How come it's actually Black with the advantage here? I was analyzing a recent game of mine, and I noticed something interesting. After I blundered back a bishop on move 16, the evaluation was -3.4, which is still strongly winning for Black.
[White "White"]
[Black "Black"]
[Result "0-1"]
[WhiteElo "1700"]
[BlackElo "1500"]
[fen ""]

1. e4 c5 2. f4 { B21 Sicilian Defense: McDonnell Attack } b6 3. Nf3 Bb7 4. Nc3 a6 5. Bc4 e6 6. O-O d5 7. exd5 exd5 8. Be2 d4 9. Ne4?? { (-1.03 → -4.31) Blunder. Nb1 was best. } Bxe4 10. d3 Bb7 11. Ng5 Be7 12. Bf3 Nc6 13. Re1 Nf6 14. Qe2 O-O? { (-5.42 → -3.17) Mistake. Qd7 was best. } 15. Bxc6 Bxc6 16. Qxe7 Qd5 17. Nf3?! { (-3.25 → -5.04) Inaccuracy. Qe2 was best. } Rae8 18. Qc7 Rxe1+ 19. Kf2? { (-4.63 → -19.29) Mistake. Nxe1 was best. } Ree8 20. Qxb6 Ng4+ 21. Kg3 Ne3 22. Qb3 Nf5+ 23. Kf2 Qd7 24. Bd2 Bxf3 25. gxf3 Nh4 26. c4 Qh3 27. Qd1 Qxh2+ { White resigns. } 0-1

How is this so, given that the material had evened out? Obviously, if it's not due to material, it must be due to something positional, but even then I'm not very convinced. After move 16, White owns the e-file and maybe even the 7th rank. They also has a knight on g5 which, to me, is a bit worrisome (should it not be?), and it's supported by a pawn and a bishop. What merits such a strong evaluation for Black?

White's actually quite close to busted in that position after 16...Qd5. Of the two points you bring up, note that White doesn't actually control the e-file because Black is ready to play a rook to e8 and drive White's major pieces away. The knight on g5 looks good, but it's also vulnerable to being kicked by ...h6 and it's not threatening anything yet. Otherwise, White's king is dangerously exposed on the long diagonal since Black already has a bishop on the diagonal and since White no longer has f3. Finally, White's queenside is undeveloped. Granted Black's a8-rook isn't developed either, but it can jump into the fray much quicker.
Consider, checkmate is threatened on g2 and White has only a few ways to defend it:

17.Re2 is the easiest to refute because 17...Rfe8 wins either a rook or the queen.
17.Nf3 is also terrible. Again Black plays 17...Rfe8, and after 18.Qc7 (or where else is White going to put the queen?) Black plays 18...Rxe1 19.Nxe1 (forced) 19...Rae8 (developing with tempo) 20.Nf3 (still forced) Re2. Black's pieces are overwhelming White's king while White's queen, bishop and rook are all spectators. An immediate threat is 21...Rxg2+ 22. Kxg2 Qxf3 and checkmate.
That leaves 17.Qe2, which is the least evil but still not good enough. Black again plays 17...Rfe8, forcing 18.Ne4 (all other moves either lose material or get mated on g2), and then the Knight is pinned. Black has a variety of promising ideas such as 18...Qf5 intending to take on e4, or 18...Nd7 intending ...f5 to win material.

By the way, it's striking how much of Black's advantage stems from the fact that White's queenside is undeveloped, and by extension the rook on e1 is undefended (once ...Rfe8 kicks the queen away). Move White's c1-bishop to d2, and Black's advantage drops to about -1.0.


Longest DTC in the endgame KQPKQ depending on the place of the white pawn I remember some statistics by Guy Haworth from the endgame KQPKQ (queen + pawn vs queen).

One of the statistics was the maximum DTC depending on the place of the white pawn (due to symmetry, it can be assumed that the pawn is on the queenside), but I cannot find it anymore.

Does anyone know where the statistics are?

I watched a Karsten-Mueller-DVD about this endgame and he stated that the bishop pawn gives the best winning chances. Perhaps, the statistics can approve this claim.

Here is a partial answer.

The paper Chess Endgames: Data and Strategy by Tamplin and Haworth reports, among other things, the maximum depth-to-conversion (DTC) and depth-to-zeroing (DTZ) among winning KQPKQ positions. Table 1b in the appendix indicates a maximum DTC of 114 among winning white-to-move positions, and Table 2a indicates a maximum DTZ of 71 for the same.

That article unfortunately does not include separate maximum DTC or DTZ metrics for the 4 respective queenside pawn options, but I can at least confirm that the maximum DTZ of 71 involves a rook pawn, and this maximal example was already given in Thompson's pioneering 1986 tablebase paper Retrograde Analysis of Certain Endgames. On p.138, the following position and maximal play line are indicated:

[Event "Thompson 1986"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "KQPKQ"]
[Black "Maximum DTZ"]
[Result "1-0"]
[FEN "8/q7/P6k/Q7/8/8/8/6K1 w - - 0 1"]

1.Kg2 Qg7+ 2.Kh1 Qf6 3.Qd2+ Kg7 4.Qd7+ Kg6 5.Qd3+ Kg7 6.Qg3+ Kf8 7.Qb8+
Kf7 8.Qc7+ Kg6 9.Qc4 Qf3+ 10.Kh2 Qe3 11.Qf1 Qe5+ 12.Kh1 Qh8+ 13.Kg2 Qa8+
14.Kg1 Qa7+ 15.Kh1 Qd7 16.Qf2 Kh5 17.Qe2+ Kg6 18.Qe4+ Kh5 19.Qc4 Qa7 20.
Qe2+ Kg5 21.Kg2 Qd4 22.Qf2 Qe4+ 23.Qf3 Qd4 24.Qe2 Kg6 25.Qb5 Qe3 26.Kf1
Qe4 27.Kf2 Qd4+ 28.Kf3 Kh6 29.Qc6+ Kg7 30.Qc7+ Kg6 31.Qg3+ Kh5 32.Qh3+ Kg5
33.Qe6 Qd1+ 34.Qe2 Qd5+ 35.Kf2 Qf5+ 36.Kg1 Qb1+ 37.Kg2 Qg6 38.Qc4 Kh5+ 39.
Kf2 Qf6+ 40.Ke3 Qe5+ 41.Kd3 Kg5 42.Kc2 Qe3 43.Kb2 Kg6 44.Qb5 Kh6 45.Kc2
Qe6 46.Kc3 Qd6 47.Kc4 Kg7 48.Qg5+ Kh8 49.Qh5+ Kg7 50.Qg4+ Kf7 51.Qf5+ Kg7
52.Qc8 Qf4+ 53.Kb5 Qf6 54.Qc6 Qb2+ 55.Kc5 Qf2+ 56.Kd6 Kg6 57.Kd5+ Kh7 58.
Qc7+ Kh8 59.Qc3+ Kh7 60.Kc6 Qf5 61.Kb6 Qe6+ 62.Kb7 Qe4+ 63.Kb8 Qb1+ 64.Kc7
Qa2 65.Qc6 Kh8 66.Kb8 Qb3+ 67.Qb7 Qg3+ 68.Ka8 Qh3 69.Qc6 Qg4 70.Qc3+ Kh7
71.a7 1-0


Bird's opening problems I've played the reversed Leningrad Dutch for some time, and I have the problem that when I play Nd2, Black forks my rook and queen on f6->g4->e3. I never get to push my e-pawn before Black forks me in some cases. Is there any solution to this problem?
Here is a sample line.
[FEN ""]

1. f4 d5 2. Nf3 c5 3. g3 Nf6 4. Bg2 Nc6 5. O-O e6 6. d3 Bd6 7. Nbd2 Ng4 ( I have wasted a move on Nd2.)

You have some options.  You could abandon 7. Nbd2 because it allows 7. ... Ng4; the standard choices in the main line are 7. Qe1, 7. c3, and 7. Nc3, much like the regular Leningrad Dutch.  If Black plays Ng4 while you still have e3 covered by the Bc1, you can simply proceed with your plan to push e2-e4, and maybe later kick the knight with h2-h3 to get an attack going on the kingside.  Just make sure to keep an eye out for tactics on the a7-g1 diagonal as long as Black has a knight on g4; Bird's Opening can get ugly for White fast if you miss seeing a tactic.  You'll still need to pay attention to e3; Black's main try in the strongest lines is to play d5-d4, possibly following up with Nd5, and eventually you'll need to be prepared to play against that.  If your opponents are still gifting you e6 setups though, that might be a ways off.
In the specific position you've shown with Black's lackluster e6 setup, you have the option of going straight for 7. e4 as @bof and @pulsar512b discussed, but that idea won't ordinarily be available if Black plays more demanding lines.
If you're dead set on making 7. Nbd2 work instead, then 7. ... Ng4 8. Nb3 doesn't look like the absolute end of the world to me, but the positions aren't pleasant and Black is calling the shots.


According to official FIDE rules, when queening a pawn, can you pause the clock? I have heard that you are allowed to pause to clock to find your queen. Is this true?

You may stop the clock if the piece that you wish to promote to is not at hand:

  6.12.b. A player may stop the chessclock only in order to seek the arbiter’s assistance, for example when promotion has taken place and
  the piece required is not available.


Black Lion opening plans for White's 5. Bc4 line The Black Lion is a line that can be transposed from a Philidor or Pirc defense. I play with White this line.
[FEN ""]
1.e4 e5 2.Nf3 d6 3.d4 Nf6 4.Nc3 Nbd7 5.Bc4 Be7 6.O-O c6 7.a4 Qc7 8.Re1 h6 9.h3 g5 10.a5 Rg8 11.b4 g4 12.hxg4 Nxg4 13.Bb3 Nf8 14.a6 b5 15.d5 Bd7 16.dxc6 Bxc6 17.Nd5 Qd8 18.c4

As you can notice, all my play relies on opening up the queenside and occupying the d5 square. However, when Black plays 9 ...a5 shutting all my counterplay on the queenside. I really don't know what to do. Black would just maneuver his knight as usual to f8, and then something like Rg8 and g5 with a formidable kingside attack on White. I would really appreciate it if somebody can give me some lines with clear plans.

The first thing to note is that 9. h3 is a minor mistake if your intention is to play a queenside attack. It is a diversion from your plan. It would make more sense if your plan were to attack through the center with moves like Qe2, Be3, Rd1, de, etc. In that case it would create a safe spot for the bishop on e3 by denying g4 to the black knight. All h3 is does in the plan you play is to accelerate the black kingside pawnstorm by creating a pawn lever for a later black g4.
Instead in the final position above follow Jonathan Rowson's advice and "talk to your pieces". In particular the bishop still at home on c1. Why are you attacking before you have completed your development? Particularly why are you attacking the opposite side of the board to where the enemy king is? Find a plan which involves completing your development by finding a square for the c1 bishop.
One suggestion would be to follow a plan played by Aron Nimzowitsch 100 years ago which involves fianchettoing the c1 bishop with threats of a knight sacrifice on e5 if black plays Nf8. Here are the moves up to where he has a big advantage:
[title "Nimzowitsch - Marco, Gothenburg 1920"]
[fen ""]

1.e4 e5 2.Nf3 d6 3.d4 Nf6 4.Nc3 Nbd7 5.Bc4 Be7 6.O-O h6 7.a4 c6 8.b3 Qc7 9. Bb2 Nf8? (9...g5! 10. Re1 Rg8 11. dxe5 dxe5) 10. dxe5 dxe5 11. Nxe5 Qxe5 12. Nd5 Qd6 (12...Qxb2 13. Nc7++) 13. Ba3 (13. e5 Qxe5 14. Re1 Ne4 15. Rxe4 Qxe4 16. Nc7++) cxd5 14. Bxd6 dxc4 15. Bxe7 Kxe7 16. e5 N6d7 17. Qd6+


How strong is each level of Atari 2600's Video Chess? I used to play Video Chess on Atari with my dad when I was a kid.  What is the approximate FIDE rating of each level?

Atari 2600 has bugs which make the higher levels unrateable. It is reputed to be slightly better than Microchess, according to a chess.com article.

Atari had a very limited book which makes it weaker than current approaches.

An ESTIMATE of the strength is as follows:

Level Time Rating(?):

8        10       700

1        15       800

2        30      1000

3        45      1100

4       165      1300

5       195      1350

6       720        ??

7     36000        ??


Why is it a mistake to capture the forked rook? In a recent game, I forked a queen and rook with a knight. After seeing no immediate threats from 8. Qf4 I immediately captured with 8. ...Nxb3. Apparently this was quite a mistake (a 213 centipawn evaluation drop), but it's not clear to me why the material advantage from Nxb3 is inferior to Stockfish's recommendation of Nxc2, let alone far superior.
[White "White"]
[Black "Black"]

[fen ""]

1. e4 c5 2. Bc4 { B20 Sicilian Defense: Bowdler Attack } b6 3. a4 Bb7 4. Qf3 e6 5. Ra3? { (-0.77 → -2.15) Mistake. d3 was best. } a6 6. Rb3 Nc6 7. Nh3? { (-2.78 → -5.30) Mistake. Re3 was best. } Nd4 8. Qf4 Nxb3? { (-5.02 → -2.89) Mistake. Nxc2 was best. } 9. Ng5?? { (-2.89 → -6.87) Blunder. Bxb3 was best. } f6 10. Nxe6 dxe6 11. Bxe6?! { (-5.59 → -10.58) Inaccuracy. Bxb3 was best. } Nd4 12. Bg4 Nxc2+ 0-1

What am I missing here? Why shouldn't Nxb3 be played (or maybe, why is Nxc2 far superior)?

The key point is that taking the rook reduces your positional advantage.

Your knight is active but the rook is passive;
With your knight on d4 the squares the rook can move to are extremely limited. After 8. ... Nxc2+ 9. Kf1 h6, only f3 and g3 are better squares for the rook. However, with the advancement of pawns on the king side, the queen will be chased away and the development of Nf6 will trap the rook. This will gain both the material advantage and the increasing positional advantage.

This is reflected in the Stockfish evaluation as Nxb3 yields -2.3, with the -2 coming from the material whereas Nxc2+ yields -3.8.


how to evaluate the position inside the search function using PVS Algorithm with Quiet search and zero window search what should the range of the score be (-infinity, infinity ) could it be as small as (-16000,16000) and what should the search return if it's a stalemate or checkmate for me or for the other side ?
I tried reading the source code of different engines but there is too much addition(heuristics and such) that make it too difficult for me to understand anything.

the question in another for given this PVS algorithm how and where should I place checking for chaeck/stale mate and what score should I return ?

int PVS(alfa,beta,depthleft) {
   if( depthleft <= 0 ) return qsearch(alpha, beta);

// using fail soft with negamax:
make first move
bestscore = -PVS(-beta, -alpha, depthleft-1);
unmake first move
if( bestscore > alpha ) {
   if( bestscore >= beta )
      return bestscore;
  alpha = bestscore;
}

for( all remaining moves ) {
  make move
  score = -PVS(-alpha-1, -alpha, depthleft-1); // alphaBeta or zwSearch
  if( score > alpha && score < beta ) {
     // research with window [alpha;beta]
     score = -PVS(-beta, -alpha, depthleft-1);
     if( score > alpha )
       alpha = score;
  }
  unmake move
  if( score > bestscore ) {
     if( score >= beta )
        return score;
     bestscore = score;
  }
}
return bestscore;
}

I wasn't sure where to post this question here or on stack overflow so please migrate it as you see fit

where should I place checking for chaeck/stale mate

Right before make first move: there is no first move!


What is a more efficient thinking process? I'm a bit of a perfectionist and strive to make the best move every game. As a result I think I expend too much brain power throughout the game and get burned out or overwhelmed by the possibilites, for example in the opening I would try consider all my opponents responses of which there are many in the opening, sometimes I feel habits such as these are unnecessary and are just a waste of energy. What is the most correct way to expend your mental energy in a chess game?

When you learn an opening you learn sequences of moves and the ideas behind those moves. If your opponent follows "book" then you don't have too much to think about. Probably just "Which variation am I going to play today? Am I feeling like a quiet strategic game or a wild tactical game?"

If your opponent plays a move you are not familiar with then there are two questions and two situations to cover.

1) You are playing a sharp, tactical opening where there are lots of threats and he didn't counter your threat and isn't counter threatening anything. In that case carry out your threat!

2) You are playing a quieter opening in which you are both just developing your pieces. In that case, after checking for threats, ask yourself if his move stops you developing the way you wanted. If it doesn't then carry on. If it does then work out how you now need to develop the rest of your pieces.

In the middlegame it is a bit different. When it is your turn you do need to calculate what you evaluate are your opponent's best replies.

When it is your opponent's turn it depends how many good looking possibilities he has. If it looks like just one or two forced or "best" replies then stay in your seat and calculate those. If it is a complicated position with lots of equally likely looking possibilities then either take a step back and look at the position from a long term strategical point of view or save your energy, go get a cup of coffee or glass of water or relax looking at other games whilst keeping half an eye on whether your opponent has moved yet.


What does [6/10]-611 stand for? I am using Chess for Android app by Aart Bik. Fairly easy to use and understand (and difficult to beat).

I get these numbers displayed below the noted moves and I think these are analysis symbols giving a summary of current position in terms of who is likelier to win. One example is in the question. Other examples are: [4/7]3, [3/7]95, etc.

Can someone interpret these numbers into English?

According to the online manual for the app,

  After each engine's move, the output [d/s]eval indicates a search depth d, a selective search depth s, and an evaluation in centipawns eval from white's perspective. For instance, the output [4/8]-103 indicates that the engine searched 4 plies ahead, with some variations even 8 plies ahead, and thinks that black is ahead by about a pawn.


Why did Bobby Fischer play the Queen's Gambit as White vs. Spassky? Why did Bobby Fischer play the Queen's Gambit as White in many games in the 1972 World Championship match vs. Spassky, although he almost never played it in any other tournament or match game?

Spassky had an entire squad of Soviet grandmasters trying to find holes in Fischer's repertoire. So it made a lot of sense to surprise them. He also avoided the sharp King's Indian and went for the Nimzo instead.

There are other examples for this strategy. Peter Leko, a 1.e4 player, switched to 1.d4 for his match against Kramnik. Changing the black repertoire is even more common: Gelfands Gruenfeld and Sveshnikov against Anand, Kramniks Berlin against Kasparov ...


How can white mate black in 4 moves in this particular game. How can white mte black in 4 moves in this game. This might be easy but I am a beginner.
(https://i.stack.imgur.com/r5n6R.png)

The king has no escape squares and, as is often the case in these puzzles, every move must be a check.

[FEN "r1br4/1p3qp1/p1kb3p/2NN1p2/1PPQ4/8/P5PP/R4RK1 w - - 0 1"]

1. b5+ axb5 2. cxb5+ Kxb5 3. Rfb1+ Kc6 4. Rb6#


Did Bobby Fischer castle with a pawn promoted to a rook? I once heard that Bobby Fischer pawn promoted to a rook, and then on a subsequent move, castled with that rook. I have been searching for the move history of this game, if it really did happen, but I haven't been able to find it on the Internet. Am I just searching for a rumor, or did this really happen? Where can I find the move history for this game if it really did happen?

There was a time when the FIDE rules didn't specify that a king and rook
need to be on the same rank in order to castle.  This meant that, assuming
the other requirements for castling were met, it was legal for White to
castle with a rook on e8 (or Black with a rook on e1), provided that rook
had never moved (which could only happen if it was a promoted pawn).
This interpretation was never intended, of course, and the wording has since
been fixed.

I've never heard of Fischer (or any other player) taking advantage of
this glitch in the rules, but it was used in at least one chess problem.


Fischer playing Greenblatt in 1977 Is there any information, apart from the three games, regarding Fischer playing the Greenblatt computer in 1977? Wasn't Fischer living in seclusion at that time? How did someone manage to have Fischer play? Is there any photo of the event?

TL;DR: In summary, the sources I've found of the match reference Fischer himself.

Fischer sent the game scores himself:

  Rumors constantly reappear about the possibility of his playing again or making public appearances, but the only published games that we know of since 1972 were against the Greenblatt program, and they were submitted by Bobby himself and published in the Computer Chess Newsletter. Bobby sent the scores of three games in which he massacred the computer. In his comments on the games, Bobby noted that the computer was very weak and that he could give it great odds and still beat it.

Source: csmonitor.com

The match was held in Cambridge, MA:

  In 1977, unbeaten chess champion Bobby Fischer played three games in Cambridge, Massachusetts against Greenblatt's computer program, and Fischer won all of them

Source: Wikipedia, referencing Bobby Fischer's biography

I haven't found contemporary images or information on how the match was arranged.


Historical motivation for the 1200-1800ish rating average Although there is some variation in rating systems (in chess), most systems put the starting value and the mean of all users somewhere around 1500. Some pools are higher, some are lower, but most have their means somewhere in the 1200-1800 range. As ratings only have relative meaning within their respective pools, scaling or translating all ratings within a pool will not make the rating system any less effective for assessing relative strength. So my question is: what is the historical reason that the means are usually in the 1200-1800 range? Which "natural" parameter choices led to these means? And why not e.g. 100, or around 0, with positive and negative ratings?
For newer rating systems that aim to replace older systems, I suppose the mean is just a consequence of trying to mimic the previous system as well as possible. Say Glicko replacing Elo, or Elo replacing whatever was before that. I've tried some digging, but some historical works are behind paywalls and I am unable to find the historical, initial motivation for parameters choices that led to these averages in the 1200-1800 range.
Any pointers to relevant (freely available) literature explaining this choice would be appreciated!
Edit: As pointed out, not all systems start out at 1500, and averages for e.g. USCF or FIDE ratings may not be exactly 1500. My question is specifically why, historically, someone chose approximately 1500 as the average or starting value (and not any other value), and who was the one that made this deliberate choice (rather than making the average be in the 1000-2000 range to mimic other systems). Maybe the initial choice was just "let's put beginner ratings at 1000" and the 1500ish mean followed from that, that's possible too; I'm just wondering what ultimately led to the 1500ish mean of many rating pools.
(If anyone has access to Elo's original book, maybe they could look up what motivated Elo to use something like 1500 as the baseline.)
Edit 2: While the formulas of the Glicko system may somehow incorporate 1500 as a "special" initial choice, observe that the Elo system is the predecessor and clearly does not need 1500 as the baseline. And surely Elo didn't choose 1500 as baseline only because Glicko would later "need" 1500 as the baseline.
So perhaps to make it more clear that I am not looking for tangential discussions about whether the 1500 value for Glicko is necessary, let me ask the closely related question to my original question: why did Elo use initial parameter choices that led to ~1500 as baseline? (That answer might be "because the predecessor to Elo used 1500 as baseline" so digging further may be necessary, but all discussions about Glicko's subsequent choices are irrelevant to this question about the historical motivation of Elo and its predecessors.)
Edit 3: As pointed out in the comments, sources suggest the Elo system was designed to give similar ratings/rating chances as the Harkness system used previously. So to find the answer to this question one has to answer the question: why did the Harkness system have/lead to 1200-1800ish rating averages?

The first chess rating system, the Ingo system used in Germany, had very different numbers because in that system lower is better.  So the ratings there have no relevance to the current scale used by modern rating systems.
The second chess rating system, the Harkness system used by USCF starting in 1950, already is calibrated almost the same as modern rating systems.  In the original USCF announcement of the rating system it clearly says Class D below 1500, Class C between 1500-1700, Class B 1700-1900, Class A 1900-2100, Expert 2100-2300 and Master 2300-2500.  This is the same as current ratings but shifted by 100 points.  Acording to Wikipedia, the Harkness system caused ratings to deflate which forced them to both move the rating cutoffs down by 100 points and to switch to Elo.  So Elo was originally calibrated to match the ratings of Harkness but adjusted down by 100.  Unfortunately I can't find any sources about how Harkness chose his calibration.  So unless someone has access to Harkness's private letters or similar sources, it is unlikely that we'll get a definitive answer.


Can a chess engine play like a particular famous player? Different players have different personalities and different playing styles. Mikhail Tal's style is different from Tigran Petrosian, just as Kasparov is different from Karpov. I am wondering if there is a chess engine that can play "like" a real famous chess player, both in the sense of playing strength and style. After all, playing against a "resurrected" Capablanca or Botvinnik will be an exciting idea.

This idea was very popular back in the days, some programmers used their best to create such engines, and they did achieve that (to a certain extend)
Some engines that you might want to check out are:
Rebel
ProDeo
ShashChess
Szint
Szint has more of 100 personalities classified in 3 forms.
Szint Training with personalities from 0 to 2600 of elo.
Szint GM with personalities of world champions and grandmasters.
Szint Settings with strong personalities done by other users.


How do you checkmate with the pair of bishops? How do you checkmate with the pair of Bishops and King versus King?

Are there any stalemates to look out for?

What are the key ideas / positions / tricks to make it work?

Thanks!

I always like to explain this in a visual way.

Basic Idea: Keep the bishops together. They form a large net (restricted area) from which the opponent king cannot escape.

Step 1: Push Opponent's King To Edge Rank or File

Keeping the bishops together and using the king for support, make the restricted area smaller to push the opponent's king back to an edge rank or file.

     [FEN "8/8/8/3k4/8/8/8/K2BB3 w - - 0 1"]

    1. Bd2 Ke4 2. Be2 Kd5 3. Kb2 Ke4 4. Kc3 Kd5 5. Bd3 Ke5 6. Be3 Kd5
    7. Bd4 Kd6 8.Be4 Ke6 9. Kc4 Kd6 10. Bd5 Ke7 11. Be5 Kd7 12. Kc5 Ke7
    13. Kc6 Kf8 14. Bf6 Ke8 15. Be6 Kf8

1. Bd2 Ke4 2. Be2

2...Kd5 3. Kb2 Ke4 4. Kc3 Kd5 5. Bd3 Ke5 6. Be3

6...Kd5 7. Bd4 Kd6 8.Be4

8...Ke6 9. Kc4 Kd6 10. Bd5 Ke7 11. Be5

11...Kd7 12. Kc5 Ke7 13. Kc6 Kf8 14. Bf6 Ke8 15. Be6 Kf8 (note: I intentionally chose the 13...Kf8 line because that is more instructive. For the 13...Kd8 line, please see the sample mates provided at the end).

Step 1 Accomplished!

Step 2: Push the Opponent's King to a Corner

In the above position, we shall choose the h8 corner. The key is to keep the opponent's king on the back rank while slowly taking away squares from the other side.

The idea now is to move the king over to the right hand side via Kc6-d5-e5-f5-g6 to cover f7 and then move the bishop to d7 to cover e8, thereby pushing the opponent's king to the corner.

   [FEN "5k2/8/2K1BB2/8/8/8/8/8 w - - 0 16"]

   1. Kd5 Ke8 2. Ke5 Kf8 3. Kf5 Ke8 4. Kg6 Kf8 5. Bd7 Kg8

Now, we can take control over f8, thereby pushing the opponent's king to the corner.

   [FEN "6k1/3B4/5BK1/8/8/8/8/8 w - - 0 21"]

   1. Be7 Kh8

Step 2 Accomplished!

Step 3: Checkmate the Cornered King

Here, it is important to be careful to avoid a common stalemate that occurs in this position.

We observe that White has to make a waiting move in order to challenge the g8 square with check, so that then after Kh8, Bf6+ would be mate.

And now the mate is easy.

    [FEN "7k/3BB3/6K1/8/8/8/8/8 w - - 0 22"]

    1. Be8 Kg8 2. Bf7+ Kh8 3. Bf6#

Below, I have included other types of checkmates that can occur if Black play's differently. I've also included the fastest mate from the original position which starts with 1.Bc3!

    [FEN "8/8/8/3k4/8/8/8/K2BB3 w - - 0 1"]

    1. Bd2 (1. Bc3 Ke4 2. Kb2 Kd3 3. Bf3 Ke3 4. Bd5 Kd3 5. Be5 Kd2 (5... Ke3) 6.
    Bd4 Kd3 7. Bc5 Ke2 8. Kc2 Kf1 9. Kd3 Ke1 10. Bg2 Kd1 11. Bf2 Kc1 12. Kc3 Kd1
    13. Bf3+ Kc1 14. Be3+ Kb1 15. Kb3 Ka1 16. Bd1 Kb1 17. Bc2+ Ka1 18. Bd4#) 1...
    Ke4 2. Be2 Kd5 3. Kb2 Ke4 4. Kc3 Kd5 5. Bd3 Ke5 6. Be3 Kd5 7. Bd4 (7. Bf4 Kc5
    8. Be4 Kb5 9. Be3 Ka6 10. Kc4 Ka5 11. Bc6 (11. Bb7 Ka4 12. Bb6 Ka3 13. Kc3 Ka4
    14. Bc6+ Ka3 15. Bc5+ Ka2 16. Kc2 Ka1 17. Ba4 Ka2 18. Bb3+ Ka1 19. Bd4#) 11...
    Ka6 12. Bc5 Ka5 13. Kd5 Ka6 14. Kd6 Ka5 15. Kc7 Ka6 16. Bb4 Ka7 17. Bb5 Ka8 18.
    Ba5 Ka7 19. Bb6+ Ka8 20. Bc6#) 7... Kd6 8. Be4 Ke6 9. Kc4 Kd6 10. Bd5 Ke7 11.
    Be5 Kd7 12. Kc5 Ke7 13. Kc6 Kf8 (13... Kd8 14. Bd6 Ke8 15. Be6 Kd8 16. Bf7 Kc8
    17. Be7 Kb8 18. Kb6 Kc8 19. Be6+ Kb8 20. Bd6+ Ka8 21. Bd5#) (13... Ke8 14. Bd6
    Kd8 15. Bf7 Kc8 16. Be7 Kb8 17. Kb6 Kc8 18. Be6+ Kb8 19. Bd6+ Ka8 20. Bd5#) 14.
    Bf6 Ke8 15. Be6 Kf8 16. Kd5 Ke8 17. Ke5 Kf8 18. Kf5 Ke8 19. Kg6 Kf8 20. Bd7 Kg8
    21. Be7 Kh8 22. Be8 Kg8 23. Bf7+ Kh8 24. Bf6# *


Why do houdini and stockfish give this seemingly stupid move? [fen "3r3k/1rp2p1p/4b2B/p3P1Q1/3q4/1P1P2P1/P4PBP/1R4K1 b - - 0 28"]

They both give Qxf2 as the best move. I used http://analysis.cpuchess.com/ with search time 10 seconds. It's black to move.

In the given position, Black ultimately has no way to avoid an impending checkmate, hence is lost no matter what. The engines you're consulting are just trying to push that unavoidable mate as far into the future as possible. 1...Qxf2+ does that the best; any other defensive tries lead to a quicker checkmate. For instance:

[Event "?"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "?"]
[Black "?"]
[Result "*"]
[FEN "3r3k/1rp2p1p/4b2B/p3P1Q1/3q4/1P1P2P1/P4PBP/1R4K1 b - - 0 28"]

1...Qxf2+
    ( 1...Rg8 2.Qf6+ Rg7 3.Qxg7# )
    ( 1...Qxe5 2.Qxd8# )
2.Kxf2 Rg8 3.Qf6+ Rg7 4.Qxg7# *


Who has the advantage here? Who has the advantage here? In general  whar will perform better in this scenario- 3 pawns vs. 3 pawns, or 4 pawns vs. 2 pawns?

Black is better here, but this is much more due to piece activity and coordination than to the pawn structure.

Once upon a time (i.e. a century ago), it was thought that such structures gave a big advantage in endgames for the camp with 3 pawns on the queenside - because in the long term they can create an outer passed pawn. However, this has been debunked in practice since the times of Alekhine (who would enter such endgames on either side as long as he had more activity) and in theory at least since the works of Shereshevsky (who notably analysed endgames by Capablanca and Alekhine). Many examples in (online available) chapter V of this book by Srodovsky. In a 2001 book, Glenn Flear showed that even in pawn endgames the queenside argument is not void but generally not the most important.

Here Black controls the only open file, enjoys centralised and coordinated minor pieces, is on move and has no pawn weaknesses while a2, f2 and e4 might become useful targets. wNa3 is offside, wBf3 is unprotected and restricted by its own pawn on e4, and white rooks are undeveloped.

After, say 1...Rd8 2.Rad1 Ne5 3.Be2 (or 3.Rxd6 Nxf3+ 4.Kg2 Nh4+ 5.gh4 Rxd6 -/+) Rd2, Black is clearly for choice. 1...Rd2 2.Rfd1 Ne5 3.Bg2 Rfd8 is similar.


How is notation done for similar pieces capturing the same piece? When a capture can be made by two rooks, or two knights, etc., how does the notation clarify which piece makes the capture?

For example, if two pawns, one at e4 and one at c4, capture a pawn at d3, the notation will say exd3 or cxd3, sure.  But if two knights capture the same piece, how is that notated?  Or for two rooks, or queens?  In the case of the knight, it would only say Nxd3, but that doesn't clarify which knight took the piece.

Your two knights are on d2 and f2.

Ndxe4, Nfxe4,

Your two knights are on f2 and f6.

N2xe4, N6xe4

Your three knights are on d2, f2 and f6 (you promoted a pawn)

Ndxe4, Nf2xe4, N6xe4


How can I load a position without kings into an engine? I would like to be able to do load a position into a whatever possible (advanced) engine without kings. For example, the goal of the game would be to annihilate all the possible pieces instead of checkmating the king, and/or the king isn't even on the board. I sometimes test that. One example is when I want to see if a rook can stop two pawns at the 6th rank (it can't, I figured that out). Is there, maybe, an engine for that?

For most such questions perhaps a chess problem engine like Popeye can easily solve it.
However, the kind of goals your question is indicating like extinction of opponent pieces can also be set in configurable chess variant engines, e.g., Fairy-Stockfish or Sjaak II. I would assume that in most cases this will be the easier and faster solution, assuming that the problem is within the scope of the possible rule configurations.


Why are there separate tournaments for men and women? Why are there separate tournaments for men and women?

It is obvious that in physical sports men have a huge advantage, but what is the reason why in chess we differentiate by gender?

Chess as an activity is not appealing to many women. Because there are so few women in open tournaments, it can be quite intimidating for a girl or woman to start playing the game. Imagine being one of the 1-3% of female players at a large open tournament. They receive constant attention and stares (it is much worse if they are conventionally attractive). Some women like this or are not horribly pushed away by it. Many are.

Thus, girls-only tournaments were born. In the US, there is a National Girls Championship every year near Chicago which attracts 200+ participants. This is a place for them to play without having the pressure of being basically a foreign entity at most open tournaments. I think that scholastic tournaments for girls are a very positive part of the chess world.

On the other end of the spectrum, and what I don't like, is the structure of the Women's World Championship, Women's Olympiad and various national women's championships.

My basic issue with these events is that they essentially encourage top women to get to a certain point (about 2500 Elo) and then stop improving. Take the history of Olga Girya (http://ratings.fide.com/hist.phtml?event=4195752) for example. I count 23 events that she has played since Novemeber 2012-the last time that she played in an open tournament. In many of those 23 she played not a single woman that was higher rated than herself. She has been making plenty of money, but her growth as a player has been stunted by playing in such a closed pool.

Irina Krush, in the US, recently made GM. She has been playing in US Women's Championships since she was 14 and has been one of the top two or three seeds for maybe the last 10 years. How much better would she have been if she had instead been competing against the best players in the country in the Open championship? I think it is almost unquestionable that playing against inferior opponents so often been a detriment to her improvement.


Why is b4 the only move suggested by every chess engine? The only move suggested here by every chess engine is 17. b4

Can anyone please advise why is it so important?

[fen "r3k2r/ppp2pp1/7p/3pP3/3P2b1/5N2/RP1KBPPP/7R w - - 0 1"]

Black is down material but still has some strength. The most obvious one is that he has a pawn majority on the queenside, meaning potentially passed pawn if he manages to push his majority. So Black's plan will be to put both rooks behind the pawns and go for ...a5-a4, ...b5-b4 etc...

In a very simple way White can fight against Black play (it's prophylaxie) by pushing b4 preventing ...a5 and ...c5.
Moreover if we manage to push b4-b5, the pawn on a7 will now be a weakness so we can attack it (doubling rooks on a-file).


What is the longest known stalemate your opponent in x-moves problem? What is the longest known stalemate your opponent in x-moves problem where the given stalemate is the fastest one from the initial position? A win is not possible, but stalemating your opponent so they can't move is, and any other draw takes at least as many moves.

The solution does not have to be unique. The stalemating side will try to keep the game as short as possible, while the to-be-stalemated attempts to prolong it.

Here is an example of such a "stalemate your opponent" problem that is in 2 moves long.

[FEN "5k1K/8/7P/8/8/7b/8/8 b - - 0 1"]
[startflipped ""]

1... Bf5 2. h7 Kf7.

Another example is this with White to move. It is the record for White having only a king.

[Title "CJ Morse, The Problemist 1985"]
[FEN "8/ppp1p3/4p3/4p3/8/8/1pp5/brk1K3 w - - 0 1"]

1. Ke2 e4 2. Ke1 e3 3. Ke2 e5 4. Ke1 e2 5. Kxe2 e4 6. Ke1 e3 7. Ke2 e6 8. Ke1 e2 9. Kxe2 e5 10. Ke1 e4 11. Ke2 e3 12. Ke1 e2 13. Kxe2 c6 14. Ke1 c5 15. Ke2 c4 16. Ke1 c3 17. Ke2 b6 18. Ke1 b5 19. Ke2 b4 20. Ke1 b3 21. Ke2 a6 22. Ke1 a5 23. Ke2 a4 24. Ke1 a3 25. Ke2 a2 26. Ke1

Can anyone find a longer fastest stalemate your opponent in x-moves problem than the 35-move one below that I created?

The following thirty five move position is the longest position I could create.

White basically checks with four knights on c2 before blocking the black pawns with the king and knight on h1 while keeping the black king boxed in on a1. I tried extending this by adding another white knight on a3 to check on c2 but a black queen or black bishop cannot be added to capture on c2 since black still has eight pawns and there would be no square to place a black knight on to capture on c2.

[FEN "8/p1p2p1p/5pbp/8/qN1N4/4N2p/pr1r4/k1K1N2N w - - 0 1"]

  1. Nbc2 Bc2 2. N4c2 Rbc2 3. N3c2 Rc2 4. Nc2 Qc2 5. Kc2 h2 6. Nf2 h5 7. Nh1 h4 8. Nf2 h3 9. Nh1 h6 10. Nf2 h5 11. Nh1 h4 12. Nf2 f5 13. Nh1 f4 14. Nf2 f3 15. Nh1 f6 16. Nf2 f5 17. Nh1 f4 18. Nf2 a6 19. Nh1 a5 20. Nf2 a4 21. Nh1 a3 22. Nf2 c6 23. Nh1 c5 24. Nf2 c4 25. Nh1 c3 26. Nf2 h1=Q 27. Nh1 h2 28. Nf2 h3 29. Nh1 f2 30. Nf2 f3 31. Nh1 f2 32. Nf2 h1=Q 33. Nh1 h2 34. Nf2 h1=Q 35. Nh1


Chess book for kids (9-11 y.o.) Are there any chess books accessible for kids in the 9-11 age range that don't waste the first half of the book teaching how the pieces move, castling rules and en passant capture? I am expecting some basic principles of opening theory, strategies for the middle game (pawn structure, open files, long diagonals, doubled rooks, rook on 7th rank etc.), tactics (skewer, fork, discovered attack) and end game tips.

Winning Chess Strategy for Kids by Coakley is EXACTLY what you want.

Barely a few pages explaining basics. Then tons of practical content that even adults will find useful.   Wastes no time in getting intermediate lessons in strategy/tactics presented in an astonishingly kid-friendly way. :)


What do you do when you put your king in check and you don’t realise? I moved my king as I wanted it to be in a safer location and after I did my turn my opponent realised that I put my king in check by accident and as the rules state you cannot put your king in check we did not know whether we should go back to my last turn or if my opponent had won the game.

You noticed immediately, which makes it very easy because in this case the rules are the same (apart from time penalty) for all forms of chess. In the first instance you have to take back the illegal move and make a legal move. If possible you have to move the piece you touched. So, if your king could legally move to another square that's the move you would have to make. If it could legally move to several squares then you could choose between them.

For a first offence your opponent gains time on the clock. At blitz this is 1 minute and for standard and rapid it is 2 minutes. A second offence loses the game. But note that these penalties only apply if you pressed the clock before your opponent noticed and told you. If you did not press the clock then there is no penalty. You just have to make a legal move with the piece you touched.

The rules governing this are the FIDE Laws of Chess. This is what they have to say:

  7.5.1  An illegal move is completed once the player has pressed his clock. If during a game it is found that an illegal move has been
  completed, the position immediately before the irregularity shall be
  reinstated. If the position immediately before the irregularity cannot
  be determined, the game shall continue from the last identifiable
  position prior to the irregularity. Articles 4.3 and 4.7 apply to the
  move replacing the illegal move. The game shall then continue from
  this reinstated position.

  7.5.5   After the action taken under Article 7.5.1, 7.5.2, 7.5.3 or 7.5.4 for the first completed illegal move by a player, the arbiter shall give two minutes extra time to his opponent; for the second
  completed illegal move by the same player the arbiter shall declare
  the game lost by this player. However, the game is drawn if the
  position is such that the opponent cannot checkmate the player’s king
  by any possible series of legal moves.

Those are the rules for standard time control where the moves are being written. Because the moves are being written down it doesn't matter if the illegal move is noticed after several more moves were played, you still have to go back to the position when the illegal move was made and make a legal move instead.

For rapid and blitz this usually isn't possible and so the rules say that the illegal move has to be flagged before the next move. Appendix A in the Laws deals with rapid and the rule says:

  A.4.2 If the arbiter observes an action taken under Article 7.5.1,
  7.5.2, 7.5.3 or 7.5.4, he shall act according to Article 7.5.5, provided the opponent has not made his next move. If the arbiter does
  not intervene, the opponent is entitled to claim, provided the
  opponent has not made his next move. If the opponent does not claim
  and the arbiter does not intervene, the illegal move shall stand and
  the game shall continue. Once the opponent has made his next move, an
  illegal move cannot be corrected unless this is agreed by the players
  without intervention of the arbiter.

Appendix B deals with blitz and that says:

  B.4 Otherwise, play shall be governed by the Rapid chess Laws as in
  Article A.2 and A.4.

So, the rules are the same as for rapid, but for the penalties:

  B.2 The penalties mentioned in Articles 7 and 9 of the Competition
  Rules shall be one minute instead of two minutes.


chess.com Analysis "Accuracy" - What score is computer like for a given rating? I have a few questions about engine use detection at online games on chess.com:

Let's say both players are rated 1800 on chess.com online play and
they make n number of moves in a game.

White has 90% accuracy due to very decent moves, while black has an accuracy of 97.5%.

  If n > 20 (less likely to be good moves by fluke), does this
  accuracy score mean that black cheated?

From my understanding the accuracy also depends on the number of moves made. For example, if you only made 3 moves and followed a well known opening your score will be 100% and that is not suspicious.

  Thus, at what n does the accuracy start to matter when it comes to
  detecting a cheat?

Chess.com seems to not act upon reports of cheating players.

  Does this mean that those players did not cheat?

  How to escalate the situation to avoid losing those valuable games?

For example, some players cheat in crucial games in tournaments where a win allows them to advance over you.

  What stops someone from turning on a chess engine, when they
  have a losing position, until they gain an advantage (at which point
  they play without the engine)?

This seems like it would be impossible to detect as there will be
typical moves (normal moves they make) from their previous games, with a few amazing moves sprinkled in.

I'm a 1400-1500 rated blitz player on chess.com. Looking through my archives, I see that just this month I had a 34 move game, at a 3 2 time control, where I was rated at a 97.4% accuracy. And I know I wasn't cheating.

When I look at my recent daily games (where I'm rated higher, around 1900) I see a 46 move game where I was rated at 99%.

You can't tell anything from a single game.


My chess AI makes the same repeated moves I've built a chess game engine using Minimax and when I play AI against the AI, everything goes fine(for sometime) until both the AI players make the same set of moves again and again.

Observe the moves made by the AI players in the move-log(Right panel).

How do I eliminate this scenario?

Unfortunately, the only right answer to "How do I eliminate this scenario" is "fix your algorithm."  Yes, you could implement the 3-fold repetition rule, but you should also figure out what it tells you about your algorithm.

This sort of repetition happens when there is an oscillating pattern that arises in your scoring.  Think of it like rock paper scissors.  White makes move to try to achieve a rock position, so black tries to make a counter-move that turns it into a paper position.  Then white tries to create a scissors position and black replies by creating a rock position.

The only way to fix this is to look at your algorithm, and make the algorithm better.  My advice is to put your chess program into a debug mode and have it dump out an analysis of what it is "thinking" with each move.  Look at the factors which lead up to your final score, and understand how they're acting.

Once you understand why the algorithm is doing what it's doing, you can fix it.  Look at the game and decide what move you'd rather see them do, and why you like that move.  See if you can add additional scoring which encourages the type of play you want to see.

One thing in particular I've seen that can cause this sort of behavior is a discontinuity on the horizon.  If your scoring stops at your ply limit, and that position looks good from black's perspective, looking one ply further may show a good position for white instead!  This, of course, will always happen in real life, but you can try to minimize how often it happens by doing a better job of scoring each position.

If all else fails, a little randomness can help nudge the game along.  One mode I implemented when I had to write one of these programs was a variable depth algorithm.  Sometimes it would look at 100,000 positions before making a decision, other times it might make 200,000.  That decreased the probability that I would run into a simple issue just past my horizon, because my horizon kept moving.  Instead, I might blunder into the bad move, but at least the game moved forward!


Obtaining the correct move from syzygy tablebases (Python) I have created a chess engine in Python and now want to start using the endgame tables in syzygy. I have downloaded all the relevant files and is now ready to start.
I have found how to access the files in Python via e.g. the Python Chess module (link). It there explains how I can get the WDL and DTZ information from a FEN position, which could be handy at times. BUT what I really want is to know the move to make to win in that FEN position, and I have not been able to figure out how to obtain this information from the files. The information online is very limited and I hope someone can please guide me on how to do this?

I can't be absolutely certain, as these particular tablebases are unfamiliar to me.  However, in all other tablebases that I've used, from the Thompson and forward, you had, basically, to:

generate all legal moves from the position,
for each move, make the move and look up the score for the resulting position, and then
select 'the right move' based on those retrieved scores, compared to the score for the starting position.


Why is the algebraic notation not just two numbers? Instead of 'a1', why not '11'? First file, first rank.

Instead of 'g6', why not '76'? Seventh file, sixth rank.

And so on. Why not just use two numbers to represent the square, as opposed to 1 letter and 1 number?

I think the notation with the letter is more confusing for beginners and children. For example, with the 'g6'-square, it's not immediately obvious to a complete beginner where the 'g'-file is. They usually have to look down on the letter on the chess board, or, if the board doesn't have letters, they will usually count in their head, from left to right: 'a ... b.. c.. d.. e ... f... g, aha there it is'. On the other hand, if the 'g'-file was simply the '7'-file, it's immediately obvious where it is, since it's much easier to simply find the 7th file by eye-sight.

I believe that it is more of a historic thing where chess players went from descriptive to algebraic notation, really because strong players started adopting algebraic notation. Admittedly, using 2 numbers would probably be just as easy to use once you get use to it.
Infact, ICCF(international correspondence chess federation) uses such coordinate systems in order not to confuse people from different countries who would use different alphabets for algebraic notation.


Chess tactics #4: Black to play and win After the last problem which was very hard I'm bringing you another one which is easier than the previous one. The position is:

[fen "K4R2/RQ4B1/2n5/3q2p1/4PP1p/3p4/pp6/1kr5 w - - 0 1"]

White has just played Qg2 and it's going to lose very quickly. What is the winning move for Black in this position?

This problem is taken again from the Chess Tactics Server.

White threatens mate on g7, but

   1. ... Ne1 pins the queen (and threatens Rf1#; Qxe4 won't stop that) 2. Rxe1 Qxe1+ 3. Qg1 Rf1 wins the queen

and the remaining endgame is easily won for Black.


Where can I play against specific openings? Is there a website where you can play against real people with an opening already installed by default? For example, I want to play against the English opening, but my opponents rarely play it, so I want to practice somewhere.

Lichess also has several thematic tournaments throughout the week.
As an example take a look at this thematic Italian game arena tournament:

When you open the tournament, the opening is mentioned in the upper left corner if there is one:

It is a link so you can click it to see the mentioned opening.
Alternatively you can create your own tournament with a opening of your choice. For that just go to the create tournament area and set the starting position:

In that box you have to place a FEN string. For the English opening considering only 1 C4, you can use the following fen:
rnbqkbnr/pppppppp/8/8/2P5/8/PP1PPPPP/RNBQKBNR b KQkq - 0 1
Regardless you can create any fen of your choice with the lichess analysis board tool or the opening explorer


Why is this move into a simple forced mate annotated dubious and not a blunder? In a recent game against a weak computer opponent on lichess, I (white) was in the following position:
[FEN "Q4k1r/p1Nbbppp/1pn1p3/8/5B2/5N2/P1K1nPPP/R6R b - - 0 1"]

The AI played the move Nb8 giving white a forced mate in 3, annotated by the lichess analysis board as a Nb8?! -- it looks like Bd8 is a better move by blocking the check with a supported bishop.
However, at least to my novice understanding, a move into a forced checkmate (let alone a relatively easy-to-see one in three moves) instead of a far better alternative should be a blunder, not a dubious move (which I understand as "questionable but possibly having merits"). Is there something I'm missing about the nature of this checkmate which makes Nb8 dubious but "possibly having merits", or is it a case of wrong automated annotation?

A blunder is a game-changing move. Nb8 does not change the result of the game which is utterly and completely lost regardless of black's move. Earlier in the game black did blunder when it gave away its queen.
The reason for the "!" part of the "?!" (dubious move) notation in this case is because moving the knight opens up the line of sight of the d7 bishop.


What rules are known for Chaturanga? In the ancient Indian game Chaturanga, what rules are known, and how does it vary from modern chess? Also, is it a solved game?

The exact rules aren't known, but what is known or commonly believed to be true is listed on Wikipedia. Especially the elephant/gaja's movement rules are uncertain.
It varies from modern chess because it has some pieces which move differently: the elephant mentioned above and the mantri/minister. Modern chess has the bishop and queen in their places. Still, the complexity of the game is comparable to chess, so it's a long way from being solved.


Features for evaluation a position I am programming a (relatively basic) chess engine: while it is a lot of fun, it is also an interesting way to improve my chess skills! In order to evaluate a position, I need to extract features from the board. At the moment, I am using basic features such as the total value of the pieces, some features associated to piece mobility, open rank/files, whether the king is castled, some features related to the position of the pieces (eg. occupying the center is good), etc...
I was wondering whether there were resources describing more comprehensive list of features that would likely to be useful. This line of approaches has indeed been done a thousand of times (before the advent of neural-net / convolutional / AlphaZero types of methods) but I have not found many articles describing the features used.

The best way is read source code yourself. https://github.com/official-stockfish/Stockfish/blob/master/src/evaluate.cpp has the commented state-of-the-art rules defined in Stockfish.


Can the King be attacked by a pinned piece? A computer chess game does not permit moving the white King to d2 presumably because it's attacked by the black Knight which I suspect is correct, but the Knight can't actually attack that square because that would put it's King in check.

So, is the game correct?  Is Kd2 illegal?

[FEN "8/8/4k3/8/4n3/8/8/3KQ3 w - - 0 5"]

Kd2 is indeed illegal. You can think of it this way: normally Black can't move his knight because White would "capture his king", but if White were able to play Kd2 then Black would capture White's king before White got a chance to capture his.


Engine is evaluating the same position at the same depth with different score My engine is evaluating the same position at the same depth with a different score inside the search tree, is that normal?

[Title "depth 1   ply 3 alfa -20 beta -15  score -15 (1.Na3 a5 2.Nh3)"]
[FEN "rnbqkbnr/1ppppppp/8/p7/8/N6N/PPPPPPPP/R1BQKB1R w KQkq - 0 1"]

    [Title "depth 1   ply 3 alfa -20 beta -5  score -5 (1.Nh3 a5 2.Na3)"]
[FEN "rnbqkbnr/1ppppppp/8/p7/8/N6N/PPPPPPPP/R1BQKB1R w KQkq - 0 1"]

Search code:

        tab.makeMove(mov);
        // first  time eval value is -15 with alpha -30 beta -15
        // second time eval value is -25 with alpha -30 beta -25
        // this is in the same search
        int eval = -negaMax(depth - 1, -beta, -alfa, ply + 1);
        tab.takeBack(mov);

        if (eval >= beta) {
            return beta;
        }

engine output:

go
info depth 1 score cp 50 pv b1c3
info depth 2 score cp 0 pv b1c3 b8c6
info depth 3 score cp 50 pv b1c3 b8c6 g1f3
info depth 4 score cp 0 pv b1c3 b8c6 g1f3 g8f6
info depth 5 score cp 40 pv b1c3 b8c6 d2d4 g8f6 g1f3
info depth 6 score cp 0 pv b1c3 d7d5 d2d4 b8c6 g1f3 g8f6
info depth 7 score cp 35 pv e2e4 b8c6 g1f3 g8f6 e4e5 f6e4 b1c3
bestmove e2e4

What you are seeing does not necessarily indicate a bug.
You are searching the position with two different bounds.  Your engine is fail-hard (because you return beta and not eval in the case of a fail-high), so the score that comes back from eval is going to be constrained within the bounds you provide.
In the second case (using the numbers from your diagram, not your code) you are searching with a bounds of [-20, -5] and your score is -5.  This is fine.
In the first case you are searching with a bounds of [-20, -15] and your score is -15.  This is also fine.  It would be impossible for this search to return a value of -5 because it is outside the bounds you provided.
In either case, what the search is telling you is that this position is better (relative to the side to move) than the bounds you provided because in both cases the search is failing high.


A possibility that jumps to mind instantly is 26..Qg4, with two threats:

Qxg3+
Re2 followed by either Rxf2 or Bxf2+.

The only move that prevents both these threats is 27.Kf1, but then black could e.g. play Qh3+ or Rd8. Both moves lead to an easy win.
In the position you obtained the most important thing is to make sure white can not solve a threat by developing a piece. As long as you keep that in mind and keep finding new threats and ways to use your pieces to their potential, you should be fine.


When to push centrals pawns? Lets consider you have e4 d4 pawns with white or e5,d5 with black. When your opponent challenge your center with e5 or d5 with black, or with e4 or d4 with white of course his pawns are protected. How do you know if you have to push your pawn or simply capture the challenger pawn?

There are basically three possibilities:

Keeping the tension is often the best one: If your opponent resolves the tension by taking your pawn you can retake and centralise a piece and your remaining pawn often gives you a space advantage.
Taking is usually the least attractive option, but it can be good, if you are the first (or only one) to take advantage of vulnerable squares. So you might take on e5 if you can bring a knight to d5, possibly because the black c-pawn is already on c5, whereas your c-pawn can still control d4.
Pushing the pawn gives you a space advantage, but there is a big difference on which side of the board you get this space advantage! Pushing e5 gives you a space advantage on the king side. This can lead to an (piece-) attack against the king and is therefore a generally attractive option. It is not by random chance that against the French and against the Caro-Kann the e-pawn is often pushed to e5.
Pushing d5 gives you an advantage on the queenside and this is only attractive if you can follow it up with play on this side of the board. Therefore it is generally more often played if you already have a pawn on c4, which is ready to be pushed to c5. If you need too much time to get your queenside play going, there will be the counter lever f5, which gives black play on the kingside.


What professional game has the quickest sequence, starting from move one, to quadrupled pawns? In the blog "AJEDREZ, SIN DUDA", I came across a page that gives a game featuring quadrupled pawns.
[Title "Zheliandinov-T. Sereteli, 35th Championship of the USSR, Kharkov, 1967"]
[FEN "2r1kbr1/pp3pqp/5p2/3N1p2/5p2/6P1/PPn1BR1P/R2Q2K1 w - - 0 1"]

It occurred to me that this game might have the shortest sequence, starting from move one in a professional chess game, to quadrupled pawns. It happens here in just 18 moves.
I have three points of focus.

Is this the shortest such game that satisfies my requirements?
I cannot find the score for the mentioned game. If you can find it, please link it and put it into the replayer.
Is there a way to easily find collections of quadrupled pawn games online?

Regarding your last question:

Is there a way to easily find collections of quadrupled pawn games online?

No need to look online, you can do this on your own.
I've found 3 additional examples after parsing through roughly 300000 games of a TWIC DB:
1)
 [fen ""]
 [Event "FSIM May"]
 [Site "Budapest HUN"]
 [Date "1996.05.13"]
 [Round "11"]
 [White "Lochte, T."]
 [Black "Gross, S."]
 [Result "0-1"]
 [WhiteElo "2220"]
 [BlackElo "2290"]
 [PlyCount "54"]
 [EventDate "1996.??.??"]
 [SourceDate "2011.01.01"]
 [StartPly "54"]

 1. e4 c5 2. d4 cxd4 3. c3 dxc3 4. Nxc3 d6 5. Bc4 Nc6 6. Nf3 e6 7. O-O Bd7 8. Bf4 Qb8 9. Nb5 Ne5 10. Nxe5 dxe5 11. Bg3 Nf6 12. Qe2 a6 13. Nd4 Bd6 14. Rad1 Bc7 15. Nf3 Bc6 16. Bh4 h6 17. Bxf6 gxf6 18. Nh4 h5 19. Qf3 Bd8 20. Qg3 Qc7 21. Qg7 Rf8 22. f4 exf4 23. Rfe1 Qe5 24. Bd5 Qg5 25. Bxc6+ bxc6 26. Nf5 Bb6+ 27. Kh1 exf5 0-1

 [fen ""]
 [Event "8th World Seniors"]
 [Site "Grieskirchen GER"]
 [Date "1998.11.09"]
 [Round "2"]
 [White "Wegener, H."]
 [Black "Knebel, W."]
 [Result "0-1"]
 [ECO "B95"]
 [WhiteElo "2115"]
 [PlyCount "54"]
 [EventDate "1998.??.??"]
 [SourceDate "2011.01.01"]
 [StartPly "48"]

 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6 7. Bd3 Be7 8. O-O b5 9. a4 b4 10. Na2 a5 11. e5 dxe5 12. Bxf6 gxf6 13. Qf3 Ra7 14. Bb5+ Kf8 15. Nf5 exf5 16. Qe3 Qd4 17. Qh6+ Kg8 18. c3 Qg4 19. Qe3 Rc7 20. cxb4 axb4 21. Rfc1 Rxc1+ 22. Rxc1 Kg7 23. h3 Qg5 24. f4 exf4 25. Qxe7 Be6 26. h4 Qg3 27. b3 f3 0-1

 [fen ""]
 [Event "Open"]
 [Site "Pula CRO"]
 [Date "2001.05.24"]
 [Round "7"]
 [White "Molnar, Be"]
 [Black "Polak, T."]
 [Result "1-0"]
 [ECO "D42"]
 [WhiteElo "2352"]
 [BlackElo "2503"]
 [PlyCount "80"]
 [EventDate "2001.05.18"]
 [SourceDate "2011.01.01"]
 [StartPly "66"]

 1. e4 c6 2. d4 d5 3. exd5 cxd5 4. c4 Nf6 5. Nc3 e6 6. Nf3 Be7 7. cxd5 Nxd5 8. Bd3 Nc6 9. O-O O-O 10. Re1 Bf6 11. Be4 Nce7 12. Qd3 h6 13. Ne5 Nxc3 14. Qxc3 Nf5 15. Be3 a5 16. Rad1 a4 17. Ng4 Bg5 18. Bxf5 exf5 19. Bxg5 hxg5 20. Ne5 Qa5 21. Qc4 Be6 22. d5 Rac8 23. b4 axb3 24. Qxb3 Rc5 25. Ng6 Rc3 26. Qxb7 Rc7 27. Qb1 fxg6 28. Rxe6 Kh7 29. d6 Rd7 30. Qb3 Rfd8 31. g4 Qc5 32. Qd5 Qxd5 33. Rxd5 fxg4 34. a4 Ra8 35. Re7 Rdd8 36. a5 Ra6 37. d7 Ra7 38. Kg2 Raa8 39. Rxg5 Ra7 40. Rd5 Raa8 1-0

Briefly, how I've done it in Python and using python-chess to read the PGN DB:
I scan through each game of the DB mapping each position to its FEN, then I expand the FEN by replacing numbers with a corresponding amount of dashes '-'. In the FEN notation numbers in between the rank '/'-separated sections denote how many empty squares there are before a piece reached on a given row) so e.g., this FEN
'3r4/3PR1pk/r5p1/P2R2p1/6p1/8/5P1P/6K1'

becomes:
'---r----/---PR-pk/r-----p-/P--R--p-/------p-/--------/-----P-P/------K-'

which you can easily do as follows:
(after removing everything after the first space fen=fen[0:fen.index(' ')])
def isinteger(s):
    try:
        int(s)
        return True
    except ValueError:
        return False

for el in fen:
        if isinteger(el):
            fen = fen.replace(el,int(el)*'-')

Then we know we want to find consecutive rows having pawns (of same color) on the same files, so if you split the FEN string
according to the '/' separators into a list (splitfen = fen.split('/')), you have to match the pattern that letter 'p' (denoting black pawns in FEN, similarly, 'P' for white) occurs in 4 consecutive elements of the list and at the same position of the strings of size 8 (to ensure they're on same file) which you can go about in many different way:
#(the function that finds all consecutively matching patterns for t)
def checkpattern(sp,t):
    start = [sp[0]]
    for i in sp[1:]:
        if any(all(t == c for c in b) for b in zip(*(start+[i]))):
            start.append(i)
        else:
            if len(start) > 1:
                yield start
            start = [i]
    return

splitfen = fen.split('/')

forblack = list(checkpattern(splitfen,'p'))
forwhite = list(checkpattern(splitfen,'P'))
total = forblack+forwhite
  for el in total:
    if len(el)==4: #(since we want quadrupled pawns)
      res = True
      break

All such kinds of search queries across chess DB's can be easily performed with a bit of scripting around the FEN to spot the wanted patterns (be they pawn structures, number of pieces etc).


Why don't we play different openings in chess? Chess comes in many forms, both with respect to the clock and the board format.

But why don't we have chess tournaments where we play different openings? That is, a certain list of openings is picked (it could be publically announced prior to the tournament, or perhaps a surprise reveal), and then both players play games with those openings (each opening is played twice, once as black, once as white).

This seems like quite a fun thing to do and an obvious extension to the many forms of chess we already have?

What's the drawback?

There are thematic tournaments.  For example, I recall a GM tournament where they had to play an open Sicilian.


Substituting one engine for another in a tournament I am running a strong computer chess engine tournament, using arena 3.5.1 All engines are playing a large number of games. One engine appears to be glitching so I want to replace it with another alternative (in terms of CPU speed / compatibility) of the same version of the engine.

Is it possible to substitute one engine with another and retain the points that the other engine has already earned?

You can delete the old engine executable and copy a new one with the same filename to the same directory.


Why does white exchange knight for a pawn here? This other question asks about why white resigns at the end (Why did Polgar resign?), but running through the game, I am confused at move 49 where the board looks like this, white to move:

Polgar-Kasparov:

8/8/1k6/p6p/3n3r/PNR5/6K1/8 w KQ - 49 50

The next move is white to take the pawn with her knight, and have the knight taken by the king.  Since the knight would be lost, why not take the black knight instead?

After taking:

8/8/1k6/p6p/3r4/P1R5/6K1/8 w KQ - 49 50

Judith Polgar must have assessed this position to be easily winning for black. I assume black would just win the white pawn and proceed to promote the a-pawn.

Now, while a knight is generally worth much more than a pawn, the endgame King,Rook,Knight vs King,Rook is usually a draw. So Polgar must have hoped to win or blockade the h-pawn and reach a drawn endgame of the K,R,N vs K,R-variety. I guess she knew this wouldn't work out, but the rationale was to set a more difficult technical task to Kasparov than the above rook endgame.

Edit: I looked up the game in her autobiographical best games collection and it turns out, I was half right:

"Following the text move, the rook ending after 50.Nxd4 Rxd4 would be lost for me. Black would advance his pawns to my fourth rank and then activate his king using the rook as shield."

She then proceeds to give 50.Nxa5 an exclamation mark, explaining that it is a study-like way to a draw, because apparently she wins the black pawn by force (which I didn't see).

So, she did assume the rook ending to be lost (erroneously, according to Stephen's comment), but she actually saw that she would win the h-pawn as well, leading to a drawn endgame.


Why do professional chess players point at the pieces with a middle finger? I've recently heard and then actually started to notice more and more that professional chess players tend to use a middle finger when pointing at pieces on the board like in this Anand vs Caruana game during the Sinquefield Cup 2017:

(source)

I am wondering, why is it happening?

Note: this is a genuine question, I am not trying to offend or make fun of anything or anyone here.

When they're analyzing at a rapid pace, they tend to only need the thumb and index finger to pick up pieces and move them. Using the middle finger as well doesn't really help. So since that finger is freed up, they can use it to point (especially because pointing with the 4th finger or pinkie is awkward).

Or they subconsciously despise each other.


Getting better at OTB chess I live in a small town where there had been a total of 2 tournaments during last 5 years and 0 chess clubs, hence I have almost nil experience playing OTB chess. But sometimes I set up a board and play with my family. I have noticed that I miss a lot of tactics and obvious mates which I couldn't have missed while playing on Lichess. Also, I can't calculate properly OTB. I am shifting to the national capital this year where hopefully I would get to participate in OTB tournaments.

Is it a normal problem for those who play predominately online chess? How do I go about improving my OTB play?

One suggestion I have seen for how to improve learning when studying openings and tactics is to involve the other senses. This involves not just using sight, looking at the position on a computer, but also setting up the position on the board and playing through it (touch) and (for openings) saying the moves out loud (hearing) as you play them.

I was a bit sceptical when I read this but your experience backs this up. The obvious way to address this problem is to follow the advice and set up tactics problems on a real board so you practice "over the board".


Why can't I castle on Arena chess? I play chess a lot against Arena (the GUI thing),
but I can't seem to castle.
The requirements for castling are met, just the castling itself doesn't work.
I'm on windows.

For the record (adapted from my comment above): as with other such interfaces, if you move the King to its target square, the corresponding Rook will automagically land on the right square to complete the Castling.  (A move like Ke1-g1 or Ke8-c8 can only mean Castling.  Usually the computer will refuse the move if Castling is illegal for some reason.)


How do you use 'en passant'? I have been playing chess for years but I was just introduced en passant only recently. I keep on forgetting when to play this weird move. I keep on asking myself "is it on the 5th row or the 4th row" If there is an easy way to remember, please help.

Perhaps it helps if you remember the (presumed) reason for having this special move.

Originally pawns were only allowed to make single steps. This meant that pawns on adjacent files could not pass each other without running into the danger of being captured.

When the double step was introduced, pawns on adjacent files could suddenly pass each other (which would have changed the evaluation of many positions most notably in endgames). They could pass each other exactly in one case: white pawn on 5th row black pawn making double step (or equivalently black pawn on 4th row white pawn making double step).

So bottom line if you see a pawn passing your pawn without your pawn ever having a chance to capture it, it is time for en passant.


Problem: reconstruct the game In the following position, each side has made exactly 4 moves (8 in total).

[fen "rnbqkbnr/pp3ppp/2p1p3/8/4P3/8/PPPP1PPP/RNBQK1NR w KQkq - 0 1"]

I need to find what these moves were.

Dag Oskar Madsen's (quite generous) hint:

  The last move was king takes e-eight.

And here's the full solution:

  Pawn to e-four, pawn to e-six, bishop to b-five, king to e-seven, bishop takes d-seven, pawn to c-six, bishop to e-eight, king takes e-eight.

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

1. e4 e6 2. Bb5 Ke7 3. Bxd7 c6 4. Be8 Kxe8


Why is chess dominated by relatively young players? The top FIDE rated players (2700 chess) are all under 50 years old. Most of them seem to be around the 23-32 age range. Why is this the case? I don't really know if this has always been the case or if it this is just something apparent in the current generation.

I'm guessing this is the case for a number of reasons that may include:

Leaving chess
Lacking needed attention
Lacking stamina
Impaired memory of positions and theory

Well, all you mentioned are probably the reasons for some players.

I would also add 'lack of time' as one of the reasons. When you get older you may need to go to a college/university (chess don't bring much money, unless you are at the top), then family life/kids (chess players have to travel regularly a lot) makes travel harder... So, many people 'switch' to teaching and playing only in local tournaments.


What is the Elo rating of Stockfish version that played AlphaZero? AlphaZero has defeated Stockfish with all novelties and brilliant strategic sacrifices. But some people were disputing its win, because Stockfish was running on weak hardware (1 GB RAM), not access to opening book, not having free time control, maybe not have endgame table base, etc.
This setting by DeepMind is understandable from a scientific perspective though. It is to test intuitive/strategic play by deep learning technique vs. counting/tactical play by brute force search. However, this leaves chess lovers with many questions like what is the true strength of AlphaZero? What is the true advantage of strategic/positional sacrifice play? Were Morphy, Tal, and others correct and Stockfish wrong? Or full version Stockfish is still the best?
One work around is to replicate the Stockfish version that played AlphaZero, to see how strong it is compared to the full version and other engine and human. Thus we could infer the Elo rating of AlphaZero and answer most questions.
So, did anyone test it? Is anyone interested in testing it? Maybe Stockfish developers, because Stockfish's pride is at stake? Or is there other way to approach the problem?
Thanks
Edit:

Note that Stockfish had good 64 threads CPU and could evaluate 70 million positions/second.
The Stockfish Elo rating provided in the paper is the full version, thus this replication is needed.
The paper.

The Stockfish version that played agaist AlphaZero was significantly compromised in several different aspects:

There was no opening book available
Time control was 1 minute/move, which throws out of the window various optimizations re: using more time thinking about difficult moves
Stockfish had threads=64 set, but the actual hardware had only 8 CPU cores, that effectively slowed things down quite a lot
The hardware was quite different -- an average $1k PC (Stockfish) against a bunch of specialized hardware that might cost millions and is not accessible to anyone
There are more, but these are main points.

Answering your question, there's no way to measure how much rating Stockfish had in a very handicapped conditions it had to run.

Nonetheless, winning over Stockfish is quite an achievement, no matter how handicapped it was and how much was the difference in hardware cost.

UPDATE: in the recent article "AlphaZero: Shedding new light on the grand games of chess, shogi and Go" the rating for Stockfish was drawn as a line at 3500. Besides that, the article provides the new games played with a reasonable time control for SF as well as opening books.


Online personalized database resource I'm searching for the possibility of having my personal database of annotated games in the cloud, my games included. I already read this post: 1) http://chessmicrobase.com/ looks nice, although basic, I already added a game, but the problems are that I cannot I add variants and I'm not very sure for how much time this site will be reliable. 2) http://www.chessgames.com/ is slow and ugly (java based) and I cannot add my own games, premium membership included. But the main problem is that is very slow.

I'll be happy also with a simple cross-platform chess edit application, with the same features and the possibility to integrate chess engines, but my main interest is in the online.

Chess Microbase is the only thing I found.

You can have 3 databases for free which is probably enough in most cases.
You can also share the link to the game.
Supports importing and exporting with PGN.
Has support for annotations.
I am using it for couple of years now (I think). It seems reliable and seem to get new features. Of course, take backups.


One board tournament I work at a public library and we used to offer a monthly chess night, which is on hold right now due to lockdown regulations. We are planning to offer a small garden chess tournament outside the library with one chess set and maybe pre-registration to control crowd size.

What would you say is a good time format to offer? What tournament mode?

I was thinking to just do some "winner stays at the board, 6 challenges 15+0" kind of thing?

That'd probably be the best way- yes. A typical tournament would be difficult. Probably a blitz time control (something like 3+2) would be best, so games are over quickly. You'd also have to consider what'd happen if a draw occurs- my suggestion is to let the guy who won the game before that stay, or play another game. Also colours have to be decided- id say flipping a coin'd be best (other random selection alternatives are also good).


How did Taimanov lose this game to Karpov? I can't understand how Taimanov (playing White) resigned in the following position against Karpov from the Moscow team leagues in 1973:

After 40.Rc2 or 40.d5 the position seems to be equal. I know Taimanov was notorious for getting into time trouble. Did he just forfeit on time?

In the book "How Karpov Wins" by Edmar Mednis it is stated on page 174 that "White overstepped the time limit and lost". The book seems to be fully available on Google books and has a lot more analysis of the match.

https://books.google.com.au/books?id=x8MV0uoAJp0C


Lichess' Stockfish's tuning I remark that whatever the level of the Lichess' Stockfish I choose it plays in average at the same speed. How could I tune my Stockfish (the one I use in Fritz or Arena) to achieve the same with the same performance ?

The settings used for the Stockfish levels on lichess can be found at https://github.com/niklasf/fishnet/blob/53e218bd184554265748513f85d19e601f18c310/fishnet.py#L117-L119:

LVL_SKILL = [0, 3, 6, 10, 14, 16, 18, 20]
LVL_MOVETIMES = [50, 100, 150, 200, 300, 400, 500, 1000]
LVL_DEPTHS = [1, 1, 2, 3, 5, 8, 13, 22]

where LVL_SKILL refers to the Skill Level UCI option in Stockfish, LVL_MOVETIMES to the maximum move time in milliseconds, and LVL_DEPTHS to the maximum depth for each of the eight levels.

The move time and depth might not be easy to set in a local GUI, but you can simply use the Skill Level option to adjust playing strength where 20 means best play and 0 is the lowest available level for Stockfish.


Commented games for beginners I'm looking for a website where we can find annotated games for beginners. I mean games with basic comments and lenght of the game is short.
The best would be that we can see the pieces moving but kind of optional.

YouTube is a good resource to consider.  There is one user in particular that annotates miniatures rather well for beginners, and as a bonus, he sounds like Dracula.

https://www.youtube.com/user/MatoJelic


How many times can the king and its surrounding squares be attacked? In a legal position, how many times can the king and its surrounding squares be attacked? There is a total of 9 possible squares to be attacked-the square the king is on and the eight squares surrounding it. The final tally is the added total of the number of times each of the nine squares is attacked.

Adding on to @Brian Tower's answer as anticipated, here is an improved position with 55 attacks, using double check and White's full arsenal. Black last moved a piece to e7 that White's rook captured with checkmate.
[FEN "B7/4R3/3Q1Q2/2Q3Q1/2N1k1K1/1R4Q1/1BNQNQN1/8 w - - 0 1"]

However, it is also possible for both sides to attack under the OP's loose ruleset. I have found a lower bound of 83 attacks by White and Black, with eight of them coming from the Black king itself.
[FEN "8/3Nnn2/1bnQqQb1/1r4Q1/1nq1k1qN/1R4Q1/1BNQqQB1/2K1Nn2 w - - 0 1"]

If you are wondering of all of those pawns really could have promoted, I present evidence that it is possible.
[FEN ""]

1. a4 b5 2. h4 g5 3. c4 d5 4. f4 e5 5. cxd5 bxa4 6. fxe5 g4 7. Rh3 gxh3 8. h5 Nf6 9. h6 Rg8 10. e6 Rg7 11. hxg7

Finally, just for fun, here is 88 attacks by one side in an illegal position. Any piece can be color swapped to produce a result for both sides.
[FEN "8/2NNNNN1/1NNQQQNN/1NQ3QN/1NQ1K1QN/1NQ3QN/1NNQQQNN/2NNNNN1 w - - 0 1"]


In the Dutch Defense, why does white play b3 and Ba3? In the Stonewall Dutch Defense, why does white play b3 and Ba3? Should I try to avoid it, or does it not matter?

[fen ""]

1. Nf3 e6 2. d4 f5 3. g3 Nf6 4. Bg2 d5 5. O-O Bd6 6. b3 O-O 7. c4 c6 8. Ba3

The main reason is to exchange black's good bishop, and what would probably end up being white's bad bishop after a later e3. Another common way of doing this is Bg5xNf6. This also highlights black's dark-square weakness problem that he will have to watch out for for quite a while.

This exchange on a3 leaves black's other bad bishop on c8 more markedly bad, and the e5 square more weakened. After the exchange on a3, black can, and usually should, gain a tempo with Qe7, and the white Na3 will redirect to Nc2-e1-d4 (or sometimes via Nc2-b4-d3) to further control e5.

This scores well in my database at 67% for white, but many of the games are between players of disparate ratings. At the higher levels, it seems that black can hold equality, so I would say that if you are stronger, there is no need to avoid it, but if you are weaker against a good positional player, you might want to try to get in Qe7 earlier to make Ba3 harder, but white still has a4 then. I am not sure you can really, and totally avoid it if that is the plan white chooses.


Why does FIDE rate women in different category? Has FIDE ever given reasons why it rates woman in different category and organises their tournaments seperately?

First, let's clear up a misunderstanding.  Women and men are rated on the same scale, with the same formula.  A woman with a FIDE rating of 2400 can be assumed to be equally matched with a man with the same 2400 rating.  FIDE merely defines four titles that are only available for women.  In general, woman can and do participate in tournaments against men.  However, there are a handful of tournaments open only to women, including a Women's World Championship.

The reason for the tournaments and titles is obvious: some women want to participate in such tournaments, and some women appreciate the titles.  Chess is filled with reserved tournaments and not-too-prestigious titles of other kinds - this isn't a "woman-thing".  Every club, state, or national championship is a tournament which sacrifices strength and prestige to encourage the participation of a specific group.  The USCF has titles down to "4th Category", a title which requires hardly more than a heartbeat and a willingness to play in at least five tournaments, obviously to encourage tournament play among those still learning the game.  FIDE correctly calculates that having the WGM, WIM, WFM, and WCM provides motivation for some women and encourages them to improve their game and participate in tournaments.  Given that FIDE exists to promote chess among all populations, including women, providing these title is a no-brainer.

Damning women who participate in such tournaments or accept such titles is as ridiculous as complaining that the Canadian National Championship is tainted by the lack of Americans in the field or considering the USCF Candidate Master title to be a farce because it is easier to obtain than the FIDE Candidate Master.  There is no shame or fraud in competing for these titles, as the requirements are well-known and observers can easily understand exactly how much prestige should be attached to them.  Some of the strongest women players may disdain the women-only titles, but there are many male GMs who disdained their IM or FM norms.  You may choose to learn what you want from their examples.


Windows chess program that can load PGN files per command line the program should display a PGN file, be fast to run, and absolutely be expected to be callable by the command line (passing the PGN file as an argument).
The reason is I began to create a concept map about an opening, and I can call from this map some EXE programs. I would like to display some games as examples of the nodes.

I already searched, but till now I found nothing.

There are at least two Windows programs that you can start per command line: Arena and SCID (or SCID vs PC).

Arena

To open a PGN file in Arena, call it with:

Arena.exe -loadgamefile "path/to/sample.pgn"

There are many more options listed in the help file under Miscellaneous/Command Line Parameters. analyze is particular useful.

SCID and SCIDvsPC

Both come with the same very small set of command line options. Again see the help file.

Open a PGN file with:

scid.exe "path/to/sample.pgn"

Arena's command line support is far superior in my opinion.


Why is capturing the bishop in this position a blunder? [FEN "r2n1rk1/pp1bppbp/1n4p1/q1N5/3P3N/PB2B2P/1P3PP1/R2Q1RK1 w - - 3 18"]

Why is Nxd7 a blunder in this position?
I think that once the light squared bishop comes to c6 it will become very strong and hence removing it should be a good move, but according to Stockfish after Nxd7 the evaluation drops from around +4 to +0.6.

It is a blunder White can win a piece instead. Black's queen is trapped in a molasses of its own pieces, so to speak, and White has a very good chance of trapping it. Capturing the bishop loses this large possibility, and is thus a grave mistake.
Here is White's best line of play that quickly plants Black a firm loss.
[FEN "r2n1rk1/pp1bppbp/1n4p1/q1N5/3P3N/PB2B2P/1P3PP1/R2Q1RK1 w - - 0 1"]

1. a4 Qb4 2. a5

By playing a4, White threatens to play Bd2 on the next move, winning the Black queen. Moving the Black knight on b6 to clear room for the queen doesn't help. This is because moving it will lose the bishop on d7, which is attacked by the White knight on c5. As such, Black's best move is Qb4. Now White can play a5 and win a piece! Either the Black knight is taken by the pawn, or it moves, and the bishop is lost.
In other words, playing Nxd7 is a blunder because the chance to win a piece, and likely the game as a result, is lost. This teaches that it is very important to look out for any threats that you can make.


Comment/variation with different starting position When annotating games, I sometimes want to add a comment which starts from a position that is different from the current position.
Like:

1. d4 d5 2.c4 { Our previous game went 1.e4 c5 ...}

Or:

25. Bf3 { Here I remembered a similar position from a famous game: <some fen notation>}

When writing/printing this is no problem. But when I want to generate playable pgn for a website, this doesn't work.

Attempting this in pgn would look something like:

>[White "Game 1"]
>[Black "?"]
>[Result "*"]
>1. d4 d5 2. c4 (1. e4 c5) *

>[White "Game 2"]
>[Black "?"]
>[Result "*"]
>1. e4 c5 2. Nf3 ([FEN "rnbqkbnr/ppp2ppp/8/4P3/2Pp4/5N2/PP2PPPP/RNBQKB1R b KQkq - 0 4"] 4... Nc6 5. a3 Nge7 ) *

However, this format is not accepted by my chess program (Chessbase) and also not according to the PGN standard.

Does the PGN standard support something this?

What should I do in order to manage to generate playable pgn for a website?

You can't do this in PGN, not the way you want it.

There are some tricks that publishers (especially Everyman) use to create their "PGN ebooks":

They split the book over many different PGN games. You'd say "Here I remembered an earlier game that had a similar position; see X vs Y after this game."
A variation that starts at move 1 has to start at move 1: 1.d4 ({Our previous game went} 1.e4 c5) 1... d5
Null moves can be added as --, to show threats and such: 1.e4 e5 2.Qh5 Nc6 3.Bc4 ({With the subtle threat} 3... -- 4.Qxf7#)
You can have several variatiations all starting with the same move, or all with the null move, as poor man's paragraphs.
If all else fails, just leave it as text. People still buy paper books so it can't be that bad...

Note that the variations I had, with a comment starting before the first move of a variation, may be something that not all software supports; I'm not sure. It used to be possible to enter comments like that with older versions of Scid but newer versions make it hard to get to the point where you are still in a variation, but before its first move. I think it's legal PGN though.


When to give up on winning a game e.g. due to material In what situations is it impossible to win for a player?
For example due to not enough material or the composition of the material is not useful.
I guess for example when you only have a king and a knight left or so and the opponent has far more pieces?
I'm looking for the (few) hard cases where "you can't win". For example when you only have a king.

There are very few positions in which it is actually impossible to win although you are up material. Basically only KN vs K or KB vs K.

Then there are positions which can be won, but this would require such egregious errors by your opponent, that in practice a draw will inevitably be agreed. Examples are KNN vs K, KBB vs KB, KR vs KB.

And then there are theoretically drawn positions which give you very real winning chances even against strong players. KR vs KN, KRB vs KR, KQ vs KNN.

There are also known "fortresses" where the stronger side cannot break through once the weaker side has achieved a certain setup. Here is one famous (and relevant) example:

   [White "The wrong"]
   [Black "bishop"]
   [FEN "k7/8/8/PK2B3/8/8/8/8 w kq - 0 13"]


The exsistence of IBM’s Deep Blue How would IBM’s Deep Blue fair against modern day champions like Carlsen? Was it decommissioned after Kasparov's game?

The match with Kasparov was very close - 3.5 - 2.5 and it is arguable that Kasparov's loss was due to psychological factors. Until Carlsen's recent disastrous tournament where he went to pieces psychologically after over stepping the time control in round one I would have said that Carlsen is psychologically stronger than Kasparov but now I'm not so sure.

Modern day players like Carlsen have closed the gap that existed between Kasparov and the rest without opening up a big gap. I want to say that Carlsen would beat Deep Blue but I suspect the truth is that it would be a close match again.

Deep Blue was dismantled and parts of it can now be seen in two different US museums - http://en.m.wikipedia.org/wiki/Deep_Blue_(chess_computer).


Which legal position has the smallest number of moves in a "forced loop"? Consider this (illegal) position.
[FEN "5n1k/3p1p1p/3PpPpP/4P1P1/1p1p4/pPpPp3/P1P1P3/K1N5 w - - 0 1"]

If we do not consider the position's illegality, and the fact that it is clearly unwinnable by eiter player (and therefore an automatic draw even if either of the players resgined, ran out of time, etc), then this position has an interesting property. Regardless of what move every player does (which is obvious in this case, since there is always only one legal move), the position results in forced threefold repetition in 4 moves.
Now here arises a question, basically a problem creation: Which legal position has the least amount of moves to make threefold repetition, assuming no player wants to repeat the positions?

This legal postion should fit the bill for the least amount of units needed and the least amount of moves. There is one king, one bishop, and four pawns for each side-a total 12 pieces. The threefold repetition is forced no matter what moves the players make since they only have one legal move each time. It's basically your idea in a legal and lighter setting.
[FEN "5b1k/4p1p1/4P1P1/8/8/1p1p4/1P1P4/K1B5 w - - 0 1"]


Valid PGN variations? I've received the following PGN text that I suspect invalid:

8.f4
    {0.22/17 0 last book move}
8...e5
    ( 8...b5
       ( 8...Qb6
           ( 8...Qc7 9.a3

What exactly the position the moves come from is unimportant. Please note the PGN text has four 8th Black moves (8...e5, 8...b5, 8...Qb6, 8..Qc7), and two of them (8...Qb6 and 8..Qc7) are under 8..b5.

I suspect this is a mistake because the alternative Black moves should be represented like the diagram:

I generated the diagram with the Scid vs PC software. Please note the alternative Black moves are written in parallel. For example, 8...Qb6 and 8..Qc7 are not included inside the 8...b5 bracket.

Some softwares (e.g. Scid) are able to read it, but some fail (e.g. ChessX). My own PGN implementation can't handle the nested structure.

Q: Is the PGN text I posted valid? What does the PGN specification say?

EDITED:

The game is here. Open the game in a text editor, and you will see the following:

e5
    { 0.22/17 237 }
    ( 8...b5
        ( 8...Qb6
            ( 8...Qc7 9.a3

Good question. This nested notation (also called: recursive annotation variation, RAV for short) is uncommon but valid[*]. In the example you provide, most online PGN readers have no problem parsing and accounting for all the variations and subvariations. So the way to read it is as follows: the nested structure is composed of independent variations, only if there's a closing parenthesis then it is an actual subvariation (so a specific branch out of a previous variation). An example from your PGN: 8... Qc7 is a variation, (9.Qe1...) is a subvariation and (10.Bf3...) is a subsubvariation. So the nesting is: (8... Qc7 (subvariation (subsubvar...) )).

Various libraries/modules may not have a built-in parsing system to tackle such PGN structure[**], so you may have to extend this on your own. For further reading, Tim Harding also explains the nested notation and its lack of implementation rather more succinctly here, I briefly quote:

  An RAV (Recursive Annotation Variation) is a sequence of movetext
  containing one or more moves enclosed in parentheses. An RAV is used
  to represent an alternative variation. The alternate move sequence
  given by an RAV is one that may be legally played by first unplaying
  the move that appears immediately prior to the RAV. Because the RAV is
  a recursive construct, it may be nested. ...

  Some software may find it
  hard to handle nested variations too. Palview3 was the first
  freely-available PGN software, that I am aware of, that could create
  with variations in HTML pages, and it is restricted to two levels of
  notes (three levels counting the actual moves of the game). For most
  purposes, this is sufficient. Most Java Viewers can only show the
  actually played moves, except as text notes, but playing through a
  Palview3 web page is close to the experience of playing it through in
  a program like ChessBase: a major advance for chess webmasters.

That said, nowadays, there are various online pgn-readers that already do this, some examples (so if you paste your PGN onto either of these, it can be fully read and displayed).

https://www.chess.com/analysis-board-editor
https://chesstempo.com/pgn-viewer.html
http://www.apronus.com/chess/wbeditor.php

You may find additional information on the standards of PGN here. I will get back to you if I find other potentially useful elements.

[*]: just to make sure, I also quickly parsed the text to make sure all parentheses are properly closed.

[**]: for example, the chess.pgn.read_game method from python-chess fails to fully read this PGN, it only sees the main variation upto move 8... e5.


Getting started in position-counting by computer I have quite a bit of programming background, and even game programming background, but have never looked at a real chess engine before.

I recently stumbled on this puzzle-question, which asks for the number of four-piece positions where the next move (whosever it is) will be checkmate. The number has to be somewhere between 400 (the count found by the OP) and 381,225,600 (the total count of four-piece positions), so it ought to be easy to enumerate them all by computer.

I'd like to make a quick program like this:

for white_king_pos in [0, 64):
  for black_king_pos in [0, 64):
    for white_piece_pos in [0, 64):
      for black_piece_pos in [0, 64):
        for white_piece_kind in {Q,B,N,R,P}:
          for black_piece_kind in {Q,B,N,R,P}:
            if next_move_wins_for(black) && next_move_wins_for(white):
              count = count + 1

What library should I use in order to make writing the next_move_wins_for function as painless as possible?

(My program is so simple that I don't care about the library's choice of programming language. But FWIW, my fluent languages are C++, Python, and C.)

Edited to add: Same question for other ways of accomplishing the goal, e.g. tablebases. :)

You can do that easily in Python.

  https://pypi.python.org/pypi/python-chess

Create a FEN position based on your loops
Make it white to move in the FEN
Use the FEN position to create Board (http://python-chess.readthedocs.io/en/latest/core.html#board)
Use the legal_moves function to generate all possible moves
Use the push function to make the move
Use the is_game_over function to check for checkmate
Use the pop function to undo the move
Go back to push until you have tried all legal moves
Now make it black to move in the FEN and repeat step three

PS: If you want to add tablebase support. There're two ways:

Use API provided from https://syzygy-tables.info/apidoc?fen=4k3/8/8/8/8/8/8/4K3%20w%20-%20-%200%201.
If you prefer to do it locally, download Syzygy files from http://kirill-kryukov.com/chess/tablebases-online. Use chess.syzygy for probing.


Why doesn't Lichess' Stockfish suggest this bishop sacrifice? I arrived at the following position in an online game after the opponent left a queen hanging.

[FEN "r1b2r2/pp1p1ppk/2n1p3/6B1/2P5/5N2/PQ3PPP/R4RK1 w - - 0 16"]

In the game, I played 16. Bf6 with the idea that in case he accepts the sacrifice, my queen can come to an exposed king with mating ideas and possibility of exchanging the rook for the knight and I should probably be able to arrive with the rooks by lifting them sooner than his minor pieces are able to help significantly. If the opponent refuses, my bishop is still up with a better aim and I have possibilities of blasting the kingside with a major advantage.

I looked at the game with lichess' Stockfish to check if this was a blunder and the main lines lichess' Stockfish suggests to me are 16. Be3, 16. Qc2+, 16. Nd2, 16. c5 and 16. Qa3, the first line having an evaluation of +12.8. Bf6 is not suggested, but it has an evaluation of +18.0 after it is played, so it left me wondering why it doesn't suggest Bf6 in the first place. My guess is that maybe Stockfish does not consider sacrificial moves without a forced advantage if the player has a large lead, which seems reasonable, but this is only a guess.

Running an analysis in chess.com with the Komodo engine suggests Bf6 as the best move, with +11.6 evaluation, so it left me even more curious as to why Stockfish doesn't even consider it.

Good question. I let Stockfish 11 think on the position, and even by around depth 25-26 it didn't suggest Bf6. But like in your case, after making the move on the board, Stockfish suddenly realizes it is the best move. Although what's also odd is that after Bf6 gxf6 Qxf6, it takes Stockfish longer than at least depth 27 to realize it's a mate in 9 moves/18 ply (instead of some evaluation that's "only" over +20).

One possible explanation for all this is due to how engines prune. If an engine spends an equal amount of time examining every single move in its calculations, it will be very slow (there's an average of roughly 30 moves in a given position, so the complexity for searching everything is on the order of 30^depth). Therefore, they will spend more time thinking on moves that look more promising, and stop wasting as many resources on moves that look clearly worse.

In the position you posted, there are multiple moves that give at least a +12 evaluation. Meanwhile, Bf6 drops a bishop, and perhaps it is only multiple moves further that White's overwhelming compensation for it becomes apparent. There are already many +12 moves available from the starting position, so an engine could decide not to waste time going deep into the Bf6 branch, stopping at a point before it realizes how good it is.

But then when you actually play Bf6 on the board, there's nothing else for the engine to look at. It's "forced" to examine the Bf6 branch, and then it quickly realizes it's very good (although in Stockfish's case taking a while to realize it's a forced mate, likely due to this same pruning issue).

Note that all the above is just my own understanding of things, and there could be other factors at play. If I had to guess why Komodo suggested Bf6 to you but not Stockfish, it would be because Stockfish prunes more aggressively in order to be extremely fast in searching.