Finding out the entire list of common openings is practically impossible. Many players often play by their own strengths, and one opening someone plays might have queenside castling, while others might not, vice versa. That being said, the most common openings and deviations from these are Sicilian, and queens pawn d4 openings. There is no way to accurately predict what a player chooses in a position.
If you enjoy opposite castling, you should wait till your opponent castles, or if you are sure they will not castle in a certain direction then you can also do so.


Why does Lichess mark this move as "?!"? I was looking at this game on Lichess, where it says "Checkmate is now unavoidable. Best move was Kc4." As far as I can tell, checkmate was already unavoidable, including after Kc4. Namely, Black can move Ke3,Ke2,Rf3,Kf1,Kg2,g3 and then either gxh2 or Rxg3 according to White's next move, leading to a won end-game. Am I missing something?

There is no valid human reason. The difference between Kc4 (mate in 12), and Kc2 (mate in 10) is fairly irrelevant. It simply appended the "?!" based on the algorithm that 10 is slightly worse than 12. Either way, it is, indeed, a simple win from there.

By the way, my plan would be Rd7, then bring the king to h1/g1, and only then, bring the rook over via the f-file to take on h2. The longer you can keep the white king out, the less you have to calculate.

In general though, if the situation were different, and the material were more even, you might not want to box your king into the smaller area.

 [FEN "1B6/8/8/8/4k1p1/2Kr3p/7P/8 w - - 0 0"]

 1. Kc2 (1.Kc4)


Full-point-losing move in an endgame rook vs rook? Does anyone know a game, where a full-point-losing move was made in an endgame
 where each side had only one rook and pawns ?

Here's an example between two super grandmasters:

[White "Laurent Fressinet"]
[Black "Vladimir Malakhov"]
[Event "FIDE World Cup 2013"]
[Site "Tromso"]
[Date "2013.08.16"]
[FEN "8/2r5/8/6R1/3k1Pp1/6P1/2K5/8 w - - 4 59"]

1.Kb3 $4 ( 1.Kb2 $1 { The only winning move. } Rb7+ 2.Ka3 Kc4 ( 2...Ra7+ { Continuing to check like this isn't useful, as the king just walks towards the rook. } 3.Kb4 Rb7+ 4.Ka5 Ra7+ 5.Kb6 ) 3.Rxg4 { The win with the connected passed pawns is still a bit tricky, as White's king is badly placed. What follows is a sample line. } Rb5 4.Rg6 Rf5 5.Ka4 Kd4 6.Kb4 Ke4 7.Kc4 Ra5 8.Re6+ Kf3 9.Re5 Ra1 10.Rg5 Ke4 11.Kb5 Rc1 12.Rc5 Rg1 13.Re5+ Kf3 14.Rg5 Ke4 15.Kc6 Rd1 16.Re5+ Kf3 17.Rd5 Rf1 18.Rg5 Rd1 19.f5 Ke4 20.g4 Ke5 21.Rg6 Rd2 22.Re6+ Kf4 23.Rd6 Rf2 24.Rg6 Rd2 25.f6 Ke5 26.g5 Ke6 27.Rg7 Rc2+ 28.Kb7 Rf2 29.Kc8 Rf1 30.Re7+ Kf5 31.Kd8 Ra1 32.Rd7 Kg6 33.f7 Kg7 34.Ke8 Ra8+ 35.Ke7 Rb8 36.g6 Kxg6 37.f8=Q Rxf8 38.Kxf8 ) 1...Rc3+ 2.Kb4 Rxg3 3.Rg8 Ke4 4.Kc4 Rg2 5.Re8+ Kxf4 6.Kd3 Ra2 7.Rf8+ Kg3 8.Ke3 Kg2 0-1

White has a won position here, but must play Kb2.  Instead he played Kb3, which loses to Rc3+. (I have generated a FinalGen tablebase to confirm the status of the positions. The Lomonosov tablebases could be used instead, but I don't have access to them.)


Is analysing moves on separate board in correspondence chess ethical? In Lichess, any form of external help (e.g. engines) is forbidden, even in correspondence chess. However, there is an option to open a separate board where one can make unlimited scratch moves.
I would regard using a separate board as cheating because building
variations in the player's mind is in the spirit of chess and is subject to failures. For example, overlooking a piece that refutes an attack could be eliminated by using a separate board, so while using it will undoubtedly hinder a player's personal improvement, not using it will place him in disadvantage over another player who does.
Assuming external help is forbidden, is it ethical to use a scratch board in correspondence chess? Am I wrong that it goes against the spirit of chess?

Your question is a bit paradox: analyzing is the whole point of correspondence chess (and since strong engines exist, it is sort of a zombie). It is very unfortunate (and not your fault) that Lichess called it that way in the first place: e.g. ICCF explicitely allows engines. Better would be calling it "very long time chess". Consequently, you may analyze per hand. Of course, you again must distinguish from, how shall I call it, postal chess - a friendly game between strangers just for the sake that it's possible (today much faster and easier, of course), and you tacitly agree not to analyze.


In the Giuoco Piano, why is 4.0-0 currently so popular at top level? [FEN ""]

1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.O-O

In recent years, the move 4.O-O has taken over from 4.d3 almost entirely -- in my database of TWIC games, if I look at 2750+ games from the last year, I see 4.0-0 70 times and 4.d3 only 5 times. They mostly seem to transpose into the same positions. This seems to be relatively recent and might be a factor behind the recent popularity of 3.Bc4 (related to the question What happened to the Giuoco Pianissimo? , I turned my comments there into this question).
What's the advantage of 4.O-O over 4.d3?
In case it helps, I seem to recall someone asking this elsewhere (maybe on Reddit?) and a helpful answer linked to some well known commentators explaining it (perhaps Svidler and Gustafsson?). I was at work and didn't watch the video, and I've forgotten where I saw it.

I see two reasons why to prefer castling over c3. First reason why I would go for 4.0-0 is that I would like to postpone playing c3 to make lines with d5 riskier. Imagine Marshall Ruy-Lopez, if the pawn was on c2, white would have very easy life, no weakness on d3, Nc3 possibility. And you can always play the c3 later if you like. The second thing may be desire to avoid playing c3 in early phase at all. White players tried to play a4 to create shelter for the bishop on a2, not minding exchange for opponent's bishop, avoiding classical Bb3-c2 plan.


Why is this the solution to this puzzle? [FEN "2r3k1/5pp1/1q1bpn1p/pB1pN3/P2P4/5R2/1P3PPP/3Q2K1 w - - 0 1"]

1. Rxf6 Qc7 2. Rf3

This is a puzzle (and its solution) I found on lichess.

But I simply do not see the expected logic of this puzzle. The Qc7 move doesn't do much from my POV, and refraining from following up with gxf6 also doesn't make sense as that move wins a rook, and while it does open the king up to check, that check doesn't force any other captures, nor does it lead to mate. In fact, when I analyse the game with an engine, it even prefers gxf6 over Qc7.

There is a lot more to this, and this is really not a great tactics problem as much as it is a continuing the attack problem. The difference is that with a tactic problem, you can see the result all the way to the end. Other positions, you have just a feel for it, and you know that you are probably winning, but you have to play what you can calculate, you get there, and then you calculate more of the attack. Often, you do this while calculating places you could take a forced draw if it is not working out.

A great example of that is the game Dubov-Svane (here with copyrighted annotations), which I will give below. It was one of the best games of the year.

The move Qc7 is an example of why I am not a fan of online puzzles that have been computer checked, but no strong player has evaluated. After Rf6, if you do not take, you simply lose, and thus, Qc7 is not even an option to consider. The only lines that are important are the ones that include gf, but more importantly, the ones that include Bxe5, which comes closer to defending for a human than any other move.

 [FEN "2r3k1/5pp1/1q1bpn1p/pB1pN3/P2P4/5R2/1P3PPP/3Q2K1 w - - 0 1"]

 1. Rxf6 Bxe5 {This may be the most testing try in practice.} (1... gxf6 2. Qg4+ Kh7 (2... Kh8 3. Nxf7+ Kh7 4. g3 {The threat is Qe6.} Bb8 5. Qh4 Kg7 6. Qxh6+ Kxf7 7. Qh7+ Kf8 8. Qh8+ Kf7 9. Qxc8 $18) (2... Kf8 $2 3. Nd7+ Ke7 4. Nxb6 Rc1+ 5. Bf1 $18 {This is obviously important to see.}) 3. Bd3+ f5 4. Bxf5+ exf5 5. Qxf5+ Kh8 6. Qf6+ Kh7 7. Qxf7+ Kh8 8. Ng6#) 2. dxe5 gxf6 3. exf6 Kf8 (3... Kh8 4. Qd2 Kh7 5. Bd3+ Kg8 6. Qxh6 $18) (3... Kh7 4. Qd3+ Kh8 5. Qd2 Kh7 6. Bd3+ Kg8 7. Qxh6 $18) 4. Qd2 Rc6 5. Qxh6+ Ke8 6. g3 d4 {It is clear that that is heading to a queend ending, so maybe d4 would give some counter-chances under slightly more favorable circumstances.} 7. Qh7 d3 8. Qg8+ Kd7 9. Qxf7+ Kc8 10. Qg8+ Kb7 (10... Kc7 11. Qg7+ Kb8 (11... Kd6 12. Qe7+ Ke5 13. Bxc6 Qxc6 14. f7 d2 15. Qg5+ Ke4 16. Qe3+ Kd5 17. Qxd2+ $18) 12. Bxc6 Qxc6 13. f7 $18) 11. Bxc6+ Qxc6 12. Qh7+ Kb6 13. Qxd3 {There are other lines in here, but this line represents a moves that try to fight back until it is finally over totally.}

Here is that fantastic attack my Danil Dubov, which illustrates my point. Dubov most likely did not see everything from move 22 through to move 39, but rather, he saw chunks at a time, and there were probably places he could have bailed out with a draw. This type of attack, while containing tactics, is not one big tactic. I would describe the problem above in the same way, assuming that black played the best practical defense with 1...Bxe5 trying to keep equal material while trading off the key Ne5 attacker.

 [Event "EU-chT 22nd"]
 [Site "Batumi"]
 [Date "2019.10.31"]
 [Round "7.4"]
 [White "Dubov, Daniil"]
 [Black "Svane, Rasmus"]
 [Result "1-0"]
 [ECO "D37"]
 [WhiteElo "2699"]
 [BlackElo "2592"]
 [PlyCount "77"]
 [EventDate "2019.10.24"]
 [EventType "team-swiss"]
 [EventRounds "9"]
 [EventCountry "GEO"]
 [WhiteTeam "Russia"]
 [BlackTeam "Germany"]
 [WhiteTeamCountry "RUS"]
 [BlackTeamCountry "GER"]
 [FEN ""]

 1. c4 e6 2. Nc3 d5 3. d4 Nf6 4. Nf3 Be7 5. Bf4 O-O 6. e3 b6 7. Qc2 Ba6 8. O-O-O dxc4 9. Ng5 Nc6 10. a3 g6 11. h4 Bd6 12. g3 Qe7 13. h5 e5 14. hxg6 hxg6 15. Bg2 exf4 16. Bxc6 fxg3 17. Kb1 Rad8 18. f4 Bc8 19. Rde1 Kg7 20. Nd5 Nxd5 21. Rh7+ Kg8 22. Rxf7 Rxf7 23. Qxg6+ Kf8 24. Qh6+ Rg7 25. Bxd5 Ke8 26. Qh5+ Kd7 27. Qh3+ Ke8 28. Qh5+ Kd7 29. Be6+ Kc6 30. Qf3+ Kb5 31. Bxc4+ Ka5 32. Qd5+ Bc5 33. b4+ Ka4 34. Qg2 Bxb4 35. Qc6+ Kxa3 36. Bb3 Bd7 37. Qc1+ Kxb3 38. Qc2+ Ka3 39. Qa2# 1-0

P.S. The only "logic" to it is that someone, who was not that strong fed it to a computer, and posted only the computer's best moves, but not the ones that would challenge a human the most.


What are the rules of Quantum Chess? The game Quantum Chess, as seen in the video where Paul Rudd defeats Hawking, has no "set of rules" written down. You either have to do the in-game tutorial, watch a video on the game and pick them up.

So what are the rules of Quantum Chess?

This refers to the game (currently only available on steam) created by Chris Cantwell.

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 is in that square.

Modifications to existing chess rules

A player is not required to move their king out of check and the game concludes when there is a 100% probability that one of the kings has been taken. As a result there is no checkmate.
All promotions result in a queen as of 10/8/17, since underpromoting has not been implemented into the game.

Movement

All pieces move as usual in normal circumstances.
On any given turn, the player can make one quantum move instead of a normal move.

Quantum moves

Quantum moves are notated with the ^ symbol. (e.g: N^d4)
When quantum moving a piece, it can make up to two normal moves.
The probability of the piece moving is equal to the probability that the piece has not moved, resulting in a superposition of multiple board states.
A quantum move cannot be used to take a piece.
Pawns cannot make quantum moves.

Superposition

When any quantum move is made, that piece exists in multiple places simultaneously. This is represented by multiple copies of the piece displayed, with appropriate meters to show the probability of finding the piece in that square. There is only one piece, but it can exist in one of multiple places.
If a piece "takes" one of the copies of another piece in superposition and has  100% probability of being available to take it, the piece is taken if it was in that square. Since there is a probability of the piece being in other squares, those copies of the piece remain, however there is now a chance that the piece has already been taken and is no longer on the board.

If a piece "takes" one of the copies of another piece in superposition and it is not certain that the piece was available to take it, a measurement occurs. A measured piece will collapse onto one square using a random selection. The probability of it collapsing onto a particular square is the same as the probability that is was moved there. All pieces that are entangled with the measured piece will also be measured and may have their outcome influenced by the measurement of the piece(s) that they are entangled with.

A pawn can be put into superposition if it takes a piece which is in superposition. If the piece was there, the pawn could take it. If not, moving diagonally was an illegal move. The probability of the pawn being on the new square is the same as the probability that a piece was there to be taken.

A pawn can also be superimposed by moving two spaces forward, through a square which may contain a piece. This results in entanglement.

Entanglement

Entanglement occurs when a piece attempts to move through an instance of a piece in superposition. The probability of the moved piece existing in its new square is the same as the probability that the obstruction was not there to block it.
If a piece is entangled with another piece and is measured, both pieces are affected by the results of the measurement accordingly.

Special circumstances

The following "rules" are combinations of rules from above, however they are worth mentioning as useful tactics:

Quantum Trading

It is possible to trade probabilities of pieces, leading to complex trading. For example, it is possible to trade knights in a way which leaves one player with a 2/3 chance of having a knight, and the other with a 1/3 chance of having a knight. The first player is more likely to have benefited from this trade, however it is uncertain until measured.

Schrödinger's King

If the king is in superposition and one of the instances is taken, the probability that that player has lost is equal to the probability that the king was in that square. Since it is not certain that they have lost, play continues.
This means that it is possible for a player to win a game with a probability that they have already lost by fully capturing the opposing king.

Ghost capture

This is a result of a pawn taking a piece in superposition. If there is one other state of the taken piece still on the board and a piece attacking it, ghost capture can take place. If the attacking piece must move through the square where the pawn would be if it hadn't moved in order to attack the superimposed piece, two outcomes can occur:

The measurement confirms that the piece had not moved, so an attack is impossible and the opposing player gains "half a piece".
The measurement shows that the piece has moved and has already been taken, so the opposing player loses "half a piece".

Quantum Castling

If there is a probability that a piece is between the king and rook, the probability of castling is equal to the probability that the piece was not there. A measurement may take place if two pieces end up on the same square.
If there is a probability that the rook may have moved, castling can occur with the probability that the rook is available to castle. The king and rook are now entangled since the castling move depends on whether the rook was on the correct square.

Double Castling

After a quantum castle, the king can castle the other way if the rook is available, with the probability of castling being the probability that the king is there.

In this example, both sides have castled both ways:


What would be the ELO of modern-day centaurs? The last public ranking of chess centaurs was in 2014, and only compares centaurs to each other. As of 2018, what would be the ELO rating of the best centaurs compared to the best humans and chess engines?

This is similar to this question, but two differences:

It is specifically about if centaurs beat computers, which is a subset of this question
The top answer is about a GM with a computer who does not have any training as a centaur, while we know that good centaurs have very different skills than good humans do.

Chess centaurs is not correspondence chess because centaur matches are played under the classical time controls. Unfortunately, centaurs is dead because the best strategy is just follow the engine moves.

In classical time controls, there's generally no advantage for human assistance. Humans are too slow, too clumsy etc ... we need more time.

This is 2018, centaurs matches are absolutely meaningless. They are like computer matches with dumb human intervention. Computer engines play stronger than human+computer unless the human player has sufficient time to digest the positions.

The answer to your question is the same ELO as the engine itself.


How to proceed after declined Queen's Gambit? I am a intermediate-level player. How can I proceed after a declined Queen's Gambit, as White?

There are multiple options here. I'm not sure what you mean by "an intermediate player", so the amount of specific lines you'd like to study can differ. I'll focus instead on types of pawn structures and middlegames you can reach. Let's take the reference position 1.d4 d5 2.c4 e6, even though there are different move orders available:
Black will sometimes play an eventual ...c5. This can lead to two types of pawn structures: the Semi-Tarrasch type, where you get pawns on e4 and d4 (see for instance 3.Nc3 Nf6 4.Nf3 c5 5.cxd5 Nxd5 6.e4). This often leads to a comfortable position for White due to his superiority in the center and not enough counterplay chances for Black to compensate for it. Here you have an example from top level players.. This line has some similarities with the Grünfeld Defence (see 1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.cxd5 Nxd5 5.e4 Nxc3 6.bxc3), but I'd say Black has more chances in the Grünfeld. In my opinion you should try to reach this pawn structure as often as possible.
Another typical pawn structure that is often reached is one with an isolated "d" pawn. You'll probably play both with and against that isolated pawn in several occasions, you that's also something you may want to get familiar with. chess.com has an article about it that you may want to check out Note that this structure can also be reached when the Queen's Gambit is accepted.
Then there's the "minority attack" type of game. This happens when you capture on d5 and your opponent retakes with his "e" pawn but ...c6 has been played instead of ...c5. Here you can play on the queenside trying to get your semi-open "c" file fully open. I'm not really well-versed here so I'll let someone else choose an illustrative example by editting this answer.
Finally, there are some lines where Black will enter some variation of the Slav Defence (with ...c6). I don't know how well you know the lines after 1.d4 d5 2.c4 c6 and your preferred move choice can chance according to that. For instance, you can try 3.Nf3 Nf6 4.e3 so now you can answer to 4...c6 with 5.Nbd2!? if that's the particular line you enjoy against the Slav (here your plan would be to make a quick e4 push). But if you're not interested in playing that then you may prefer 3.Nc3. There are several lines you can choose from and plenty of transpositions between them.


Theoretically, shouldn't analysis of any chess move have exactly nine possibilities? Since chess is finite and deterministic, it is theoretically possible to objectively label any position as winning, losing, or drawn. For example, it seems very likely that the starting position is drawn.

Therefore, the current system of "score" that engines use to analyze a position is actually nonsense from an objective point of view. With enough depth, the "score" would always be +100 (or whatever the engine uses for forced checkmate for white), 0 (drawn), or -100 (forced checkmate for black). Are these not the only possible evaluations of a position?

If so, it follows that moves can be characterized in exactly 9 ways. If W, L, D represent won, lost, and drawn positions, the nine possibilities can simply be written as ordered pairs of game states before and after the move.

For example, a move that makes a won position into a drawn won could be (W,D).

Our intuition of a range of severity for mistakes is something that a theoretical supercomputer would not share. Is it then meaningless to speak of how bad a mistake is? It seems to me that the only relevant point is whether it changes if the game is objectively won/lost/drawn.

You are somewhat correct. In theory, each position can be correctly categorized in one of three ways -- win for the side to move, loss for the side to move, draw, all presuming "best play" by both sides from that position. That last caveat is required to make the ideas of "will win", "will lose", and "will draw" well-defined. But that caveat also means that the side to move can never improve on the position categorization, because that categorization already presumes (prices-in) that the side to move will make its best move. So the only possibilities for move categorizations are: (W,W), (W,D), (W,L), (D,D), (D,L), (L,L). I.e. six instead of nine. The side to move can only hold or worsen (blunder) its theoretical value, in other words.

As for severity of error, presumably (W,L) is worse than (W,D), but other than that, blunder is blunder, yes ((W,D), (D,L)). And any move that maintains value is a theoretical non-blunder, yes ((W,W), (D,D), (L,L)).

As to engine scores, they are in most cases theoretically "meaningless" I suppose, as above, but not objectively so. They could be considered to be trying to estimate the probability that the theoretical value is closer to W, D, or L, on some scale, given the data they have been able to glean so far in their forward position search. And sometimes they do produce theoretical values (forced-mate detections). But I've also got to think that the error-bars on non-theoretical engine values are also pretty large, meaning that we're talking about estimates of estimates of probabilities, which is pretty, well, non-definitive...

Also, see Saibot's answer regarding so-called Tablebases. Chess has been solved theoretically for all positions with 7 or fewer pieces on the board (two kings plus up to any five pieces). Here is an online resource for most of the 6-piece tablebases: http://www.k4it.de/?topic=egtb&lang=en

Another wrinkle on theoretical categorizations is "distance to mate" for W and L positions. Presumably a win in fewer moves is theoretically "better", so a (W,W) move that doesn't reduce "distance to mate" could be considered a "blunder" as well, as could a (L,L) move that shortens "distance to mate".


Calculation skills to 2000 and beyond I'm rated about 1900 USCF and have been stuck between 1800-1900 for a few years not really knowing how to break through to 2000+. I have a good amount of positional understanding and solid foundation in tactics, i.e. I've gotten quite good at solving tactics problems.

That being said, I lose a lot of games due to poor evaluation, time pressure, and erratic blunders. I think that essentially everything in chess goes back to the skill of calculation, including things like time pressure, which is due to inefficient calculation.

So then, how do I further improve my calculation? More visualization exercises? Playing blitz until I can't see straight? Mental exercises? I feel like my visualization is already decent, as I can successfully play 3 blindfolded games at the same time (that's the most I've tried at least). I just don't understand what I've been missing out on that improves my calculation. And if it matters, I'm 20 years old.

Thanks!

If you can play three games blind-folded, it is unlikely that your problem is calculation. I dare say that there aren't many 1900 USCF players that can do that.

You say you "lose a lot of games due to poor evaluation, time pressure, and erratic blunders". That also doesn't cry out "calculation problems" to me.

In my experience ratings first and foremost reflect positional understanding. Calculation skills make a much smaller difference, at least above a certain threshold.

To be clear, positional understanding isn't knowledge as much as a good feeling for the position. I.e. whether you can precisely estimate how good your position really is and quickly come up with sensible moves and plans.
If you are lacking in that department you tend to calculate a lot without achieving much. That results in time pressure and blunders just as surely as having calculation deficits.

So I would rather recommend a book like Positional Play by Jacob Aagaard. If you can easily solve the problems in this book, you can always go back to pure calculation.

By the way, there is a big difference between training calculation and training tactics. Solving tactics depends on seeing motives, training calculation depends on the ability to think far ahead without confusing yourself. So if you do go back to pure calculation, maybe you should try the Calculation book by Aagaard, or similar books by Dvoretsky.


Is it disrespectful to pay attention to other things while playing? Sometimes when I'm playing a variation that I'm comfortable with I get bored while waiting for my opponent to move, so I get distracted and start to pay attention to other things around me.

I know that focus is important, and being distracted can put me on short pants when playing, but lets, for the purpose of this question, ignore that.

As an example, yesterday I was playing with my uncle with no time limit, and the Real Madrid game was on. While waiting his moves I took a (sometimes not so) quick look at the TV.

Obviously, my uncle is someone I respect. When doing this I had (and always have) no intention of looking presumptuous or insinuate the game is easy (and I don't think my uncle got me wrong).

But not everyone I play against knows me as well as my uncle. Does this look bad when playing? Can my opponent be offended?

Whether or not your opponent is offended may depend on your local culture outside of chess, and might also depend on the situation in which you're playing the game. In a tournament with slower time controls, it's not uncommon to even see players get up and walk over to watch other games in progress. On the other hand, if you're just playing a casual game with someone then it's probably polite to pretend you're interested in the current position because otherwise your opponent may think that you don't actually want to be playing with them.


Good books for- Grunfeild and Sicilian defence Can you please recommend good books for- Grunfeld and Sicilian defense. Would prefer separate books for either. Specially one which contains deeper analysis and has recent games illustrated.

There are many types of Sicilians so you should specify which one you intend to play,

But generally a good book is: Starting out: The Sicilian by John Emms

Although there are a whole multitude of excellent books written about specific Sicilians so if you could specify more than I could recommend some excellent books on those specific Sicilians.

For Grunfeld it's a little simpler, an excellent book is Understanding the Grunfeld by Jonathan Rowson, which is a very well regarded book.

There are many more excellent Grunfeld books but far too many to mention in this post.


A castling variant-how would it change the game? In chess, castling can't be done if the king or relevant rook have moved. How would the basic strategy of the game change if the king and rook could castle after moving? Also, how would the game change if the queen castle as well?

In most cases, I'd imagine the queen wouldn't castle, as it would mean it would have a harder time getting out. The only useful case I can think of would be if you developed your bishop to e3 and "castled" queenside with your queen, putting it on c1, preparing for Bh6 to potentially trade off a fianchettoed bishop while also bringing your a1 rook to an active square.  Being able to castle with your king or rook after you moved would change chess quite substantially, and it'd be difficult to quantify all the changes, but if I had to guess, kings would stay in the center longer and rooks would move around more in the middlegame.


How to start learning theory? (1850 Elo) I have been playing online chess (lichess.org) for three years at the rate of a few hours a week and I recently reached the score of 1850 Elo points in bullet mode.

So I want to take more seriously chess and in particular to learn the theory.
To tell you the truth, I've never done any tactical exercises, I don't know any openings or complex finals.

How do I go about it? I am not at all afraid to use books.

Learning theory involves some memorization of moves, but it's also important to understand the core ideas behind the moves. With these ideas, you can figure out what to play in novel situations not covered by the theory you've studied (or if you end up in a position that you forget).

There are different ways to study using an opening book. If you have a program like Chessbase, you could input the moves given, and also annotate in what you think the main ideas are. A good chess book will also take the time to explicitly explain the main ideas; some don't, which will require you to think on your own why a move was given. If you don't have Chessbase, I suppose you could go through the moves on an actual board, and jot down your notes somewhere (like in Word or a notepad).

If you're trying to get better at a new opening though, I'd suggest playing something longer than bullet - try at least 5 0. You want time to think about the position and apply the ideas (and moves) you've learned.


chess program wilhelm I still search an executable file of the chess program wilhelm. It is not only a chess
 endgame database, you can fix pieces to be on concrete squares and check all such position
 to get a statistic how many positions are won/draw/lost.

I downloaded a version long ago, but it did not work. I could not find any results.

Does anyone know if there is an executable file ? And if yes, does it also consider
 DTC or DTZ - metrics ?

Here is a link with informations you can get on chess program Wilhelm.

http://web.archive.org/web/20081208015339/http://www.geocities.com/rba_schach2000/overview_english.htm

Unfortunately, this chess program by Rafael B. Andrist stopped being developped in 2006.


Willingly giving up castling rights in the opening? [fen ""]

1. d4 Nf6 2. c4 d6 3. Nc3 e5

I've seen the Ukrainian/Old Indian Defence played in several GM games before 1970, and was wondering what black gained from willingly giving up castling rights in the opening. According to this source, black actually scores better in the variations where white deprives black of castling rights by trading queens, such as by 4. dxe5 dxe5 5. Qxd8+ Kxd8. So where exactly is black's compensation for the loss of castling rights? I've heard that one can get away without castling if queens are off the board; but this is still the opening and the position looks fairly open (even centre control of both sides is more or less the same), so it seems to me that white can purposefully develop its pieces towards the now exposed black king, while black might have to spend several moves to get its king to safety.

Weaknesses like doubled/tripled pawn structure, color complex holes, and right to castle only matter in chess to the extent to which the opponent can exploit them. In the Old Indian variation you gave above, yes, Black lost the right to castle, but is White in any real position to exploit it? The answer is no. In fact, Black's king is very safe after he plays c6 because he can then tuck his king into c7 and there isn't any real way for White to even check him. The pawn and c6 prevents Nd5 and Nb5 checks, and Bf4 check isn't gonna work because Black will probably post his bishop to d6 and/or play e5, so his king is clearly not "weak" despite the loss of castling rights.

There is another position in the Sicilian Four knights that goes something like:

[fen ""]
1. e4 c5
2. Nf3 Nc6
3. d4 cxd4
4. Nxd4 Nf6
5. Nc3 e6
6. Nxc6 bxc6
7. e5 Nd5
8. Ne4 Qc7
9. f4 Qb6
10. c4 Bb4+
11. Ke2

While Ke2 aesthetically looks ugly because it loses castling rights and also blocks the light-squared bishop from developing, the point is that after Ke2 - f3, the king is extremely safe. If you look at that position yourself, I challenge you to even come up with a plan for Black to check the white king. If you can't, that's okay, because White's king is quite safe on f3.

Here is a counter example. This is from a game I played recently actually where I'm black.

[fen ""]
1. e4 e5
2. Nf3 Nc6
3. Bc4 Nf6
4. d3 Be7
5. Nc3 O-O
6. Be3 d6
7. h3 Na5
8. Bb3 Nxb3
9. axb3 d5
10. exd5 Nxd5
11. Nxe5 Nxe3
12. fxe3 Bh4+
13. Kf1

Here, Black has sacrificed a pawn to force White to lose castling rights with the annoying Bh4+. Notice though that there are a number of factors in this position that makes losing castling rights much more serious in this position than in the previous position. First, Black has the bishop pair which alone is good compensation for the pawn. Second, White has all these dark square weaknesses on g3, h2, and f2, and Black has the dark-squared bishop. White also lacks his own dark-square bishop to protect those squares, so it only heightens the problems of losing his dark-squared bishop. Third, White's king position here impedes the development of his h1 rook, so his pieces are more awkwardly placed.

You can argue Black has lost a pawn, but I would argue that the pawn sac has forced White to lose a rook, because it will be very difficult to get his h1 rook into action. All these factors make losing castling rights here really really bad for White because Black has these compensating factors that allow him to take advantage of White's compromised king position and loss of castling rights.

So the takeaway from this is that with any weakness—be it losing castling rights, or pawn structure weaknesses—a weakness is only a weakness if it can be exploited by the opponent. In all mainline openings where one side loses the right to castle, or takes on any other sort of weakness, it is because that side willingly loses the right to castle because his king position can't be exploited and because other aspects of the position trump king safety/castling rights.


What would chess openings be like without castling and/or the double pawn move? Chess has a fairly elegant set of rules, but it has two rather ugly "rules hacks" in it:

Pawns can move two squares forward, but only on their first move, and have the rather ugly rule of en passant to get rid of the nasty side effect of having your 5th rank pawns get bypassed.
Castling lets you move two pieces at once, and has a bunch of rules about when you're allowed to do it.

Now, the usual justification of these is that they make the game go faster. According to this question, the two-square pawn move was introduced because players would begin each game with 1. e3 e6 2. e4 e5 (or similar). Castling was a variation on the "king's leap" many chess variants had. It makes a certain degree of sense--games are meant to be fun, and why not get to the action more quickly?

On the other hand, chess theory has advanced a lot since the 1500s. In modern opening theory, black often forgoes immediate center pawn moves. 1. e3 would likely meet the reply 1... Nf6, not 1... e6. It stands to reason that some of the considerations then may no longer be the case.

So, has anyone ever done any studies into what chess openings would look like without castling, without the double pawn move, or both?

Overall, the game would be slower and opening attacks would be more aggressive at times.
The purpose of implementing the double-step was to speed up the game. That way, those pesky pawns wouldn't have to waste so much time, i.e. moves, moving forward to mount an attack or to develop an area of advantage/control. But with the double-step gone, we would have to revert back to the slow way of the ancients.
The double-step is often done on the c and f files to let the knights out without blocking the pawns. Now it would take more time to flesh out that plan, as it would now take two turns to let the knight out onto its most advantageous opening square.
In some semi-closed positions, the double-step is used as an immediate can opener. However, having to move the can-opener pawn two times might give the opponent just enough time to react and defeat, or at least nullify, your attack. A few more draws might result because the position stays closed.
Additionally, in some games, the double-step is used to quickly advance a rook pawn, and break open the enemy's king's encampment. But with it gone, a single step must be done, thereby giving the opponent time to react. Have a look at the below position and deduce for yourself how this affects the game.
 [FEN "3r1r2/1bp3k1/1p1qp2p/p2p2n1/5NQ1/PBNP2P1/1PP4P/1K2R2R w KQkq - 0 1"]

As for no castling, it would also lead to a slower game, but at the same time lead to more aggressive opening attacks. The concept of castling, even if the move isn't allowed anymore, would still be a popular motif due to how it keeps the king safe.
Doing castling manually takes several moves, and with both players doing so, games would start to be several moves longer. Due to the slow process of doing so, an opponent may try to catch the king in the act and take him down. Kings would be in the center longer, also leading to a reason to favor, and as such an increase, in open positions. That allows for an attack to be done faster. Artificial kingside castling would increase in use due to the process taking much longer than on the queenside.
At the same time, however, with the hindrance of the double-step, such attacks may be also seen less often due to the need to spend time mobilizing pawns. The enemy might use your time to manually castle, ruining your plan.


Beautiful retrograde analysis problem by Alexsey A. Troitsky I saw this beautiful, subtle & accessible problem a couple of days ago, and wanted to share it with you folks. (It's by the ground-breaking endgame theorist who e.g. invented the "Troitsky line" in KNNvKP analysis.)

[title "A.A.Troitsky - Bohemia 1910"]
[fen "1B6/bp3ppp/BR1pPp2/RPp1kP2/bpK5/3P2P1/1PP3PN/5nrr w - - 0 1"]

White to play and mate in 2?

The forward play is pretty obvious. But, as is common in retrograde analysis, you need to justify the forward play by figuring out what was Black's last move.

Even if/when a speedybrain supplies a full answer, I hope that you can still enjoy solving the puzzle.

Short answer: last move was -1. c7-c5, and before that -1...Rc6-b6, the white bishop returns to c1 and -d2-d3 unlocks the cage, enabling -Kd3-c4 and everything unlocks. -1. c6-c5 doesn't work because the white bishop will definitely end up trapped behind the black bishop in the northern dark squares and can't get out - -c6-c7 will leave the two bishops on d8/e7/f8 and not a7/b8 because of tempo concerns (retro-opposition), and they can't leave.

(Notice the use of minus signs, white moves noted with ..., and I said the white bishop "returns" to c1 - I'm retracting moves from the diagram position, which makes this kind of problem much easier.)

Long answer: Now how to explain this without fluff or skipping too many "obvious" details? From a pedagogical point of view, I will insist on talking about this problem using retractions rather than the usual forward chess moves; it's easier and far clearer to play moves backwards from the diagram than it is to create some arbitrary position, assert that it's legal then play forward moves to reach the diagram. It also ensures we don't miss anything - easier to check every possible retraction from the diagram than to check that every possible chess position leading to the diagram has ends with a certain move.

Those who already understand retraction can probably see the cage themselves, skip the first two bolded points and jump right to the section -1. c7-c5.

Pawn captures, basics of retraction explained

Standard approach is to look at pawn structure. Each side has 14 units and 8 pawns. White's captures were hxg3 and axb, black's were exf6 and axb. So from the diagram, we can't magically retract (take back) an uncapture immediately.

Also, the fact that all bishops are on the board and each side has their full 8 pawns means we can't retract exf6, d7-d6 or ...d2-d3 without the corresponding bishop being at home. (In the forward direction, it means that the pawn move was played while the bishop was at home and hadn't yet moved.)

A side can retract themselves into check but the other side must retract immediately to remove the check (once again this is seen in reverse - in the forward direction, one side checks and the king moves away.) For instance -1. c6-c5 Kb3-c4 would be possible, except that black can't remove the check from Ba4. -1. Kf4-e5 is impossible as white needs to retract -1...hxg3 to answer (pawn structure.) -1. Ne3 is impossible as one cannot deliver check by retracting (in the forward direction, that would be black moving away from check.)

What is a retrocage?

Usually, once all pieces have enough freedom of retraction, the position shouldn't pose any legality problems. We therefore want to retract moves with the goal of freeing as many pieces as possible. By considering all retractions (it's not hard once you're used to it, like seeing legal chess moves), we notice a few things:

The kings can't retract at the moment.
The southeast (bottom-right) corner unlocks with retracting a knight move, impossible for now because of the kings.
The west (left) side, specifically the 8 pieces in a rectangle except bBa7 and wRb6, is a cage that unlocks only with -Bb3-a4, which is again impossible because of the kings.

So to unlock the position, we need to free the kings by giving them a retraction. So a bishop has to go home to c8, f8 or c1 to enable a pawn retraction to (respectively) d7, e7 or d2. The black light bishop is trapped on a4, so that leaves just the two dark bishops.

Position is legal: -1. c7-c5

We retract for example -1. c7-c5 Rc6-b6 -2. Be3-a7 Bb8-a7 -3. Bh6-e3 Be3-a7 -4. Bg5-h6 Bc1-e3 -5. Bh6-g5 d2-d3 (the white dark bishop came home) -6. Bg5-h6 Kd3-c4 and the cage unlocks. The white king moving frees everything, as explained above.

En passant is legal: -1. c6-c5? is impossible

The crux of the matter. If we try to retract this, then the two dark bishops are locked in step on the 6 dark squares in the north. They can't pass each other, nor can they lose a tempo since there are no other legal retractions except -c7-c6, which incidentally commits the bishops to the dark squares to the left or right of c7. There are only 3 cases:

Both bishops on the left (bBa7/wBb8). This is impossible - the bishops can't lose tempo, and with the bishops in such a position (i.e. right now, the only chance) it's white to retract, not black.
Both bishops on the right (bBd8/wBf8). Once -c7-c6 is retracted, the bishops are trapped in these squares. The only way to let them out is to retract e7xf6 (impossible; the black bishop can't find itself on the right of the white one to be at home on f8), or to retract -d7-d6 (also impossible; the black light bishop on a4 can't come home before the cage is unlocked.)
Black bishop on the left, white bishop on the right. The same problem as in (2), we can't get either bishop home as they're each trapped on the wrong side of the pawn wall.

With no other way to unlock the position, we conclude that -1. c6-c5 is impossible.

Conclusion:
Therefore -1. c7-c5 was the last move (no other possibilities), so en passant is provably legal and forward mate is 1. bxc6 e.p.+ Bb5 2. Raxb5#.


Tools specifically for training at finding loose pieces? There are of course lots of tactical trainers out there, but I'm wonder if there are any that focus solely on the basic skill of spotting loose or hanging pieces. It is of course a trivial exercise when given enough time: one could just look at each piece in turn and see if it's being attacked/defended. Under time pressure, it's a different story: I often lose under time trouble not even due to a tactic but due to leaving a piece simply hanging.

I'm amazed that when I show a position to an expert, within a fraction of a second they have already spotted all the loose and hanging pieces, whereas I might take at least several seconds to do the same, and sometimes even miss some!

What I'm envisioning is something that shows a position and says "click on all the loose pieces" and the goal is to solve as many of these as possible within a certain amount of time. In other words, something like the Lichess coordinate training tool (https://lichess.org/training/coordinate) but for loose pieces instead of coordinates.

I don't know of any such tool. A paid membership at ChessTempo might allow you to filter problems for the hanging piece motif. Not exactly the type of tool you imagine, but something comparable.

However I would argue against the usefulness of a tool that you describe for the following reason.

If I play chess (and I presume most other players beyond beginner level as well), I do not scan the board after every move for attacked pieces, which is what you are trying to train.

Instead I ask myself: "What did the last move change with regard to attacked pieces? There are only a few things that change if you move a piece:

the piece will attack new squares from its new position
the piece will stop attacking some squares that it used to attack on its old position
moving the piece can open lines/diagonals for other pieces to attack something
moving the piece can block lines/diagonals for other pieces

Of course, a move can also interrupt you from defending a piece or can create all kinds of multi-move tactics. You don't need to learn a new way of thinking to include these, as you advance in chess: just rephrase/generalize the question to: "What did the last move change with regard to the position?" Anyway, for the time being let's stick with attacked pieces which is what your question is about.

If you look a bit more careful you will soon recognize some features of chess pieces which make answering the question easier. For instance if you move a rook horizontally, it will still attack squares along the line that you moved it, however all the squares that it attacked vertically change. Similarly for the bishop: if you move it along one diagonal, it will essentially only change things along the other (perpendicular) diagonals.

Also, you can take into account the range of pieces to quickly assess whether something is getting attacked. For instance pawns are very short range and it is very easy to see whether they attack anything. Similarly if your opponent does some moving around far away from any action, behind his pawn chain (e.g. castling), chances are that this does not attack anything new.

So my recommendation would be to go with an incremental approach, storing the attacked pieces (later you will add all possible tactics/strategies) in your memory and update your memory after every move.


Why pin knights early in the opening? I am a beginner amateur player, and I have been thinking about openings. On lots of occasions the opponent pins the white knight on Nc3 or Nf3 (as black) or the black knight on Nc6/Nf6. What is the main motivation for doing that? I am partial to bishops, and it seems even opening theory suggests that it is okay to get rid of one or even two bishops early in the opening at the cost of your opponents pawn structure? It seems very counter-intuitive to me. Can someone give examples of games/tactics where the pinned knight gives a big advantage for the opponent?

One of the key principles of opening play is that control of the center is vitally important. If one of the players has complete control of the center then they can much more easily launch an attack and it is much more difficult for the other player to defend.

A white knight on c3 supports/attacks e4 and d5.
A white knight on f3 supports/attacks e5 and d4.

Those 4 squares define the center of the board. A similar story is true for black knights on f6 (controls e4 and d5) and c6 (controls e4 and d5).

A pinned knight doesn't support or attack any squares. It is pinned. It can't move. It no longer plays any role in the fight for the center although it can come to life again if it is unpinned.

Hence the normal progression in the opening of moving a center pawn 2 squares to control one of the center squares, then move one or more knights out to also control center squares, then move bishops out to either control center squares or to pin opposition knights which has the same effect.


Why is 6. a3 a mistake compared to Qa4+? I played a game on lichess recently. Afterwards, I used the analysis feature, including the "learn from your mistakes" feature, and it said that 6. a3 by white was a mistake, with 6. Qa4+ as best. I'd like to know why, as I don't understand why 6. Qa4+ is superior.

[After Qa4+ , it seems to me black can play 6. Nc6, and if the white queen captures the black knight, 7. Qxc6, it seems to lead to a draw as the white queen cannot escape capture threats starting with 7. Bd7 by black.]

   [FEN ""]

   1. d4 d5 2. e3 { D00 Queen's Pawn Game } a6 3. c4 b6?! { (0.12 ? 1.07) Inaccuracy. Best move was e6. } (3... e6 4. Nf3 c5 5. cxd5 exd5 6. Nc3 Nf6 7. Bd3 c4 8. Bc2) 4. Nc3?! { (1.07 ? 0.50) Inaccuracy. Best move was cxd5. } (4. cxd5 Nf6 5. Nf3 Bb7 6. Be2 Qxd5 7. Nc3 Qd6 8. O-O Nbd7 9. Nd2 e5 10. Bf3 c6) 4... e6 5. Nf3 Bb4? { (0.17 ? 1.63) Mistake. Best move was Bb7. } (5... Bb7 6. b3 Nf6 7. Bb2 Bd6 8. Bd3 O-O 9. O-O Nbd7 10. h3 c5 11. cxd5 exd5 12. Ne2) 6. a3? { (1.63 ? 0.59) Mistake. Best move was Qa4+. } (6. Qa4+ Nc6) 6... Bxc3+ 7. bxc3 f6?! { (0.65 ? 1.60) Inaccuracy. Best move was Nf6. } (7... Nf6 8. cxd5 exd5 9. Be2 Nbd7 10. O-O O-O 11. a4 c5 12. c4 Bb7 13. Bb2 Rc8 14. Nd2) 8. Qc2 g6 9. cxd5 exd5 10. c4 Ne7?! { (1.74 ? 2.43) Inaccuracy. Best move was Bf5. } (10... Bf5 11. Bd3) 11. cxd5 Qxd5 12. e4?! { (2.47 ? 1.93) Inaccuracy. Best move was Bc4. } (12. Bc4 Qd6 13. O-O Be6 14. d5 Bf7 15. Rd1 b5 16. Ba2 Nd7 17. e4 O-O 18. Be3 g5) 12... Qd6 13. Be2 Bg4? { (2.31 ? 3.33) Mistake. Best move was Bb7. } (13... Bb7) 14. Bb2?! { (3.33 ? 2.57) Inaccuracy. Best move was O-O. } (14. O-O Nd7 15. Rd1 h5 16. h3 Bxf3 17. Bxf3 Kf7 18. a4 Qc6 19. Qd3 Qe6 20. Bf4 c6) 14... Nbc6?! { (2.57 ? 3.07) Inaccuracy. Best move was Nd7. } (14... Nd7 15. O-O O-O 16. Rfd1 c6 17. a4 Rfe8 18. Ba3 Qb8 19. Qb3+ Kh8 20. Bc4 Kg7 21. Bf7) 15. d5? { (3.07 ? 1.98) Mistake. Best move was O-O. } (15. O-O) 15... Bxf3 16. Bxf3 Ne5 17. Be2 b5 18. O-O O-O 19. Bd4 Rac8?! { (2.29 ? 3.12) Inaccuracy. Best move was f5. } (19... f5 20. Bc5 Qd7 21. Rfd1 Nf7 22. exf5 gxf5 23. d6 cxd6 24. Qb3 d5 25. Qg3+ Ng6 26. Bxf8) 20. f4? { (3.12 ? 1.35) Mistake. Best move was Bc5. } (20. Bc5 Qd7) 20... Nc4? { (1.35 ? 3.56) Mistake. Best move was Nd7. } (20... Nd7) 21. Bxc4 bxc4 22. Qxc4 c5 23. Be3 Kg7? { (3.59 ? 4.87) Mistake. Best move was f5. } (23... f5 24. Rac1 fxe4 25. Bxc5 Qxd5 26. Qxd5+ Nxd5 27. Bxf8 Rxf8 28. g3 Nf6 29. Rc6 a5 30. Ra6) 24. Rac1 f5? { (4.67 ? 6.59) Mistake. Best move was Qd7. } (24... Qd7 25. Bxc5 a5 26. Qc3 a4 27. Qd4 Rfd8 28. Rc4 Qe8 29. Rfc1 Qf7 30. Rxa4 Nxd5 31. exd5) 25. Bxc5 Rxc5?! { (5.89 ? 6.59) Inaccuracy. Best move was Qd7. } (25... Qd7 26. Qc3+) 26. Qxc5 Qxc5+ 27. Rxc5 fxe4 28. d6 Nf5 29. d7 Rd8 30. Rd1 e3 31. Kf1 Ne7?! { (6.49 ? 7.39) Inaccuracy. Best move was Kf8. } (31... Kf8 32. Ke2 Nh6 33. Ra5 Ke7 34. Rxa6 Ng4 35. a4 Nf2 36. Rd4 Ng4 37. h3 Nf6 38. Kxe3) 32. Ke2 Nf5? { (7.22 ? Mate in 10) Checkmate is now unavoidable. Best move was Kf7. } (32... Kf7 33. g4 a5 34. a4 h5 35. gxh5 gxh5 36. Rxa5 Ng6 37. Kxe3 h4 38. Rad5 Ke7 39. a5) 33. Rc8 Rxd7?! { (24.96 ? Mate in 8) Checkmate is now unavoidable. Best move was Kh6. } (33... Kh6) 34. Rxd7+ Kf6 35. Rc6+ Nd6 36. Rcxd6+?! { (Mate in 2 ? Mate in 2) Not the best checkmate sequence. Best move was g4. } (36. g4 a5 37. Rcxd6#) 36... Kf5 37. Kxe3?! { (Mate in 2 ? Mate in 4) Not the best checkmate sequence. Best move was Kf3. } (37. Kf3 g5 38. Rf7#) 37... Kg4 38. Rxh7 g5 39. fxg5?! { (Mate in 3 ? Mate in 4) Not the best checkmate sequence. Best move was Ke4. } (39. Ke4 a5 40. Rg6 a4 41. Rxg5#) 39... Kxg5 40. Rc7 Kf5 41. Rc5+ Kg4 42. Rd4# { White wins by checkmate. } 1-0 *

In short: Qa4 forces black to lose grip over central light squares as black is tactically being restricted to recapturing with a queen on d5 instead of a pawn, leading to:

As opposed to any of the actually desirable and common setups for black, which might look like: (with Nf6 instead of Bb4, and quick Bb7 and castling being prioritized)

It helps to try and understand the purpose of every move at a basic level, let's start with your 3rd move c4: Clearly, one of the most common and signature moves of all queen's pawn games, but what purpose does it serve?
Openings are a lot about taking control over the centre and not conceding it easily to your opponent, so when white plays 1.d4, they're claiming control over dark squares, namely e5 and c5, similarly, black replying with 1...d5 they're reciprocating by controlling c4 and e4 (so light square control). And that brings us to the famous c4 move, which attempts to undermine black's control over light square, so whenever white manages to force black's hands into either taking on c4 or recapturing on d5 with a non-pawn piece, you could say white has achieved a small success in central control, which among other options may allow white to play e3-e4-e5 and take away more squares from black's minor pieces. These ideas should make it a bit more intuitive as to why, black recapturing with a non-pawn ought to be a strategic gain for white. Let's summarise with a diagram, in blue the desired central setup with d4-e4, and the green c4 the enabler, and in turn black's intends to keep maintain grip over d5 with e6/c6.

Now let's have a closer look at your game: 5...Bb4 by black is a terribly odd and poor move: black is playing rather inconsistently, first opting for an early queen-side development with b6 to fianchetto their c8 bishop, but then develop their dark squared bishop, temporarily ignoring the created light square weaknesses, in particular c6. Moreover, bishop developments before knights are possible but rather rare, in general knights are more easily developed (as their restricted movement makes their optimal development easier to resolve given a structure), and they in turn create useful space for the bishops. And your game makes for a perfect example of such careless development as it can be tactically exploited with an immediate Qa4+ which:

Forces Nc6, which is not only a non-ideal knight placement in this position (the structure tends to favour developments of the type Nd7-Bb7-Nf6-Be7 with an early c5 to challenge white's centre, impossible with a knight on c6) but it also allows white to force a queen recapture on d5 after cxd5.
After 7.cxd5, black can either take on c3 first with check, or take on d5 with Qxd5 immediately as the knight on c3 is pinned. Obviously, exd5 is not a choice as it outright blunders c6 since the queen will no longer be caged as it can take on d5 afterwards.
Not only white will have fully claimed the centre, but they will also be much ahead in development and black has a real struggle ahead to even meaningfully finish development (no prospect for active knights, open files and rook activity ...) while parrying white's upcoming threats, to showcase with one possible scenario, after 7...Qxd5 8.Bd3 Ne7 9.O-O Bxc3 10.bxc3 O-O 11.e4 Qd8 we reach the following position:

Note that black conceding the d5 pawn with either dxc4 or a non-pawn recapture would be acceptable provided they could maintain sufficient light square control with their minor pieces afterwards, e.g. a knight on f6 and a fiachetto'ed b7 bishop. The latter may further justify the opening of the long diagonal for creating active play against white's king.
Last but no least, at a rough basic level similar to our earlier discussions, there are openings where black even encourages white towards an early advancement of central pawns, which black aims to exploit by either fixing the structure and therefore inducing a weakness (like the King's Indian Defence) or by actively trying to undermine the central structure in order to create a weakened target (such as the Grünfeld Defence), all backed by an early kingside development.


Longest possible FEN What is the longest possible FEN? The reason for that question is, that  I am designing a PGN viewer (again), and I have noticed that the FEN is dependent on the width of the board (the FEN test area is placed below). So the following number of lines are necessary:

FEN width > 460: 1 line
FEN width > 240: 2 lines
FEN width < 240: 3 lines or more

But is that sufficient as a heuristic? If I would known how many characters a FEN string has as maximum, I could compute it.

Addition: I did some experiments with games, and did not found FENs longer than 72 characters. So the current answers are of course sufficient, but could someone provide a (legal) position that comes near those 90 characters?

The FEN consists of six parts (see definition of FEN here):

piece placement: at most 64 characters, one for each square plus 7 times "/" to delimit ranks = 71 characters
active color: one character ("w" or "b")
castling: at most 4 characters
en passant: one or two characters
half move clock
full move number

In addition there are 5 space characters between them.

So in total I count a maximum of: 71+1+1+1+4+1+2+1+x+1+y = 83 + x + y

x and y are the number of characters to represent half moves since the last capture/pawn move and the total number of moves respectively.

In most realistic games you'd have x=3 (after 50 moves = 100 half moves a draw can be claimed after 75 moves = 150 half moves it is a draw) and y=3 (allowing games up to 999 moves long. If you want to be on the safe side, taking x=3 (no pawn move or capture for 999 half moves max) and y=4 (games up to 9999 moves long).

This would leave you with a string of 90 characters, but read on...

Additional consideration 1 (en passant)

The first part of the FEN string can be 64+7 characters long. One possible position is:

b1q1k1n1/p1p1p1r1/1r1b1n1p/1p1p1p1P/1P1P1Pp1/P1P1P1P1/R1R1K1B1/N1Q1B1N1 w - f3 0 1

Note in particular, that it is possible to have en passant capture in such setup (thanks Fabian Fichter for pointing this out), i.e. to have a 2 characters en passant string and 64+7 characters for the piece placement.

Additional consideration 2 (castling)

Any of the four castlings is described by one character (to be compared with one character if no castling is possible).

In order for castling to be possible, neither king nor the respective rook can have moved. For queenside castling this does not create any problem, because e1 and a1 (e8 and a8) are squares of the same color and you can place pieces alternatingly similar to the example above.

However regarding kingside castling, if e1 and h1 (or e8 and h8) are occupied, this will break the structure and shorten the 1st part of the FEN string, by 1 for each color's kingside castling.

Additional consideration 3 (en passant and half move clock)

[Again due to Fabian Fichter]:

En passant is only possible if the last move was a pawn move. Any pawn move however resets the half move counter (5th part of FEN). If you compare one extra character for en passant (2 chars vs just "-") with two extra characters for the half move counter (3 digit number vs "0") the conclusion is, that in the longest FEN, en passant is not possible.

This reduces the string by 1.

Additional consideration 4 (50 or 75 move rule)

The game is drawn after 50 moves (if claimed) or at most 75 moves without a capture or pawn move. Captures shorten the 1st part of the FEN by 1 char, so clearly you don't gain anything with regard to the last part of the FEN string by extending the game via captures.

The maximum number of pawn moves (for a full board with 64+7 string for the first part of the FEN) should be 24, e.g. by moving every second pawn 1 square ahead and the other pawns two squares in two moves (=2*(4+8)=24). So the pawn moves can extend your game to 24*50=1200 or 24*75=1800 moves.

This shows that it is possible to have a 4 digit move counter without a forced draw and also that it is not possible to have 5 digit move numbers because the game would be drawn before. (even if captures are included you would only gain another 62*75=4650 moves, leaving you well below the limit of 9999 moves).

So the total maximum number should be 90 -
 2 (for castling) -1 (en passant vs half move counter) = 87 characters.

Note that all this holds for regular chess games. If you need to support any non-standard variants you might have to reconsider these numbers.


Estimating probability of player playing move in the opening For position you never played, book probability is perfectly fine for me. The question starts when you already played position x-times. I'm looking for function that will update book probabilities with your style. Obviously if you play 1.d4 in 97 games out of 100 games, probability of playing 1.e4 runs close to 0%. On the other hand, if you played some late position just once, it's nowhere close to 100% you will repeat the move. I could probably make some  workaround myself, but this looks like problem data scientists must have already solved, as it is applicable to virtually any discipline where you want to predict someone's behavior.

Edit: I think there should be one parameter <0;1> measuring how seriously we take book probabilities and how seriously we take players games. With one extreme being ignoring book and one being ignoring player's games.

Intuitively we should look at the player's games for early moves and book moves for later. This is because as we get further in a game, the number of possibilities increases, therefore the sample size of player games decreases. In this scheme, we are assuming that the player in question behaves as the average player does in the long run given the positions they usually seek from the opening.

You could use a rule of using the player's games if there are more than 5 to use, and using other players games otherwise.


Why is algebraic notation called algebraic? How does algebra relate to this chess notation?

Why do they call this chess notation algebraic?

I think that Jonathan Garber is right. Much of algebra has to do with equation in an x y coordinate plane which is very similar to the way that algebraic notation denotes specific squares on the board. I have however not been able to find any specific source of the information.


What is the easiest possible way to start teaching children how to play chess? As a followup to What is the earliest possible age to start teaching children how to play chess?, I'm wondering: What is the easiest possible way to start teaching children how to play chess?  The point is that at such an early age, it's possible, if not likely, that the best way to teach an adult would not apply to a young child. Any suggestions?

The easiest way depends on age.

If they are really young, just start simple with how a plain board and introduce the pieces one by one (where they go on the board and how they move). Then put all the pieces on the board and show how the pieces move together.

If they are a little older, I would play show them short games with tactical ideas and mating patterns.  No need to dwell too much on the opening yet or the endgame.  Stick to the fundamentals first and make sure they have a firm grasp on that.

You probably will also find some tips on http://www.chesskid.com and http://www.chesskids.com


Winning as white is a struggle! [Title "White to move"]
[FEN "5r2/5q1k/6pp/1p2P3/1P2p2P/6RK/3Q1P2/8 w KQkq - 0 1"]

I can’t seem to win here, no matter what I do. Is the position really that bad for me as White?

The position is roughly equal. The problem for both sides, but it is a little worse for white, is king safety. That is the overwhelming positional factor here.

Kg2 and Qd4 is the best plan for white here to counter the threat on f2. It is positionally mutually difficult to do anything since both queens and rooks must keep defending soft spots. Trying to do more, and you likely get mated.

Here is a short sample line with notes.

 [FEN "5r2/5q1k/6pp/1p2P3/1P2p2P/6RK/3Q1P2/8 w - - 0 1"]

 1. Kg2 {to defend f2} Qf5 {activating the queen a little} 2. Qd4 {also activating the queen a little, but keeping an eye on f2 at the same time} Rf7 3. Qb6 {keeping black thinking about the white queen taking on g6 and then mate} Kg7 {pass} 4. Kg1 {pass, and not much progress can be made.}


Meditation practice among the chess elite? My question is simple.  Do we know of any 2700+ caliber players that regularly cite meditation as part of their lifestyle / preparation?

It's not hard to find meditating chess players, but I'm wondering about its use in top practice and perhaps if there are any studies that have attempted to measure its effects.

I found these sources for "meditation" among the past 2 worlds champions:

Carlsen:
https://www.youtube.com/watch?v=ELoJbv4bCHw

Anand:
https://badrirag.wordpress.com/category/viswanathan-anand/

Q : Do you practise meditation and if so, how effective do you find it?

A:  I don’t meditate regularly and hence I do not know the extent to which it can help.

Based on my Google research, some chess players meditate, but I see no evidence proving that top chess players meditate more than the general population


Is there a list of ALL features that are available on some chess clock? Is there a list of all features that are available on some chess clock?

I played speed chess last week and somebody had an old clock with features I had never heard of before.

So add, delay, both, count up, count down, hourglass,  bell every 10 seconds,  restricted to occurring after some move number,  whatever.

What would be on  a complete list of all chess timer features?

I do not think that you will find a complete list that compares all features between all companies. The closest you might get would be an article that reviews chess clocks, and compares them. I will tell you how I picked my new clock, since it still involves finding the information you are seeking.

When I got back into chess in the last year, I bought a new digital clock since it was time, and I only had some nice old analog clocks. I went to the major manufacturers, DGT, VTEK, and Chronos, and their websites.

Virtually all chess clocks have these basic features today. Using a blitz game of 5-3 as an example, this is how they work:

Fischer’s clock – The clock starts at 5:03, runs down to 5:01 and after the move ends up on 5:04.
Bronstein’s clock – The clock starts at 5:03, runs down to 5:01 and returns to 5:03 after the move.
Time delay – The clock is paused at 5:03 and nothing changes after the move.

For more on this, I pulled this from this nice article.

Beyond that, most of the features have nothing to do with chess. They are more along the lines of how many pre-programmed time settings are there, how many personalized time controls you can program in, what is the quality of the materials it is made of, brand reputation, and is it FIDE certified?

Those things, you just have to compare from clock to clock, and there are a lot of reviews out there comparing chess clocks to guide you. You can also look at the manuals to get an idea.

I, ultimately, went with a DGT3000 primarily because it is FIDE certified, and is the clock that you see at all the international events. You can look at the manual here, and see a lot more about the features.


Software to train attacks-vision I'd like to train a sort of "chess vision". For a given position, I should find all the figures under attack, something very similar to schach-schlägerei: https://itunes.apple.com/de/app/id428235830

Unfortunately, this application is iOS-only. Suggestions for alternatives are welcome.

Chess Gym allows you to do that and much more (you can also try to find all the defended pieces in a given position). It's free and you can play without having to register.


When to use Clear Hash I am developing a program that analyzes games sequentially, i.e. one game after another.

Below are the parameters.

Engine: Stockfish 10

Threads: 2

Hash Table: 4000

Depth: 30

My question is about when to use the command: "setoption name Clear Hash."

Should it be used after each position is analysed? This means that each position would have a "fresh" hash at the beginning of the analysis.

Or should it be used after each game is analysed? What are the differences?

If your goal is to get the highest quality of analysis, then the short answer is "never".

The reason is that if you analyze similar positions within a game, then the existing hash table entries can still be valuable for move ordering and evaluation, because the same positions might be encountered somewhere in the search tree again.

If you switch to a new game, then the hash should be cleared, but in that case Stockfish already does it implicitly when it receives the ucinewgame command. In fact, in Stockfish ucinewgame does exactly the same as setoption name Clear Hash.


Battling the London System I seem to have fairly good success against the London system and the Colle using the Queen's Indian defense. Has there been any games at the Senior master level where the Queen's Indian has been used?

I set out to answer my own question with the help of two computers. A Dell desk top using Windows 7 and a Dell laptop using Windows XP. The desktop used Deep Fritz 12 and Fritz 11 was used on the laptop. I played the London opening against Deep Fritz 12 and it appeared to use the Semi-Tarrasch.  After I set-up the opening in Fritz 11, Deep Fritz 12 lost to Fritz 11. I wanted to try the Queens Indian. The second time I played the London system against Deep Fritz 12 Deep Fritz wanted to play the Grunfeld. I had to force it to play the Queens Indian. After 51 moves Fritz 11 resigned.

[Event "Blitz 45m"]
[Site "Independence"]
[Date "????.??.??"]
[Round "?"]
[White "Gyr_man/Fritz 11"]
[Black "Deep Fritz 12"]
[Result "*"]
[PlyCount "80"]
[TimeControl "2700"]
[fen ""]

1. d4 {0} Nf6 {0} 2. Nf3 {0} e6 {0} 3. Bf4
{0} b6 {0} 4. e3 {0} Be7 {0} 5. h3 {16} Bb7 {3} 6. Be2 {166} d5 {217} 7. Nc3 {
154} O-O {0} 8. O-O {134} c5 {0} 9. Ne5 {186} Nc6 {0} 10. Bb5 {151} Rc8 {0} 11.
a3 {70} cxd4 {83} 12. Bxc6 {90} Bxc6 {0} 13. Nxc6 {167} Rxc6 {0} 14. exd4 {97}
Bd6 {21} 15. Qd2 {61} Bxf4 {171} 16. Qxf4 {14} Qc7 {275} 17. Qg5 {155} Ne8 {123
} 18. Rfd1 {63} Nd6 {179} 19. Qg3 {6} Rc8 {60} 20. Ra2 {66} b5 {87} 21. Qf4 {52
} a5 {131} 22. Raa1 {10} Qd8 {122} 23. Rab1 {70} h6 {39} 24. Ra1 {70} Rc4 {177}
25. g3 {12} g5 {26} 26. Qf3 {63} Kg7 {0} 27. Kg2 {39} b4 {1} 28. axb4 {63} axb4
{0} 29. Na2 {53} Rxc2 {18} 30. Nxb4 {39} Rxb2 {0} 31. Nd3 {105} Rbc2 {0} 32.
Nc5 {100} Nf5 {45} 33. Qd3 {33} Rc4 {0} 34. Rdc1 {20} Ra8 {11} 35. Rxa8 {23}
Qxa8 {0} 36. Nb3 {34} Qa4 {34} 37. Ra1 {22} Qb4 {57} 38. Ra7 {11} Qb6 {40} 39.
Ra2 {20} Qc7 {5} 40. Qd2 {0} Nxg3 {29} (40... Nxg3 {7} 41. fxg3 {41} Rc3 {0}
42. Qf2 {59} Rxb3 {0} 43. Rd2 {22} h5 {38} 44. Rb2 {39} Rxb2 {2} 45. Qxb2 {19}
h4 {17} 46. gxh4 {8} gxh4 {27} 47. Qf2 {11} Qg3+ {7} 48. Qxg3+ {33} hxg3 {0}
49. Kxg3 {14} Kg6 {1} 50. Kf3 {26} Kg5 {4} 51. Kg3 {27} Kh5 {4}) *


What is the lowest possible rating you can achieve (if any)? This question comes from a lack of understanding of how ratings work.
What is the lowest rating you can get ( or does it never stop decreasing )?

If the Elo system is implemented in its purest form, there is no theoretical lower limit for a rating.

Practically though, every chess organisation implements its rating system a bit differently and often there are rating floors that constitute the lowest possible rating.

The USCF for example seems to have a rating floor of 100.


Why did Capablanca win a majority of games playing as black? The first-move advantage is said to make it slightly more likely for white to win. This is shown in many databases of chess games, such as chessgames.com which shows the following results:

White wins 294,068 games (37.57%)
Black wins 216,938 games (27.72%)
271,659 games are drawn (34.71%)

Despite this, Capablanca actually had a higher win rate when playing black compared to playing white. Of course there is always an exception to the rule, but what aspect of his play makes him different to all the other players of his time?

In Megabase 2016, Capablanca played 791 games as White and won 52.6% of them, and played 406 games as Black and won 48.5% of them, so he didn't win more as Black but it was surprisingly close.

The discrepancy between number of White games and Black games was surprising, so I broke out his simultaneous displays (in which he would generally be playing White). In his simuls, he played 304 games as White and won only 40.8% of them, and played 26 games as Black and won 34.6% of them.

When we subtract out the simul games, he won 292/487 = 60.0% of his games as White, and 188/380 = 49.4% of his games as Black.

In conclusion, I suspect that the unique aspect of his play was that he didn't try that hard in simuls.


Resources on the Ruy Lopez for White - why so few? The Ruy Lopez is one of the most popular chess openings for both sides after 1.e4, and despite this I feel like there are few good detailed resources for players of the white side wishing to play the main lines in the Ruy.

What makes this seem so strange to me isn't just the relative underrepresentation in comparison to popularity of the opening, but rather that it seems like there are plenty of good resources for white against other major replies to 1.e4 (for instance, GM Negi has personally managed to produce well-received, complete repertoire books against the French, the Caro and the Sicilian (and the somewhat obscure Philidor defense)). Also, I have noticed that there are complete repertoire books in some of the mainlines in the Ruy, but these seem to be from black's point of view as far as I can tell.

My question is therefore: why aren't there more resources on the mainline Ruy from white's point of view? Is it difficult for authors to find good lines for white to recommend, making them hesitant to publish anything (for instance the Berlin giving players on the white side too much of a headache)? Or are there other reasons, like the mainline Ruy being more easy to play from the white side, making authors feel like you're supposed to figure it out by yourself as white?

I personally think the task is too daunting.  There are so many defenses for Black to cover. Some sideline like the Worrall or the exchange Ruy Lopez are each full books on their own.
Secondly, the subtleties are highly abstract and difficult to explain in a book.  I think Karpov could write a book similar to his book on the English opening where he doesn't try to cover variations but instead just annotates a bunch of relevant GM games.


Can a player capture en passant two times in a row? Suppose that there are only two pawns that White can use to put the Black king in check that are on the board.
But in both cases, the pawns need to move past Black pawns, risking en passant capture to both pawns.

So, my question is this: Can an opponent capture en passant twice in a row, when two different sets of pawns are in play?

Yes, given that the opponent helps the capturing side, it is possible to capture en passant two times or more in a row
Here is a famous example from a real game. The score came from chessgames.com
You can find more such games here on Chess Stack Exchange.
[Title "Sergey Gennadyevich Kudrin-Rudy C Douven, GMA Baleares op, Palma de Mallorca Spain, 1989"]
[startply "59"]
[FEN ""]

1. e4 c6 2. d4 d5 3. Nc3 dxe4 4. Nxe4 Bf5 5. Ng3 Bg6 6. h4 h6 7. Nf3 Nd7 8. h5  Bh7 9. Bd3 Bxd3 10. Qxd3 e6 11. Bf4 Qa5+ 12. Bd2 Qc7 13. O-O-O Ngf6 14. Ne4  O-O-O 15. g3 Nxe4 16. Qxe4 Nf6 17. Qe2 Bd6 18. Ne5 c5 19. Rh4 Bxe5 20. dxe5 Nd7  21. Rg4 Rhg8 22. Re1 Qc6 23. Qe4 Nb8 24. Rf4 Rd7 25. Qh7 Rgd8 26. Ba5 b6 27. Bc3  Qd5 28. b3 b5 29. Kb1 b4 30. Bb2 f5 31. exf6 g5 32. hxg6 Rxh7 33. gxh7 e5 34. Rxe5 Qf7 35. Re7 Qf8 36. f7 Qxe7 37. f8=Q Rxf8 38. Rxf8+ Qxf8 39. h8=Q Qxh8 40. Bxh8 h5 41. Kc1 Kd7 42. Kd2 Ke6 43. Ke3 Kf5 44. f3 Nd7 45. Kd3 Nb6 46. Bg7 a5 47. Bf8 Nd7 48. Bd6 Ke6 49. Bc7 Kd5 50. c4+ bxc3 51. Kxc3

For an extreme showcase, here is a chess problem that features 7 en passant captures in a row! My source for it is Yet Another Chess Problem Database.
[Title "Milan Velimirovic, Novi Temi 1979, 1st Prize, Mate In 10"]
[FEN "r7/pppppppN/8/1PPPPPPP/1n5k/R5N1/3n2K1/8 w KQkq - 0 1"]

1. Ra4! a5 2. bxa6 b5 3. cxb6 c5 4. dxc6 d5 5. exd6 e5 6. fxe6 f5 7. gxf6 g5 8. hxg6 Ne4 9. Rxb4 Kg4 10. Rxe4#


Continue the Attack, Or Meet the Positional Threat? In the league last night the following position came up:

[Date "2017.10.26"]
[White "Ian Bush"]
[Black "Not Ian Bush"]
[Result "1/2-1/2"]
[StartPly "28"]
[FEN ""]

1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 c5 5.a3 Bxc3+ 6.bxc3 Qc7 7.Nf3 Nc6 8.Bd3 c4
9.Be2 Bd7 10.O-O O-O-O 11.a4 f6 12.Bf4 f5 13.Bc1 h6 14.Ba3 Be8 15.Qb1
    ( 15.Nd2 Qa5 16.Nb1 Nge7 17.Qc1 )
15...g5 16.Qb2
    ( 16.Nd2 )
16...Bh5 17.Rfb1 Bxf3 18.Bxf3 g4 19.Be2 h5 20.a5 Nh6 21.Bd6 Qd7 22.a6
    ( 22.Bc5 a6 23.Qc1 Nf7 24.Rb6 )
22...b6 23.Qb5 Nf7 24.Bc5 Qc7
    ( 24...Ncxe5 $1 )
25.Bxb6 $1 axb6 26.a7 $2
    ( 26.Qxb6 )
26...Nxa7 $2 27.Qa6+ Qb7 28.Qxa7 Qxa7 29.Rxa7 Rd7 30.Ra6 Rb7 31.Rbxb6 Rxb6
32.Rxb6 Kd7 33.Rb7+ Ke8 34.f3 Rh6 35.Rb8+ Ke7 36.Rb7+ Kf8 37.Rb8+ Kg7 38.
Rb7 Rg6 39.Kf2 Kf8 40.Rb8+ 1/2-1/2

I played 15. Qb1 and after various adventures and a fun game it ended a draw. And Qb1 is Stockfish's choice in this position, followed by the related a5, Qd2 and Qc1, in human terms it agrees with my plan of blasting through the Queen side.

However on reflection in the cold light of day I'm wondering if 15. Nd2 (as indicated) may be better to first meet the positional threat he has of swapping off his bad bishop for my good knight via Bh5 (also relieving a little cramp in has camp). Yes I lose a tempo or two for my attack, but I'll get some of it back when he has to move his queen back from a5, and I gain the opportunity to sac a piece for 2 pawns on c4 so bringing a second minor piece into the attack - and so giving my white squared bishop at least some purpose in life, even if it is only self-immolation.

So what do people think is better Qb1 or Nd2? Is this the kind of long term thing that computers aren't that great at? Or should I just trust the digital monster?

I think you are asking the correct question at the wrong move.  12.Bf4 is probably questionable and after 12...f5 you need to think about countering Black's kingside expansion.  A move like 13.Ng5 looks strong, a possible line being 13...Rf8 14.h4 h6 15.Nh3.  Then you can reroute the Bishop, put the pawn on h5 and Nf4 with a bind.

It is probably too late to thwart Black's light squared bishop with 15.Nd2 (which just looks ugly to me) as you are now having to deal with a kingside pawn storm but 15.Ne1 looks much better.  The idea is to play g3 and reroute the knight via g2 at some point.


Why is it necessary for black to defend e5 pawn after 1. e4 e5 2. Nf3? Why is it necessary for black to defend the e5 pawn after 1. e4 e5 2. Nf3? What do you think of 1. e4 e5 2. Nf3 a6 3. Nxe5 d6? Now white should move his knight to c4, d3 or f3 and black can develop more pieces.

It's not necessary; the solid Petrov's Defence continues with the counterattack 2... Nf6. There's also a less stable option in 2... f5, the Latvian Gambit but it rarely sees play at the top level.

Otherwise, the real problem for Black is not the knight on e5. It's the fact that you're giving away a center pawn without any compensation whatsoever. If you want to develop pieces, you're even better off playing 2... Bc5 than 2... a6.


Which is the World's largest chess club? Most chess clubs in my area struggle to gather more than 30 federated members with only one club past the 100-member count in a territory of 8 million people.

Which is the largest physical chess club in the World and how many members does it have?

Marseille Échecs (831 members)

According to the French Chess Federation, Marseille Échecs is the largest French club, totaling 831 officially registered players.

Two other French clubs have more than 500 members, in the cities of Bois-Colombes (612) and Villepinte (584), both near Paris.