Why would one promote a pawn to a knight?

White to move:

[FEN "8/q1P1k3/8/8/8/8/6PP/7K w - - 0 1"]

Since my example is rather contrived and artificial, I'll also say that the so-called Lasker trap in the Albin Countergambit gives a more realistic setting, and one where a knight promotion is the best option as early as move 7:

[FEN ""]

1.d4 d5 2.c4 e5 3.dxe5 d4 4.e3 $2 Bb4+ 5.Bd2 dxe3! 6.Bxb4 $4 exf2+ 7.Ke2
fxg1=N+ $1 8.Ke1 Qh4+ 9.Kd2 (9.g3 Qe4+) Nc6 $19

Oddly enough, I happened across that line for the first time just earlier today.

Oh, and there are situations where underpromotion to a bishop or rook is necessary in order to avoid a stalemate that a queen might create. For instance, in the sequence of moves coming from the Saavedra position, if white were to create a queen with 6. c8=Q, this would allow black to draw by stalemate, and so white must instead play 6. c8=R in order to win:

[FEN "8/8/1KP5/3r4/8/8/8/k7 w - - 0 1"]

1.c7 Rd6+ 2.Kb5 Rd5+ 3.Kb4 Rd4+ 4.Kb3 Rd3+ 5.Kc2 $1 Rd4 $1
6.c8=R $1 (6.c8=Q $2 Rc4+ $1 7.Qxc4 $10) 6...Ra4 7.Kb3 $18


I agree that 1.d4 and Queen's gambit are the best option from what you told about yourself.

In French, it's typical to have d4-d5 pawns in the center, a bad black white-squared bishop, space advantage for White and a plan based on c7-c5 for black. These points are also common in the Queen's gambit declined. I write from my own experience of playing these openings.

You might also search through a database and see which grandmaster's style fits you well, and copy their opening repertoire. Good luck!


[fen "2rq2kr/p1ppbp2/1pn1p1pP/4P3/3P2Qn/2P5/PP3P2/RNB1K2R w - - 0 1"]

Is white in a weaker position then black? ... What are the key points?

The key points are -

White is a whole piece down for no compensation
White has no attack
White has no pawn levers
The white h pawn is weak and black can round it up at leisure and take it

In short, white is not just weaker than black, white is completely lost

Please review it again. My bad, I missed the white bishop, now edited
in Fen

Well, a white bishop suddenly appearing on d3 changes everything. The g6 pawn is now a major problem for black. With white to move (as indicated by your fen) black is just lost. The knight on h4 is en prise. White can just take it. Here's what happens if black tries to recapture.
[fen "2rq2kr/p1ppbp2/1pn1p1pP/4P3/3P2Qn/2PB4/PP3P2/RNB1K2R w - - 0 1"]

1. Rxh4 Bxh4 2. Bxg6 fxg6 (2...Kf8 3. Bxf7 Kxf7 4. Qg7+ Ke8 5. Qxh8+ Ke7 6. Qg7+ Ke8 7. h7) 3. Qxg6+ Kf8 4. Qg7+ Ke8 5. Qxh8+ Ke7 6. Qg7+ Ke8 7. h7


How to deal with the pinned knight on f3 in the Ruy Lopez (as white)?

Black cannot exploit the pin with ...Nd4: not at once because the Nc6 itself is pinned, not later because c2-c3 is on your plan anyway. This means that you should not panic and can concentrate on developing before taking measures about the Bg4.

You should not be afraid of a ...Qf6 either. After the later sequence ...Bxf3, Qxf3, Qxf3, gxf3, your king is secure thanks to the queen exchange, and the bishop pair is much more important than the temporary doubled pawn that you would get rid of by pushing f3-f4, gaining influence in the center in the process.

If you follow a Ruy Lopez plan anyway: c3, d3, Nbd2, Re1, Nf1 you have various ways of breaking the pin.

First, you can move your queen when the second knight is on d2. Plus: it is faster. Minus: your queen don't have so many great square to go to, since on c2 it is a bit passive and that square is better left for a possible retreat of the Bb5.
Second, you continue, after Nf1, with h3 (check whether the opponent can reply ...h5 when his rook is still on h8) and after ...Bh5, Ng3. It is part of your plan anyway (reinforce e4 so you can push d3-d4, possible knight-hops to f5 or h5) and it embarass Black's light-squared bishop. After an eventual ...Bxf3 Qxf3, you gain the bishop pair with excellent chances to build an initiative on the light squares.


Does a KQQ vs KQ endgame position with perpetual check exist?

The position given by Akavall is indeed a draw by perpetual, but it's a bit difficult to see because White has many different options at some moves. They can even choose to sacrifice the h2 queen, which effectively ends the perpetual (but it's still a draw).
A position where this is much easier to see is the following one:
[FEN "5k2/8/8/8/8/5q2/7Q/6QK w - - 0 1"]

1. Qgg2 Qd1+ 2. Qhg1 Qh5+ 3. Q2h2 Qf3+

White has two options each move, and the black queen simply moves to the opened line/diagonal. As mentioned in the comments, White could sacrifice a queen on f1 or h3, but even then Black can force a perpetual on f1 and h3 (though the easiest way to draw is then trading the last pair of queens).


This line is not very popular because black can challenge the bishop with 7…h6.
Now white is forced to exchange his bishop against the knight, either by taking right away 8.Bxf6 or after 8.Be3 Ng4. This is something you'd rather avoid, though its not immediately problematic for white.

If you try to avoid this with 8.Bh4 you run into 8…Nxe4. I actually lost a game like this, if I remember correctly, some 10 years ago.

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6
7. Qd2 h6 8. Bh4 Nxe4


What is the draw frequency for 3 consecutive games (same players; amateur level)?

Definitely not impossible! It is true that draws are less frequent in amateur chess, and it is also true that draws are less frequent for faster games (how fast was the game in the show?), but even so, let's say that for a blitz game between evenly matched amateurs the draw frequency were 5%, or 1/20. If you played three games, the odds of playing three draws would be 1/8000, which while unlikely, is hardly "impossible". This is assuming that the probabilities are independent, which may not be entirely true but I think is close enough for a rough estimate.

I don't have an academic citation, but if you want some stats for online games you can look at the Lichess opening book: https://lichess.org/analysis . Normally it shows master-level games, but if you click on the settings you can chose to look at Lichess games instead, and filter by rating and time control. For blitz games at rating 1600, the draw frequency is 4-5%, depending on the opening move (the draw is the small gray stripe without a percentage, so you have to compute it by difference):

For the highest ratings, it's closer to 10% for blitz. And for classical chess, as you know, it's about 50% for top-level chess. For amateur chess I'd say maybe 10-20% but it depends on which level of amateur we are talking about. I won't cite the Lichess stats here because even though they have a "classical" category, it's really what would called rapid in over-the-board tournaments (30 min games in Lichess; OTB classical is usually 2 hours or more).


In Sicilian Defense with pawn structure as in Scheveningen, what should black do when playing d5 does not look so good?

It is generally true that, especially in the Najdorf variation, Black does not get to play ...d5 at any point early in the opening: if they do they have basically solved all the opening problems and acquired an equal if not superior position. Conversely, White's plan is to get a grip on d5 and make it the whole point of the opening, very often playing a set-up with "good Knight versus bad Bishop" (there is a good lecture with examples of the Saint Louis Chess Club here).

However, in the standard set-ups of the Najdorf variation (especially against the English attach 6.Be3 or the classical line with 6.Be2) Black plays 6...e5 themselves to avoid White from doing so (unless White plays f4 and then e5, but they have to spend two more tempi to do so) and to get their fair share of the centre. Black's bishop if often deployed in e6 and not in b7 to avoid Bc4.

A good example of this approach is the game Carlsen vs So (Sinquefield Cup (2015)).

  Secondly, sometimes white pushes their pawn to c4 to block my ...d5. What could be a good strategy for black after c4?

If White plays the standard open Sicilian set-up with 5. Nc3 then they cannot play c4 easily; Black will play ...b5 in most of the Najdorf set-ups (also allocating a Knight in c4 if allowed). Therefore the general rule is to avoid White to play c4 rather than worrying after c4 was played. If otherwise White plays an early c4 (Maróczy variation) then this is a completely different line to be analysed and does not fall in the scope of the Najdord (or Scheveningen) variation.

As a general rule, by playing the Najdorf variation, Black allows d5 to be weak, gaining back their fair share of the centre with ...e5 and counterplay on the Queen's side with ...b5 sooner or later. Moreover Black will always try to preserve their Knight on f6 and if possible play Nbd7-Nb6 and Be6 to have three pieces looking at d5. If White really wants to use that square they must do so at the cost of many tempi and converging all of their pieces there, which leaves room for counterplay meanwhile.


What are the main differences between 2...d5 and 2...e5 in the anti-Caro-Kann?

I don't play this from either side, but apparently 2... d5 leads to positions known as isolated queen pawn (isolani) which can also result from many other openings. Look it up, there is lots of information out there about this. There is a fairly standard plan in these positions. White wants to avoid getting into an endgame where the pawn would be a weakness. Typically black would try to control the square in front of the isolani (i.e. d5 in this case) preventing white from exchanging the pawn playing d5 himself. White usually has a bit more active play in the middle-game.

I don't like 2...e5. If white attacks the e5 pawn, e.g. with 3. Nf3, black is almost forced to play 3...d6 and the set-up with pawns on e5,d6 and c6 is gernerally not good. White can later play d4 and open the d-file after which the pawn on d6 might get weak.


Is the Four Pawns Attack against the Alekhine opening promising for White?

There's a concept in chess called the equilibrium. Basically, things start off more or less equal, and both sides try to upset the equilibrium in their favour (i.e., gain an advantage). If one side makes a mistake and upsets the equilibrium in their opponent's favour, then their opponent is "justified" in playing in some way to capitalize on this mistake. This often involves being aggressive and attacking. If it weren't for the mistake, the equilibrium would be maintained, causing such an attack to not work and be rebuked (assuming optimal play).
I don't know whether the Four Pawns Attack is the best line against the Alekhine, but at the very least it's one of the best. The reason it works is that White is justified in playing this way. Black has spent multiple tempi moving his knight around the board, mainly for the sake of provoking White's pawns forward. This upsets the equilibrium a bit in White's favour, giving him a free hand to be aggressive without getting punished.
Meanwhile for the KID, the opening is generally quite well regarded. Black develops quickly and is basically being no-nonsense in his approach; this ensures the equilibrium more or less gets maintained. Therefore, White isn't as justified in attacking so early on. He can certainly try with the Four Pawns, and while he's still equal Black has the resources to defend effectively.
Also, while it's true that the KID doesn't control the centre much on the first few moves, it is of those openings where Black can get away with this. So this doesn't drastically upset the equilibrium in White's favour.


Based off your position; I let the engine play it out and the below was the "best" output I received. This is just an old fashioned slog for the centre. A lot of trading going on.
[Event "Analysis Request"]
[Site "?"]
[Date "2020.09.09"]
[Round "?"]
[White "Unknown"]
[Black "Unknown"]
[Result "*"]
[SetUp "1"]
[FEN "rnbqkb1r/ppp2ppp/8/4N3/4n3/8/PPP2PPP/RNBQKB1R w KQkq - 0 1"]
[PlyCount "10"]

1. Qe2 Qd5 2. Nd3 Be7 3. f3 Nd6 4. Nf4 Qc6 5. Nd3 O-O *

1. Qe2 Ngf6 2. Nd2 Qd5 3. Nxe4 Nxe4 4. Qb5+ c6 5. Qxd5 cxd5

Based of the board;
Blacks castled to safety, the white Queen is in danger of (Re8 ... Bh4+). White feels "under developed" and has less control of the board.


First you need to install this library:

pip install python-chess

And make sure you're using the right pip, because still in some Linus distros pip and python are python 2.x and for python 3.x you should use pip3 and python3. If you want to check try this:

pip --version

You will see an output like this that will tell you what python you're using, in my case it's 3.8:

  pip 19.2.3 from /usr/lib/python3.8/site-packages/pip (python 3.8)


It seems to me that draw is all Black can get, but maybe I am wrong?

I didn't see a thing, and nether did Stockfish.

[Title "Black to move"]
[StartFlipped "0"]
[fen "3r4/p3Q1pk/1pp3p1/8/3qP3/P7/1P3RPP/6K1 b - - 0 1"]

1... Rd6 2.Qh4+ (2.Qxa7?? Rf6 ) Kg8 3.Qh3 Qe5 4.Qc8+ Kh7 5.Qh3+ Qh5 6.Qxh5+ gxh5 7.b4 Kg6 8.Rf8 Rd4 9.Rc8 Rc4 10.Ra8 Rxe4 11.Rxa7 Rc4 12.Kf2 Rc2+ 13.Kf3 b5 14.a4 bxa4 15.Rxa4 h4 16.Ra6 Kf5 17.Ra5+ Kf6=

Just because there's no forced win doesn't mean the game is without tension and opportunity. I have lost games similar to this game after move 12.


The analysis of this position seems quite reasonable based off an immediate glance of the board. Grachev has the advantageous position as he is first to move in this position which is essential for this end game play out. The c5 pawn is key to Grachevs success and without playing out the whole game immediately moving to defend it with the King is the most route to success. Dubov is incapable of promoting on the King side of the board and the double pawns do provide somewhat of a hinderance to Dubovs position.
This is effectively how the game rolled out to my understanding of it, Grachevs king charged at the c5 pawn, Dubovs and Grachevs Bishops began gobbling up pawns and White ultimately used the king to progress the queen side pawns on the A and C file to the point Dubov resigned.
In regards to the definitively analysing with modern engines. Using Komodo Dragon against itself for 10 games, in all 10 games White won. In this position, white is better in all key lines ranking from +3.53 (in the best line for White) to +1.4 in the worst line.


Why 5...h6 in the Tartakower Queen's Gambit Declined and not in the Orthodox Variation?

2 main reasons:

The orthodox defense typically goes for a ...c6 structure and avoids ...b6 + ...c5. This makes Bxf6 a more viable option for White due to the more closed nature of the game. So, ...h6 could just end up wasting a tempo by nudging White to make a somewhat favourable exchange. Note that it's fine for you to play Bxf6 against the Tartakower too, it just works better against the orthodox.
The orthodox could see Black doing the maneuver Nbd7-Nf8-Ng6 (especially if White goes for a Carlsbad by exchanging on d5). This requires control over the g6 square if White has a Qc2+Bd3 battery set up. If Black has already played ...h6 and then plays ...Ng6, White wins a pawn with Bxg6 fxg6 Qxg6.


Difference between 7. Qc2 vs 7. Qa4 in the Catalan

As you mentioned, 7.Qc2 a6 8.Qxc4 and 7.Qa4 a6 8.Qxc4 lead to the same position.

However, after 7.Qc2 a6, white has the option to play 8.a4, which is recommended by GM Avrukh in Grandmaster Repertoire 1A: The Catalan. According to the Game Database of ChessTempo, 8.a4 is a bit more popular than 8.Qxc4.
Having the choice of 8.a4 and 8.Qxc4 is probably the main reason why 7.Qc2 is played so much more often than 7.Qa4.

On the other hand, 7.Qc2 allows 7....b5, a move that became popular on the highest level only recently. For example, see Ding Liren-Carlsen.
So, if white prefers to play 8.Qxc4 after 7....a6, it makes sense to choose 7.Qa4, which occurred in Caruana-Duda.

After 7.Qa4, there are some sidelines you might consider as black: 7....Qd5 (played in Adly-Aronian (blitz)) and 7....b6.

      [StartPly "12"]

      [FEN ""]
      1.d4 Nf6 2.c4 e6 3.g3 d5 4.Nf3 Be7 5.Bg2 O-O 6.O-O dxc4 7.Qc2 (7.Qa4 a6 (7...b6)(7...Qd5) 8.Qxc4) a6 (7...b5) 8.a4 (8.Qxc4)


Your acquaintance is right, and wrong to some degree, since before chess went to Persia, its precursor is considered to have been invented in India. It was based on troop movements there, so they had already been established by then, even if they were later modified.

This is taken from Wikipedia here:

  Precursors to chess originated in India during the Gupta Empire.
  There, its early form in the 6th century was known as chaturaṅga,
  which translates as "four divisions (of the military)": infantry,
  cavalry, elephantry, and chariotry. These forms are represented by the
  pieces that would evolve into the modern pawn, knight, bishop, and
  rook, respectively."


Does anyone have a version of the 50x50 article by Nikita Plaksin?

Hi Arnaud thanks for your question.

The problems themselves can all be found in pdb.dieschwalbe.de. Type K='50' AND A='Plaksin' AND S='Problem' AND YEAR='1979'. All 50 are there numbered, with solutions. If you are typing from a phone make sure that you select the correct single-quote character: the vertical one.

The query reveals that they were published in the now-defunct magazine Problem, but it does not give the article text. I suggest Arnaud that you send your request to the Retro Mailing List retros@janko.at. This will put you in touch with all the current retro greats who would probably love to hear from you.

If that doesn’t work then let me know and I will approach someone individually.

EDIT: the 50x50 article is now available at https://www.janko.at/Retros/Articles/index.htm in Russian but I guess that google translate will work - and the diagrams are the not important part.


Chess Hustlers in the Park/Street: Where do they place in terms of skill?

Movies like to present "chess hustlers" as playing chess for a living.

In reality, most of these people are playing chess for fun.  The "hustlers" are often just down on their luck financially and like to make some money while still having fun.

There's certainly no J.J. Peachum-type figure who trains chess players to go into parks and make money from innocent passersby.

As for their strength, it's entirely dependent on the city or area you're looking.  They're just a collection of chess players, there's no strength range you have to be in.  In New York, master-strength players have been known to hang out on the street playing chess.  In New Orleans you could catch a world-class player like Jude Acers sitting around in his red beret taking all comers.  Where I am, in Cleveland, it seems like the strength level is in the 1000-1800 range, but hey I'm 2050 and I play around there fairly often, and I've known masters and even an IM to join in at various times.  The guys who are into gambling are usually among the stronger players in their setting, which is again entirely dependent on where you look.  At any rate, gambling isn't as common as the movies like to make it out to be.  Having played all over I've only encountered it a few times and usually not from secret masters but rather guys who had learned enough tricks over the years to be able to beat most clueless people and were pretty confident.

It's not a business operation, it's an informal chess club where gambling is a part of the culture.


Is it sportsmanlike to waste opponents' time by giving check at the end of the game?

That only works in blitz time controls with no increment. If you accept games with no increment you are basically agreeing that flagging is part of the game and sportsmanlike. If you personally find it unsporting then always play with an increment and decline challenges with no increment.


6x6 chess exist. See this page from Wikipedia:
http://en.wikipedia.org/wiki/Minichess#6.C3.976_chess.


Is the Sveshnikov Variation a subvariation of the Lasker-Pelikan Variation?

There is no central authority for opening names, and the ones used shift over time. So a definite answer to this question isn't possible.

Bad_Bishop quotes Silman's review of "Sicilian Sveshnikov: Move by Move", which is a bit odd as the book itself treats all variations after 5...e5 (see the PDF preview of the book, chapter "Sixth Move Alternatives".

The same is true of "The Sicilian Sveshnikov" by Kotronias (PDF preview).

But these are repertoire books for black; if you play 5...e5 and white wants to, he can basically force 6.Ndb5 d6 7.Bg5 a6 8.Na3 b5 as there are few serious alternatives for black. So if you play the Lasker/Pelikan, you play the Sveshnikov too, and vice versa. It's logical that they want to treat white's alternatives at move 6 too, so that the book is more widely useful. But then, why not call it "The Lasker/Pelikan: Move by Move"?

I think the name "Lasker/Pelikan" is obsolete, at least in English language chess publications. I've never seen it used in any book or periodical or website in at least twenty years, it's always Sveshnikov. You can easily find many books on the Sveshnikov, and I don't know any on the Lasker/Pelikan. Apart from that Silman review, but he has played chess for a long time.

ECO (and thus the Informant) calls it the Lasker/Pelikan, but its codes and their names are set in stone since the 1960s. Those codes and their names have also ended up in many computer files of opening names, but as far as I can see it's not actually used by anybody anymore.

It's just the Sveshnikov.


AlphaZero trained itself by self-playing. It used the gradient descent algorithm for convergence (equation 1 in the paper). Please note the training phase had nothing to do with Stockfish.

Later, Google matched the "fully trained" AlphaZero against Stockfish. It's like you practice chess with yourself for four months, participated in a tournament then won all your games!

Hardwares were different in training and playing:

  Training proceeded for 700,000 steps (mini-batches of size 4,096) starting from randomly initialised parameters, using 5,000 first-generation TPUs (15) to generate self-play games and 64 second-generation
  TPUs to train the neural networks.

and

  ... in chess, shogi and Go respectively, playing
  100 game matches at tournament time controls of one minute per move. AlphaZero and the previous AlphaGo Zero used a single machine with 4 TPUs...


Tablebases are databases of endgame positions, with few pieces left on the board (say a 5-man tablebase, which consists of all legal positions with 5 pieces on the board in total, including kings, say K+Q vs. K+R+B). These databases have the positions 'connected', i.e. they also contain the moves to get from one legal position to another (in particular, moves that eventually lead to mate). This allows a chess program, in such positions, to look straight into the tablebase, rather than to calculate via the engine.

Tablebases are perfect, in the sense that it can tell you number of moves to mate, and playing a position against a program using tablebases (in positions with very few pieces left) is akin to "playing with god". So as an advantage, they save computational time and allow your machine to play certain endgame positions perfectly. The disadvantage is that they take up a large amount of memory space.

Owing to the memory issue, compression techniques help to reduce the space taken up by the tablebases. Syzygy tablebases are relatively new (introduced about 2 years ago), compared to the Nalimov tablebases which have been around for quite a while (itself being a compression improvement over previous tablebases). The Nalimov 6-man tablebases take up over 1TB of memory space, whereas the Syzygy bases use less than 200GB.

The different names in front of 'tablebases', e.g. Syzygy and Nalimov, refer to nothing more than compression methods. For all practical purposes, there is absolutely no difference between the content of Syzygy and Nalimov tablebases; a computer that uses either one will play at the same strength (perfect!). Their only difference is the memory space they occupy.

(The possible difference in content, if any, is subtle: first off, every legal position in the tablebase has an evaluation attached to it (draw/win/loss in X moves). However, some positions may contain a sequence of moves to mate that require breaking the 50-move rule; the evaluations of these positions in the tablebases may be changed to accommodate for this, e.g. W/L/D/"win but break 50-move rule", but in any practical game, you are pretty much guaranteed that you will never see this difference.)


Chess Tempo #97369 - Is the problem's solution wrong?

I believe black can do no better than a draw from the starting position. First I'll give my own reasoning for it (and everything I'll say I've checked with Houdini, to rule out silly oversights on my part). Further below, I will suggest what I think is a very plausible explanation for why Chess Tempo's engine might have gotten it wrong.

The first move

1... Rb4

is forced, as it is the only way to keep white's b-pawn from queening without losing the rook. In turn, white's reply

2. Rb1

is forced, because without the b-pawn white will certainly be losing. Now white is threatening 3. b8=Q, which would force black to give up the rook. Since 2... Rxb1+ 3. Qxb1 doesn't help, black is thus forced to play

2... Qb6

Again white cannot let the b-pawn fall for nothing, and so has no choice but to play the sequence

3. Rxb4 Qxb4 4. Qa6

to stop black's threat of ...Qxb7. Now it is black to move from the following position:

[FEN "6k1/5p2/1Pp3pb/2q4p/1rNpPP2/3Q2PP/8/5RK1 b - - 0 1"]
[StartPly "9"]

1... Rxc4 2. b7 {Last given ply, white threatens b8=Q+} 2... Rb4 {First original move, prevent pawn promotion without loosing rook} 3. Rb1 {preserve pawn to avoid loosing}
3... Qb6 (3... Rxb1+?? 4. Qxb1 {pawn is just about promoted}) 4. Rxb4 Qxb4 5. Qa6 {black must now give perpetual check to avoid loosing}

Black would love to consolidate the position by getting the bishop to a spot where it eyes the b8 square along with black's queen (say by ...Bf8 followed by ...Bd6); doing so would eliminate any danger of white's pawn promoting, and allow black to regroup and win easily with the extra bishop. Unfortunately, if black tries 4... Bf8, then 5. Qa8 threatens to promote and simultaneously pins the bishop, preventing 5... Bd6. In that case, black has no better option than to play 5... Qe1+ and put white into perpetual check, draw. So 4... Bf8 doesn't work, but any other direct try by black to impede the advance of the b-pawn will just be slower. The problem is that, from the diagram position (meaning my diagram), black's forces are just uncoordinated enough that he doesn't have enough time to prevent Qa8 and promotion of the b-pawn directly, and must instead go in for perpetual check.

From a broad conceptual point of view, black has only one other idea to try and play for a win if he can't stop the b-pawn: to run his own d-pawn to promotion. But it's easy to see that that plan is also too slow. If black tries 4... d3, then after the white response 5. Qa8+ Kh7(g7) 6. b8=Q, black's queen is en prise and white is now threatening to mate. So black would again be forced to bail out and go for a perpetual check with 6... Qe1+.

What I think went wrong here

From your initial diagram position, an engine could search to a pretty healthy depth and keep seeing positions in which black retains a sizable material advantage (a full extra bishop). The reason for this is that though black cannot "really" stop the b-pawn from queening, he can give checks to push that event into the future, further down the engine's search. Now, of course, once an engine sees repetitions of the position in its search, it will recognize the draw and no longer see any advantage from the extra material. But ... (and this next part is indeed speculation, but it is not without sense)

A potentially problematic feature of this particular position, though, is that black doesn't just have, say, two checking squares from which the queen can carry out the perpetual. Checks can happen on e1, d2, d1, c2, c1, b2, b1 and in the meantime the white king could have at least 10 squares it could travel on; not to mention, a checking sequence could also get interrupted by, say, the white queen blocking a check, followed by the black queen getting back behind the b-pawn, and then the white queen returning to a6.

The point being, there are very many possible paths here; it's all still just a perpetual check, but the great variety of options here could make it so that, at whatever search depth it's working at in the Chess Tempo evaluation process, the engine couldn't quite see a repetition yet, because it keeps seeing things like, e.g. "Oh, I don't have to repeat with ...Qe1+, I'll check from d1 this time instead," pushing the recognition of a perpetual check beyond its horizon.

Again, I'm speculating, but it's at least not a nonsensical possibility.


Moving the king is the only way to escape a double check.  There is no possible other move that will block both checks.


Let's check forcing moves first.

1... Qxf2 is definitely draw.

[FEN "8/8/8/2p1p3/2Pp2P1/1knP4/3q1QK2/5B2 b - - 0 1"]

1... Qxf2 2. Kxf2 e4 (2...Kc2 { transposes to main line}) {Nd1, or Na4 too slow, so e4 is the only option. Kc2 transposes to this line.} 3. Kg3! (3. g5? Kc2 {Both sides queen, but black remains with extra pawns, winning for black}) (3. dxe4? Nxe4+ {Threatening with fork, if Black exchanges minor pieces, it's a winning pawn endgame for Black} 4. Ke1 Kc3-+ {White has to give up bishop for d pawn, and White's pawn is going nowhere} (4. Kg1 Kc3-+ {White has to give up bishop for d pawn, and White's pawn is going nowhere}) (4.Kg2 Kc3-+ {White has to give up bishop for d pawn, and White's pawn is going nowhere}) {White has to give up bishop for d pawn, and White's pawn is going nowhere}){Not letting Black to get tempo while marching to queen} Kc2 4. dxe4 d3 5. Bxd3+ Kxd3 6. Kf4 Nxe4 7. Ke5=/= {Lomonosov}

So we know that Black at least has draw. But I feel Black should win in this position. Bishop is not active, but knight is doing very good, especially when it lands to e3. Also Black's king is very active, can easily eliminate White's remaining pawns if both sides queen. So, Black probably has a winning continuation.

Some ideas:

[FEN "8/8/8/2p1p3/2Pp2P1/1knP4/3q1QK2/5B2 b - - 0 1"]

1... Qc1 {This move feels best for me. It puts the queen to h6-c1 diagonal to block white pawn which I think important. Qg5 is an alternative} (1...Qg5) 2. Qg3 {Attacking e-pawn, supporting b-pawn} Nd1 {Knight is heading to e3} 3.Be2 {Activating bishop, not much alternative though} Ne3+ 4. Kf2 Kc3 { Attacking d3} 5. Qxe5 Kd2 { Threatening Qe1, taking bishop} 6. Qh2 { Defends bishop } Qe1 7. Kf3 Nxg4 {Wins a pawn} 8.Qf4 Ne3 {Bishop is hanging again} 9. Qh2 Qb1

Resulting position looks very promising for Black. But of course, the line is not forced, so, this continuation may not be the best. Anyway, it should give an idea to decide how to proceed in starting position.

Conclusion

I believe, Black should not play 1...Qxf2, instead should look for a win. Black should centralize the knight to e3 square, put the king into c3, where it attacks d3, should try to force White to give up g-pawn by pressing on g-pawn and bishop same time, knowing that bishop is blocked by allied pawns, and pretty much stands as a target to attack in White's crampy king-side.

Testing my Findings with Monte Carlo Simulation

I run a 10 game Manto Carlo simulation where each side has 10 minutes to finish the game. In all games, black went for the line above, starting with ...Qc1, and won all games.

[Event "?"]
[Site "?"]
[Date "2015.12.28"]
[Round "1"]
[White "Stockfish 261014 64"]
[Black "Stockfish 261014 64"]
[Result "0-1"]
[FEN "8/8/8/2p1p3/2Pp2P1/1knP4/3q1QK1/5B2 b - - 0 1"]
[PlyCount "67"]
[SetUp "1"]
[TimeControl "100/600"]

1... Qc1 { +1.68/24 11s}  2. Qg3 { -1.63/25 12s}  2... Nd1 { +2.40/25 7.4s}  3.
Be2 { -2.36/25 15s}  3... Ne3+ { +2.57/24 7.4s}  4. Kf2 { -2.68/25 12s}  4...
Kc3 { +2.71/25 11s}  5. Qxe5 { -2.85/26 14s}  5... Kd2 { +3.28/27 11s}  6. Qh2
{ -3.47/27 17s}  6... Qe1+ { +3.34/26 7.4s}  7. Kf3 { -3.47/1 0.001s}  7...
Nxg4 { +3.58/27 15s}  8. Qf4+ { -3.47/25 7.2s}  8... Ne3 { +3.58/28 7.3s}  9.
Qh2 { -3.75/25 17s}  9... Qb1 { +3.87/26 40s}  10. Kf2 { -3.05/25 7.1s}  ( 10.
Bf1+ { -3.72/27 30s}  10... Kc3 { +3.72/26 5.7s}  11. Be2 { -3.40/27 6.9s}
11... Qb6 { +3.96/26 17s}  12. Kf2 { -3.80/22 23s}  12... Qf6+ { +5.22/27 17s}
13. Kg1 { -4.60/25 14s}  13... Qg5+ { +5.67/28 12s}  14. Kf2 { -4.97/25 33s}
14... Nf5 { +5.88/29 5.3s}  15. Qh3 { -4.93/23 8.4s}  15... Qf4+ { +6.20/25
7.2s}  16. Qf3 { -4.55/26 9.6s}  16... Qh4+ { +10.93/36 49s}  17. Kg1 {
-4.42/26 6.2s}  17... Ne3 { +28.79/28 7.8s}  18. Qf2 { -52.13/37 17s}  18...
Qxf2+ { +52.11/36 7.1s}  19. Kxf2 { -62.24/39 13s}  19... Kd2 { +54.84/37 4.6s}
 20. Bf3 { -89.07/39 19s}  20... Kxd3 { +58.23/38 32s}  21. Bh5 { -123.53/38
9.0s}  21... Nxc4 { +62.79/41 5.9s}  22. Bd1 { -123.53/37 5.7s}  22... Kc3 {
+M73/35 8.8s}  23. Bg4 { -298.86/37 19s}  23... d3 { +M69/35 8.1s}  24. Ke1 {
-M42/36 44s}  24... d2+ { +M47/35 8.8s}  25. Kf2 { -M36/37 17s}  25... Nb2 {
+M35/36 3.9s}  26. Ke3 { -M34/37 14s}  26... d1=Q { +M31/36 7.0s}  27. Bxd1 {
-M32/36 4.4s}  27... Nxd1+ { +M29/36 3.9s}  28. Ke2 { -M26/36 9.0s}  28... Kc2
{ +M27/35 3.8s}  29. Ke1 { -M24/35 9.8s}  29... c4 { +M25/34 3.8s}  30. Ke2 {
-M22/35 4.1s}  30... c3 { +M21/34 3.8s}  31. Ke1 { -M20/33 7.8s}  31... Kb2 {
+M19/33 3.8s}  32. Kxd1 { -M18/42 5.4s}  32... c2+ { +M17/40 3.7s}  33. Ke2 {
-M16/51 3.9s}  33... c1=Q { +M15/48 3.7s}  34. Kf2 { -M14/66 5.4s}  34... Qf4+
{ +M13/71 3.7s}  35. Kg2 { -M12/120 4.0s}  35... Kc3 { +M11/120 3.0s}  36. Kh3
{ -M10/120 0.31s}  36... Kd2 { +M9/120 0.079s}  37. Kg2 { -49.17/1 0.001s}
37... Ke2 { +M7/120 0.015s}  38. Kh3 { -M6/120 0.039s}  38... Qg5 { +M5/120
0.012s}  39. Kh2 { -M4/1 0s}  39... Kf2 { +M3/120 0.005s}  40. Kh3 { -M2/120
0.001s}  40... Qg3# { Stockfish 261014 64-Stockfish 261014 64 2015.12.28}  ) (
10. Bf1+ { -3.74/26 29s}  10... Kc3 { +3.81/25 47s}  11. Be2 { -3.25/26 6.9s}
11... Qb7+ { +3.87/26 32s}  12. Kf2 { -3.57/27 11s}  12... Qb6 { +3.93/26 40s}
13. Ke1 { -3.57/25 22s}  13... Qf6 { +8.13/28 7.3s}  14. Qf2 { -6.34/27 13s}
14... Qg6 { +13.22/29 11s}  15. Qh2 { -14.05/28 14s}  15... Qg2 { +21.86/33
7.4s}  16. Qxg2 { -39.84/32 10s}  16... Nxg2+ { +52.18/37 6.6s}  17. Kf2 {
-57.87/37 13s}  17... Nf4 { +54.92/37 4.5s}  18. Bf3 { -64.66/38 40s}  18...
Nxd3+ { +61.64/38 13s}  19. Kg3 { -73.95/38 16s}  19... Nb2 { +123.52/38 6.1s}
20. Kf4 { -123.13/37 52s}  20... d3 { +123.55/37 9.1s}  21. Bg4 { -123.19/36
13s}  21... d2 { +123.56/36 6.3s}  22. Ke3 { -74.63/34 44s}  22... d1=Q {
+298.95/34 4.3s}  23. Bxd1 { -M40/33 5.8s}  23... Nxd1+ { +M33/35 8.1s}  24.
Ke2 { -M32/36 6.5s}  24... Nb2 { +M31/35 4.2s}  25. Ke3 { -M30/35 7.3s}  25...
Kxc4 { +M27/35 4.5s}  26. Kd2 { -M26/35 8.2s}  26... Kb3 { +M25/34 4.2s}  27.
Ke2 { -M24/33 5.3s}  27... c4 { +M23/31 4.2s}  28. Ke3 { -M22/31 7.2s}  28...
c3 { +M21/32 4.2s}  29. Kf3 { -M20/30 5.2s}  29... c2 { +M17/29 4.2s}  30. Ke4
{ -M16/30 6.5s}  30... c1=Q { +M15/30 4.8s}  31. Kf5 { -M14/32 6.6s}  31... Qh6
{ +M13/33 4.7s}  32. Kg4 { -M12/42 4.8s}  32... Qg6+ { +M11/41 4.3s}  33. Kf4 {
-M10/112 4.8s}  33... Nd3+ { +M9/106 4.1s}  34. Ke3 { -M8/120 0.047s}  34...
Qf5 { +M7/120 0.10s}  35. Ke2 { -M6/120 0.013s}  35... Kc2 { +M5/120 0.014s}
36. Ke3 { -M4/1 0s}  36... Qf4+ { +M3/120 0.003s}  37. Ke2 { -M2/1 0.001s}
37... Qf2# { Stockfish 261014 64-Stockfish 261014 64 2015.12.28}  ) ( 10. Bf1+
{ -3.65/24 17s}  10... Kc3 { +3.73/26 12s}  11. Be2 { -3.80/25 11s}  11... Qb7+
{ +3.73/28 7.1s}  12. Kf2 { -4.55/26 18s}  12... Qg7 { +3.73/28 7.2s}  13. Qg3
{ -3.92/24 19s}  13... Qf6+ { +4.37/23 12s}  14. Kg1 { -4.20/26 23s}  14... Kd2
{ +5.05/25 37s}  15. Bf3 { -4.20/26 6.6s}  15... Kxd3 { +5.05/26 14s}  16. Qf2
{ -4.76/22 37s}  16... Qf5 { +5.11/26 6.6s}  17. Qe2+ { -4.76/22 6.1s}  17...
Kc3 { 0.00/1 0.001s}  18. Qe1+ { -5.27/22 17s}  18... Kxc4 { +5.82/23 15s}  19.
Kf2 { -6.03/21 13s}  19... Kb3 { +6.00/23 9.7s}  20. Qa1 { -6.72/23 22s}  20...
Qc2+ { +6.13/23 22s}  21. Kg3 { -6.40/25 51s}  21... c4 { +6.74/22 14s}  22.
Qa8 { -7.67/22 19s}  22... Qg6+ { +9.13/21 10s}  23. Kh3 { -8.36/23 7.0s}
23... Qh6+ { +12.94/23 14s}  24. Kg3 { -11.10/25 24s}  24... Qg5+ { +13.89/24
9.6s}  25. Kh3 { -7.31/25 4.2s}  25... d3 { +14.70/25 19s}  26. Qa1 { -11.77/21
17s}  26... Kc2 { +33.72/23 10s}  27. Qa2+ { -17.01/20 7.4s}  27... Kc1 {
+49.10/26 19s}  28. Qf2 { -26.58/22 11s}  28... d2 { +62.82/27 5.4s}  29. Be2 {
-M38/25 17s}  29... c3 { +M33/25 7.6s}  30. Qf8 { -49.06/24 11s}  30... d1=Q {
+M31/27 9.2s}  31. Bxd1 { -M36/25 4.6s}  31... Kxd1 { +M27/29 5.2s}  32. Qf1+ {
-M24/32 7.0s}  32... Kd2 { +M23/32 10s}  33. Qf2+ { -M22/31 7.5s}  33... Kd3 {
+M21/35 4.9s}  34. Qf1+ { -M20/28 5.3s}  34... Ke4 { +M19/36 4.9s}  35. Qh1+ {
-M18/31 2.9s}  35... Qg2+ { +M17/39 4.8s}  36. Qxg2+ { -M16/44 2.8s}  36...
Nxg2 { +M15/56 4.7s}  37. Kg4 { -M14/58 3.8s}  37... c2 { +M13/71 4.7s}  38.
Kg5 { -M12/46 3.8s}  38... c1=Q+ { +M11/92 4.6s}  39. Kf6 { -M10/80 3.6s}
39... Qc6+ { +M9/120 1.9s}  40. Kg7 { -M8/120 0.58s}  40... Kf5 { +M7/120
0.20s}  41. Kh7 { -M6/120 0.013s}  41... Qc7+ { +M5/120 0.008s}  42. Kh6 {
-M4/120 0.003s}  42... Qb7 { +M3/120 0.003s}  43. Kh5 { -M2/1 0s}  43... Qh7# {
Stockfish 261014 64-Stockfish 261014 64 2015.12.28}  ) ( 10. Bf1+ { -3.84/28
67s}  10... Kc3 { +3.69/26 18s}  11. Be2 { -3.87/24 9.6s}  11... Qb7+ {
+3.97/25 14s}  12. Kf2 { -4.03/25 9.0s}  12... Qf7+ { +4.16/27 12s}  13. Kg1 {
-4.14/25 15s}  13... Qg7+ { +4.16/27 6.4s}  14. Kh1 { -4.62/26 37s}  14... Qb7+
{ +4.16/26 18s}  15. Kg1 { -3.02/22 8.3s}  15... Qb1+ { +4.46/27 56s}  16. Kf2
{ -3.52/23 14s}  16... Kd2 { +4.46/28 5.6s}  17. Kf3 { -3.80/24 12s}  17...
Qb7+ { +5.02/27 9.0s}  18. Kf2 { -3.94/25 12s}  18... Qf7+ { +5.02/27 5.6s}
19. Kg1 { -5.23/28 7.7s}  19... Qg6+ { +5.29/26 15s}  20. Kf2 { -5.35/29 11s}
20... Qf5+ { +5.94/26 25s}  21. Kg1 { -5.35/31 5.4s}  21... Qg5+ { +5.94/26
5.1s}  22. Kf2 { -5.99/30 49s}  22... Nf5 { +6.08/27 5.1s}  23. Bf3 { -6.03/23
7.5s}  23... Kxd3 { +6.43/26 13s}  24. Qh3 { -5.35/23 11s}  24... Kc3 {
+10.82/26 23s}  25. Qg4 { -4.73/21 8.8s}  25... Qxg4 { +60.25/35 7.2s}  26.
Bxg4 { -54.79/32 6.8s}  26... Ne3 { +M57/34 4.6s}  27. Bf3 { -123.56/34 9.2s}
27... Nxc4 { +298.91/34 7.5s}  28. Kg3 { -102.45/34 4.5s}  28... d3 {
+298.93/33 4.5s}  29. Kf4 { -298.98/31 6.1s}  29... d2 { +M71/34 18s}  30. Ke4
{ -122.62/33 37s}  30... Nb2 { +M43/34 9.4s}  31. Ke3 { -M36/34 10s}  31...
d1=Q { +M37/34 4.1s}  32. Bxd1 { -M32/35 3.8s}  32... Nxd1+ { +M29/35 4.0s}
33. Ke2 { -M26/36 4.5s}  33... Kc2 { +M27/35 4.0s}  34. Ke1 { -M28/33 3.2s}
34... Nc3 { +M25/35 4.1s}  35. Kf2 { -M26/33 3.1s}  35... Kd3 { +M23/34 3.9s}
36. Kf3 { -M22/32 4.8s}  36... c4 { +M21/32 3.9s}  37. Kg4 { -M20/32 4.0s}
37... Ne4 { +M19/32 5.4s}  38. Kf4 { -M18/34 4.1s}  38... c3 { +M17/34 3.7s}
39. Kf5 { -M16/35 4.4s}  39... c2 { +M15/35 3.6s}  40. Ke6 { -M14/36 2.7s}
40... c1=Q { +M13/36 4.3s}  41. Kd7 { -M12/39 2.7s}  41... Qf4 { +M11/42 3.7s}
42. Ke7 { -M10/63 3.5s}  42... Qc7+ { +M9/74 3.4s}  43. Ke6 { -M8/120 0.37s}
43... Qh7 { +M7/120 0.31s}  44. Ke5 { -M6/120 0.049s}  44... Qg6 { +M5/120
0.032s}  45. Kf4 { -M4/120 0.005s}  45... Qg5+ { +M3/120 0.005s}  46. Kf3 {
-M2/1 0.001s}  46... Qg3# { Stockfish 261014 64-Stockfish 261014 64 2015.12.28}
 ) ( 10. Bf1+ { -3.77/25 23s}  10... Kc3 { +3.96/28 8.4s}  11. Be2 { -2.77/25
7.0s}  11... Qb7+ { +4.11/27 21s}  12. Kf2 { -3.58/25 15s}  12... Qf7+ {
+4.58/27 57s}  13. Kg1 { -3.65/28 17s}  13... Qg7+ { +4.81/25 10s}  14. Kf2 {
-4.29/28 63s}  14... Qf6+ { +4.81/26 8.1s}  15. Kg1 { -5.62/27 8.2s}  15...
Qg5+ { +4.81/26 5.3s}  16. Kf2 { -7.01/28 19s}  16... Kd2 { +4.59/25 31s}  17.
Qh1 { -4.68/22 15s}  17... Qf4+ { +4.59/25 4.9s}  18. Bf3 { -5.41/23 13s}
18... Kxd3 { +4.65/25 4.9s}  19. Qb1+ { -4.70/23 5.6s}  19... Nc2 { +5.29/23
6.8s}  20. Qb6 { -5.13/22 18s}  20... Kc3 { +10.06/23 5.0s}  21. Qa5+ {
-11.58/23 15s}  21... Kb2 { +23.63/21 9.5s}  22. Qb6+ { -16.12/25 16s}  22...
Kc1 { +49.17/29 11s}  23. Qb3 { -17.10/27 25s}  23... Qh2+ { +52.34/34 4.8s}
24. Bg2 { -52.38/34 7.3s}  24... d3 { +52.34/34 4.8s}  25. Qxd3 { -59.72/34
9.6s}  25... Qxg2+ { +M43/38 4.8s}  26. Kxg2 { -59.72/1 0.001s}  26... Ne1+ {
+M37/38 4.8s}  27. Kf2 { -M36/39 12s}  27... Nxd3+ { +M35/37 4.8s}  28. Kg3 {
-M34/37 11s}  28... Ne5 { +M33/36 8.7s}  29. Kf4 { -M32/36 9.0s}  29... Nxc4 {
+M31/35 4.7s}  30. Ke4 { -M30/35 7.2s}  30... Nb2 { +M29/34 7.0s}  31. Ke3 {
-M24/34 9.7s}  31... c4 { +M25/34 7.3s}  32. Kf4 { -M22/33 6.4s}  32... Kd2 {
+M23/32 4.5s}  33. Kg5 { -M20/33 5.6s}  33... c3 { +M19/32 8.6s}  34. Kf4 {
-M18/31 3.8s}  34... c2 { +M17/31 4.3s}  35. Ke5 { -M16/31 6.3s}  35... Nd3+ {
+M15/30 6.5s}  36. Ke6 { -M14/34 5.8s}  36... c1=Q { +M13/33 4.1s}  37. Ke7 {
-M12/39 3.6s}  37... Qc6 { +M11/39 4.6s}  38. Kf7 { -M10/72 3.5s}  38... Ne5+ {
+M9/78 4.1s}  39. Ke7 { -M8/120 0.36s}  39... Qb6 { +M7/120 0.39s}  40. Kf8 {
-M6/120 0.034s}  40... Qd6+ { +M5/120 0.018s}  41. Kg8 { -M4/120 0.007s}  41...
Qg6+ { +M3/120 0.007s}  42. Kh8 { -M2/120 0.003s}  42... Nf7# { Stockfish
261014 64-Stockfish 261014 64 2015.12.28}  ) ( 10. Bf1+ { -3.70/24 11s}  10...
Kc3 { +3.65/29 7.6s}  11. Be2 { -3.21/24 7.2s}  11... Qb7+ { +3.93/28 20s}  12.
Kf2 { -3.54/24 20s}  12... Qf7+ { +4.26/28 26s}  13. Kg1 { -3.81/26 12s}  13...
Qg7+ { +4.26/28 6.9s}  14. Kf2 { -3.68/26 7.1s}  14... Qf6+ { +4.51/24 12s}
15. Kg1 { -3.93/22 12s}  15... Qg5+ { +4.89/26 12s}  16. Kf2 { -4.41/23 20s}
16... Nf5 { +5.10/26 6.8s}  17. Qh3 { -5.61/24 15s}  17... Kd2 { +6.68/24 16s}
18. Bg4 { -6.68/25 18s}  18... Qf4+ { +6.01/23 13s}  19. Kg1 { -5.68/25 6.6s}
19... Ne3 { +5.99/24 8.9s}  20. Bf3 { -6.95/25 12s}  20... Kxd3 { +6.86/23
9.7s}  21. Bc6 { -8.54/27 43s}  21... Kxc4 { +7.84/24 9.1s}  22. Qc8 { -8.22/24
15s}  22... Kd3 { +9.20/25 10s}  23. Qb7 { -8.96/25 12s}  23... Qg3+ { +9.26/24
9.0s}  24. Kh1 { -8.54/27 5.7s}  24... Qe1+ { +9.51/24 10s}  25. Kh2 { -8.54/1
0.001s}  25... c4 { +11.72/25 30s}  26. Bf3 { -8.05/27 5.8s}  26... Qh4+ {
+13.43/24 8.1s}  27. Kg1 { -7.84/1 0.002s}  27... c3 { +17.34/25 14s}  28. Qb1+
{ -14.91/23 11s}  28... Kd2 { +32.61/27 28s}  29. Qa2+ { -20.49/25 11s}  29...
Nc2 { +22.64/27 14s}  30. Bc6 { -49.10/27 25s}  30... Qg5+ { +48.89/28 11s}
31. Kf2 { -52.38/29 31s}  31... Qf6+ { +49.06/30 4.9s}  32. Bf3 { -52.25/31
4.6s}  32... Qh4+ { +M47/29 41s}  33. Kg2 { -52.30/30 21s}  33... d3 {
+29.63/29 35s}  34. Bd5 { -39.71/21 6.0s}  34... Kc1 { +M57/28 3.3s}  35. Bb3 {
-52.34/27 8.8s}  35... Ne1+ { +M59/27 11s}  36. Kf1 { -M58/27 8.3s}  36... Qh1+
{ +M61/29 3.3s}  37. Kf2 { -M56/1 0.002s}  37... Qg2+ { +M27/28 18s}  38. Ke3 {
-M48/31 3.8s}  38... Qxa2 { +M25/28 2.6s}  39. Bxa2 { -M26/29 6.5s}  39... d2 {
+M25/27 2.6s}  40. Bb3 { -M24/29 5.5s}  40... c2 { +M21/27 2.5s}  41. Bxc2 {
-M20/27 6.8s}  41... Kxc2 { +M19/28 2.7s}  42. Kd4 { -M16/28 6.7s}  42... d1=Q+
{ +M17/25 2.4s}  43. Ke5 { -M14/33 7.2s}  43... Qd7 { +M13/30 2.7s}  44. Kf6 {
-M12/41 4.2s}  44... Nf3 { +M11/36 2.3s}  45. Kg6 { -M10/1 0.001s}  45... Qe6+
{ +M9/61 2.3s}  46. Kh7 { -M8/120 0.57s}  46... Ne5 { +M7/120 0.36s}  47. Kh8 {
-M6/120 0.012s}  47... Qf6+ { +M5/120 0.008s}  48. Kh7 { -M4/120 0.002s}  48...
Qg6+ { +M3/120 0.003s}  49. Kh8 { -M2/1 0s}  49... Nf7# { Stockfish 261014
64-Stockfish 261014 64 2015.12.28}  ) ( 10. Qf2 { -3.63/25 22s}  10... Qb7+ {
+13.97/28 11s}  11. Kg3 { -8.02/29 18s}  11... Qg7+ { +10.42/31 63s}  12. Kh3 {
-39.78/35 27s}  12... Qg2+ { +44.66/33 8.2s}  13. Qxg2 { -48.94/38 9.3s}  13...
Nxg2 { +52.34/37 8.5s}  14. Bf3 { -57.12/38 14s}  14... Ne1 { +58.68/40 17s}
15. Be4 { -58.81/39 34s}  15... Nxd3 { +63.24/39 17s}  16. Kg3 { -33.37/38 57s}
 16... Ke3 { +73.47/39 19s}  17. Bf5 { -59.58/32 7.7s}  17... Ne5 { +73.33/38
50s}  18. Kh4 { -M44/36 19s}  18... d3 { +M45/33 7.7s}  19. Kg5 { -M38/36 8.9s}
 19... d2 { +M43/35 4.7s}  20. Bc2 { -M36/35 6.9s}  20... Nxc4 { +M35/36 4.7s}
21. Kf5 { -M34/35 7.2s}  21... Kd4 { +M31/36 5.0s}  22. Kf4 { -M30/36 8.8s}
22... Ne3 { +M29/37 7.2s}  23. Ba4 { -M28/36 5.1s}  23... d1=Q { +M27/37 4.7s}
24. Bxd1 { -M26/36 5.0s}  24... Nxd1 { +M25/35 4.7s}  25. Kf3 { -M22/37 8.0s}
25... Kd3 { +M23/35 5.4s}  26. Kg2 { -M20/38 7.6s}  26... c4 { +M19/36 4.7s}
27. Kh2 { -M18/40 6.6s}  27... c3 { +M17/39 4.7s}  28. Kg3 { -M16/42 4.9s}
28... c2 { +M15/39 4.7s}  29. Kg4 { -M14/42 7.1s}  29... Ne3+ { +M13/43 4.9s}
30. Kg5 { -M12/55 6.6s}  30... c1=Q { +M11/55 4.8s}  31. Kg6 { -M10/84 4.7s}
31... Qc6+ { +M9/111 4.7s}  32. Kg7 { -M8/120 0.87s}  32... Nf5+ { +M7/120
0.070s}  33. Kf7 { -M6/120 0.004s}  33... Kd4 { +M5/120 0.009s}  34. Kg8 {
-M4/120 0.005s}  34... Qf6 { +M3/120 0.004s}  35. Kh7 { -M2/1 0.001s}  35...
Qg7# { Stockfish 261014 64-Stockfish 261014 64 2015.12.28}  ) 10... Qb6 {
+3.62/23 11s}  11. Qh8 { -3.81/24 39s}  ( 11. Bf3 { -4.08/25 59s}  11... Kxd3 {
+3.94/21 8.7s}  12. Qg1 { -4.12/21 23s}  12... Qb2+ { +4.08/20 11s}  13. Kg3 {
-4.43/21 14s}  13... Nxc4 { +4.41/21 26s}  14. Bh5 { -4.24/21 29s}  14... Ne3 {
+4.63/21 12s}  15. Bg6+ { -4.65/20 14s}  15... Kc3 { +4.75/22 30s}  16. Kf3 {
-4.94/23 44s}  16... c4 { +5.45/22 7.8s}  17. Qe1+ { -4.99/21 13s}  17... Kb3 {
+6.49/23 5.6s}  18. Ke4 { -5.93/23 16s}  18... c3 { +6.97/23 5.6s}  19. Kd3 {
-7.31/22 12s}  19... Ka3 { +7.49/24 9.0s}  20. Qh1 { -8.99/22 20s}  20... Qd2+
{ +11.19/20 7.8s}  21. Ke4 { -8.99/1 0s}  21... c2 { +11.39/22 13s}  22. Qa1+ {
-13.00/18 5.3s}  22... Kb4 { +12.91/23 23s}  23. Qb2+ { -8.88/18 6.0s}  23...
Kc5 { +13.14/24 30s}  24. Qa3+ { -10.71/20 9.4s}  24... Qb4 { +14.12/25 40s}
25. Qc1 { -11.76/22 13s}  25... Qc3 { +14.09/25 6.1s}  26. Kf3 { -17.11/23 19s}
 26... Nf5+ { +14.15/25 35s}  27. Kg4 { -19.91/23 26s}  27... Qd3 { +18.03/21
7.0s}  28. Qf4 { -19.98/19 5.5s}  28... Qd1+ { +10.94/20 5.0s}  29. Kxf5 {
-20.46/19 8.4s}  29... c1=Q { +11.15/21 3.2s}  30. Qc7+ { -16.23/20 13s}  30...
Kb4 { +18.18/18 4.9s}  31. Qb7+ { -16.35/21 18s}  31... Kc3 { +23.17/20 10s}
32. Qc7+ { -13.56/15 2.3s}  32... Kb2 { +39.71/21 4.3s}  33. Qb6+ { -11.17/15
4.9s}  33... Ka3 { +28.70/22 9.8s}  34. Qd6+ { -21.64/18 9.3s}  34... Ka2 {
+18.53/22 8.0s}  35. Bf7+ { -20.06/20 1.4s}  35... Kb1 { +49.10/25 2.5s}  36.
Qb8+ { -49.02/21 3.4s}  36... Qb2 { +M67/25 8.9s}  37. Qf4 { -49.10/23 2.0s}
37... Qdc2+ { +M65/24 2.3s}  38. Kg4 { -49.62/25 6.1s}  38... Qb7 { +M21/24
11s}  39. Kh4 { -M22/19 1.7s}  39... Qh7+ { +M19/25 2.1s}  40. Bh5 { -M18/24
1.1s}  40... Qhe7+ { +M17/28 2.3s}  41. Kg3 { -M16/27 1.5s}  41... Qe1+ {
+M15/31 2.0s}  42. Qf2 { -M14/31 1.0s}  42... Qg7+ { +M13/34 2.2s}  43. Bg4 {
-M12/37 0.99s}  43... Qxf2+ { +M11/43 2.1s}  44. Kxf2 { -M10/81 0.97s}  44...
Qxg4 { +M9/100 1.9s}  45. Kf1 { -M8/120 0.11s}  45... d3 { +M7/120 0.065s}  46.
Kf2 { -M6/120 0.003s}  46... d2 { +M5/120 0.005s}  47. Ke3 { -M4/120 0.005s}
47... d1=Q { +M3/120 0.005s}  48. Kf2 { -M2/1 0s}  48... Qgg1# { Stockfish
261014 64-Stockfish 261014 64 2015.12.28}  ) ( 11. Qf4 { -3.84/25 32s}  11...
Qg6 { +4.39/25 34s}  12. Qf3 { -4.06/24 11s}  12... Qg5 { +4.56/25 24s}  13.
Qh1 { -4.46/24 24s}  13... Qf4+ { +4.89/22 5.7s}  14. Bf3 { -4.46/24 6.3s}
14... Kxd3 { +5.50/22 11s}  15. Qb1+ { -6.26/23 38s}  15... Nc2 { +5.89/23
8.6s}  16. Qb2 { -6.49/25 22s}  16... Qh4+ { +8.75/24 5.6s}  17. Kg1 { -8.89/25
13s}  17... Qg3+ { +10.73/25 7.8s}  18. Bg2 { -10.51/27 12s}  18... Kd2 {
+10.39/26 10s}  19. Kh1 { -7.77/26 5.5s}  19... Qh4+ { +12.27/25 15s}  20. Kg1
{ -11.33/23 8.0s}  20... d3 { +12.24/26 16s}  21. Bb7 { -16.35/28 50s}  21...
Qxc4 { +17.62/26 11s}  22. Kg2 { -16.58/25 13s}  22... Qd4 { +52.18/28 7.3s}
23. Qb1 { -31.53/27 31s}  23... Ne3+ { +M25/28 7.1s}  24. Kh1 { -M24/27 7.9s}
24... Qh4+ { +M21/31 6.2s}  25. Kg1 { -M22/1 0.001s}  25... Qg3+ { +M19/36
5.4s}  26. Kh1 { -M18/36 5.8s}  26... Ke2 { +M17/38 5.1s}  27. Qc1 { -M16/38
4.0s}  27... Qh4+ { +M15/41 5.5s}  28. Kg1 { -M16/1 0.001s}  28... Qf2+ {
+M13/49 6.0s}  29. Kh1 { -M14/1 0s}  29... d2 { +M11/70 5.2s}  30. Ba6+ {
-M10/81 5.7s}  30... Kf3 { +M9/120 0.47s}  31. Be2+ { -M8/120 0.40s}  31...
Qxe2 { +M7/120 0.007s}  32. Qg1 { -M6/120 0.005s}  32... d1=Q { +M5/120 0.005s}
 33. Qxd1 { -M4/120 0.002s}  33... Nxd1 { +M3/120 0.003s}  34. Kg1 { -M2/1 0s}
34... Qg2# { Stockfish 261014 64-Stockfish 261014 64 2015.12.28}  ) 11... Qd6 {
+3.95/24 20s}  12. Qh4 { -4.12/23 28s}  12... Qg6 { +4.53/24 61s}  13. Bf3 {
-4.00/23 6.4s}  13... Qxd3 { +4.83/24 54s}  14. Qh1 { -3.97/19 8.7s}  14... Nc2
{ +5.34/22 8.3s}  15. Qd1+ { -5.43/23 37s}  15... Kc3 { +5.34/1 0.001s}  16.
Qb1 { -10.45/27 29s}  16... Qxc4 { +5.94/21 7.7s}  17. Bg4 { -7.25/23 40s}
17... d3 { +6.90/21 5.2s}  18. Kg3 { -6.25/23 5.1s}  18... Qd4 { +7.42/22 10s}
19. Qa2 { -8.84/22 27s}  19... c4 { +8.15/24 17s}  20. Qa6 { -12.20/23 39s}
20... d2 { +15.03/23 33s}  21. Qa8 { -12.86/24 20s}  21... Kb2 { +11.22/20
7.5s}  22. Qb7+ { -14.57/23 12s}  22... Kc1 { +13.31/22 10s}  23. Qa8 {
-14.50/24 6.0s}  23... c3 { +15.70/24 18s}  24. Bf3 { -13.50/24 5.2s}  24...
Kb2 { +52.18/18 5.8s}  25. Kh3 { -52.11/19 6.0s}  25... Nb4 { +M47/22 13s}  26.
Qa4 { -M30/21 11s}  26... c2 { +M17/23 5.3s}  27. Qxc2+ { -M16/23 4.2s}  27...
Kxc2 { +M15/33 3.9s}  28. Bg4 { -M14/33 4.9s}  28... d1=Q { +M13/33 4.3s}  29.
Bxd1+ { -M12/53 3.6s}  29... Kxd1 { +M11/57 4.0s}  30. Kg2 { -M10/113 3.5s}
30... Qg4+ { +M9/120 3.7s}  31. Kf1 { -M8/120 0.12s}  31... Qh3+ { +M7/120
0.013s}  32. Kg1 { -M6/120 0.021s}  32... Nc2 { +M5/120 0.005s}  33. Kf2 {
-52.38/1 0s}  33... Ne3 { +M3/120 0.002s}  34. Kg1 { -M2/1 0s}  34... Qg2# {
+M1/120 0.002s, Black mates}   0-1

We can strongly(but not absolutely) believe that Black wins in this position.


Is there a single best move in every position?

No, there are positions in which a lot of moves have the same effect or are the same but you can play them in a different order.


Position where promotion to bishop is the only move?

There are numerous chess problems, whether a checkmating one or an endgame study, that feature certain promotions as a necessity to win. Stalemate is the long-known reason behind doing so. Here is a small sampling.
This problem is the first known one to use Bishop promotion, although it is a later correction. Even better it comes with double the fun!
[Titler "Ignazio Calvi  Le Palaméde 4/1836, White Wins (Correction)"]
[FEN "8/6PP/3Pn3/6b1/8/k3P3/p7/K2B4 w - - 0 1"]

1. g8=N! Bxe3 2. h8=B! (2. h8=Q? Nd4 3. Ne7 Nc2+ Bxc2 Bd4+ 5. Qxd4)    Nd4 3. Ne7 Bd2 4. Nd5 {And white wins!}

However, it can also be motivated by the "Dead Position" rule. In the below position, suppose White is down to seconds on the clock. They have no queens or rook nearby and stopping the clock to call in the arbiter might not help really. Thus, White must promote to a bishop, luckily just before the clock runs out. Now, the game is drawn and a half point is saved!
[FEN "8/3P4/8/8/8/7k/7b/7K w - - 0 1"]

1. d8=B


How do chess engines evaluate a position if the position is in the middle of an exchange?

A good chess engine won't stop after a predetermined number of moves, but will keep looking until the position is "quiescent", which roughly speaking means that there are no pending captures or checks. See Quiescence Search in chessprogramming wikispaces for a more detailed explanation.


These situations are very rare, but they do happen from time to time. An example is the following 1919 game between J.R. Capablanca (the future world champion) and F.D. Yates.

http://www.chessgames.com/perl/chessgame?gid=1055968

[FEN ""]
    [FEN ""]
1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Be7 6. Re1 b5 7. Bb3 d6 8. c3 Na5 9. Bc2 c5 10. d4 Qc7 11. Nbd2 Bg4 12. d5 g5 13. Nf1 h6 14. Ng3 Rd8 15. a4 b4 16. cxb4 cxb4 17. Bd3 Bc8 18. Be3 Ng4 19. Rc1 Qb8 20. Bd2 Qb6 21. Qe2 Nb3 22. Rc6 Qa5 23. Bxa6 Bd7 24. Bb5 Bxc6 25. Bxc6+ Kf8 26. Qc4 Nxd2 27. Nxd2 Qa7 28. Qe2 h5 29. Nf5 Bf6 30. Nc4 Qc5 31. b3 Nh6 32. Nxh6 Rxh6 33. Qe3 Rc8 34. Rc1 Bd8 35. Qxc5 dxc5 36. Nxe5 Ke7 37. Rxc5 f5 38. Rc4 Ba5 39. Bb5 Rxc4 40. Nxc4 Bc7 41. e5 Bb8 42. Ne3 Rh7 43. Nxf5+ Kf7 44. e6+ Kf6 45. e7 Rxe7 46. Nxe7 Kxe7 47. g3 Bc7 48. Kg2 Kd6 49. Be8 h4 50. Bf7 Ke5 51. Kh3 Bd8 52. Kg4 hxg3 53. fxg3 Kf6 54. Be6 Kg6 55. d6 Kf6 56. Bf5 Bb6 57. d7 Bd8 58. h4 gxh4 59. gxh4 Bc7 60. h5 Kg7 61. Be4 1-0

Black had what is called a "weak color complex" on the White squares. When White exchanged his rook for Black's white squared bishop, his white squares became very weak (because all his pawns were on Black squares. White was able to get his other pieces (a rook and knight) on white squares behind these pawns, and pick them off, while Black's pieces were bottled up on Black squares.


Does playing the King's Indian against the Benko put black at a foreseeable disadvantage?

No, there is nothing wrong with this approach for Black. A kingside fianchetto is a perfectly reasonable response to White's. You are likely to end up transposing to an actual King's Indian if White eventually plays c4, in which White's fianchetto is a fine setup but not a killer.


Why do chess tournaments award so many points for a draw?

I don't see how tournaments incentivize people to go for a draw. You literally cannot win any tournaments by drawing every game.
Yes sometimes there are draws that are clearly prearranged but other than that only bad players say draws are bad for chess. The funny thing is that these low rated players are usually not getting draws even against similar strength opposition. They also can't figure out what's going on in high rated games without an engine.
The issue being your football system is it would change the elo system and encourage win trading. The best way to gain elo would be win farming against much weaker opponents, as you would lose elo drawing against people of similar elo. The players with the highest elo would not be participating in these super tournaments to maintain their elo. Also colluding draws is nowhere near as damaging as win trading in this system, as the tournament winner cannot really win by drawing every game, but can easily win winning 50% and losing 50% of his games. Also it is freelo due to 1 win and 1 loss against a similar rated opponent being a net gain in elo.


How many points is each chess piece worth?

The answer by MikroDel gives the commonly-used "Reinfeld values" of pawn=1, bishop=knight=3, rook=5, and queen=9 (kings are essentially worth an infinite number of points, because the game ends if it is lost). While this is a good guide, chess is rarely that simple. Many books will give the value of bishops as 3.5 instead of 3, simply because they are often much stronger than knights in endgames and open middle-games.
There are other things to take into account as well. For example, bishops are much stronger if you own both of yours, but you opponent has already lost/traded one or both of theirs. The nature of the position can also affect the worth of individual pieces, as a position that is completely blocked up might leave a bishop with no useful squares to go to while a knight may be able to jump straight over the obstruction.
Another example of how the Reinfeld values can be misleading is that 3 minor pieces (bishops and knights) are often more powerful than a single queen, provided that they are used properly.
For some further reading, you might also want to take a look at http://en.wikipedia.org/wiki/Chess_piece_relative_value which has a much more detailed explanation.


Wrongly accepted stalemate but game is a clear win?

According to the FIDE Laws of Chess:

  5.2.3  The game is drawn upon agreement between the two players during the game, provided both players have made at least one move. This immediately ends the game.

However, the annotations to rule 5.1.1 state:

  Particularly in junior tournaments it can be discovered that one player accepts he was mated to discover later that he could prevent the mate.  If a result is reported by both players that can be accepted.  Where a player announces mate and immediately shakes hands only for it to be discovered seconds later that the move played was not mate he should not be given the win despite any handshake.

I would tend to think that a false stalemate should be handled like a false checkmate, and the game should be resumed if the error was discovered within seconds.


Why does a chess engine not get excited about a piece exchange at the end of its analysis depth?

Chess engines will always try to extend the search by a few moves, so a position is only evaluated if it is considered "quiet". This is called Quiescence Search, and the problem you describe that it is trying to prevent is called the "Horizon effect".
So before evaluating a position, if there are captures, checks and so on in the position, then the search is first extended by those moves.


Why is King's Gambit said to be refuted?

We all known that Bobby Fischer has published the famous "A Bust to The King's Gambit", where the gambit is said to be losing for white. Why is it so? Is there any line that can secure black an advantage in the opening, assuming best play from white?

It is not refuted but the Modern variation is very "pleasant" for Black at the moment, even though being "equal". The fact is that White barely holds equality here, and if he makes the slightest mistake then chances are high for him to lose the game. I am referring to the line 1.e4 e5 2.f4 exf4 3.Nf3 d5! 4.exd5.

Other old popular lines are very sharp and unexplored but mainly easier to play with Black. I refer to the lines where Black plays ...g5 with Black's dark squared bishop being posted on d6 or g7. These are simply ultra sharp, inhuman lines where even computers explode!

That is the reason why you will not see King's Gambit being played at the top/master level:

Too much memorization of lines which can be refuted by one computer-like novelty;
Even if White manages to get out of the opening with "equal" position, Black usually has easier time playing the middlegame;

I have checked the evaluations of all the lines in the Chess Informant ECO ( 2006 ) and my claims are supported -> White will always have a move that offers equal / sharp game, but the positions are wild and very hard to play.

This is not something that top GMs want, they do not enter into highly tactical lines.

The reason for this is that in order to play this type of chess, you need to be physically very fit, you need to solve puzzles on a daily basis, you lose a lot of energy over the board when playing like this ( this is very dangerous for tournament play because you will play subsequent games worse ), the amount of stress you suffer is very high, and most of the time the entire line can be refuted by a single novelty found by a computer. Furthermore, the openings like this reduce to "I calculate better than you" type of game, so GM can not defeat markedly weaker player if he prepared his opening and calculates as good as that GM ( I have seen players who "fit this bill" so it is not impossible ).

If you intend to play King's Gambit as White, or you play 1...e5 by all means get John Shaw-King's Gambit ( 2013 ) as it is most up-to-date publication and the coverage is simply exceptional.

I wish I could give you some illustrative lines but the material is so vast that it would not fit in 10 posts or even more! Just get the book and all will be clear!

Best regards.


If all the pieces are on the board, there are 64!/32!/8!^2/2^6*(32/63)*(31/61) or about 1.2*10^42 positions.  This would require 140 bits.  The 64!/32! puts the pieces on squares, the divisions account for permuting like pieces, and the last two fractions put the bishop pairs on opposite color squares.  I would guess a dozen or so more bits would be required to cover positions with some of the pieces gone, but calculating the exact number is not so easy.  Decoding a position from 140 bits can be done, but would be a pain.  Clearly 8 bytes will not suffice.


When was the oldest person ever to have a FIDE rating born?

I've no proof him to be the earliest born of them all, but after browsing the earliest FIDE rating lists, my candidate would be Esteban Canal:

Born in 1896, April the 19th, the Peruvian master was 75 when he entered the first published list in July 1971 with an Elo of 2270.

He beats grandmaster Friedrich Saemisch by five months.


(4 Queens + 3 Pawns) vs (Entire Standard Army)

A clarifying comment says "Pawns can be placed in any of the first 3 rows.
Any other piece must be placed in the back row. White moves first unless
black used less points to construct their army."  So the position I gave
earlier doesn't work, but since Black is allowed to move first with fewer than
39 points there's still a forced win:

[FEN "1b1qkqq1/8/8/8/8/8/PPPPPPPP/RNBQKBNR b - - 0 0"]

1. Qxf2+ Kxf2
2. Qh4+ g3
3. Qgxg3+ hxg3
4. Qxg3#


Well for 1.d4, White's able to win a pawn outright with 2.Bxg5. In 1.e4, the extra tempo gives White better chances to capitalize on Black's dubious move.


How is time measured when a player is late?

Play starts when the arbiter announces the start of play, usually by saying "Start white's clock". A good arbiter will then walk round the tournament room making sure that all clocks have been started. If both players have yet to arrive at a table then the arbiter will start white's clock. If a black player has not started white's clock then the arbiter will do so and make a mental note to check back and make sure the black player doesn't stop them again as this could lead to the round finishing late.
If a player with the white pieces arrives late, therefore, then when they arrive they will have lost the time from the start of the round when the clocks were started. If the black player was on time then this will be when the black player started the clock. Otherwise it will be when the arbiter started the clock.
If a player with the black pieces arrives late then when they arrive they will have lost the amount of time since clocks were started minus the amount of time white used for the first move.
If the default time is, say, 30 minutes, then the arbiter will go round the room looking for empty seats with a clock with 30 minutes gone. This works for absent white players and for most black players. The exception is when David Howell is white and has taken 10 minutes for his first move.


Is there fiction dealing with retrograde chess analysis?

There's also A Happy Solution by Raymond Allen.  It's a short story (under 6000 words), but quaint. It appeared in The Strand Magazine in 1916.
The puzzle featured in Allen's tale was posted here in Chess.com's forums:
[FEN "2BK3N/NP1P1PPb/P4P2/3p1q2/1Q1P1b2/1pB1p1p1/p1p2pp1/1kr4r w - - 0 1"]

While Chess.com's puzzle is set up for Black to force mate, it is also the board that Kenneth Dale did a retrograde analysis on.  The game was between Sir James Winslay and Lord Churt.  When a banknote was found to have been pilfered, Churt's secretary Gornay was remembered to have been watching the game, but no one could vouch for how long.  Gornay's innocence appeared inviolate, as he was also remembered to have made several remarks on some of the past moves of the game at its conclusion:

"If the play was rather eccentric sometimes, I must say it was bold and dashing enough on both sides," Gornay commented. "For instance, when Lord Churt gave up his knight for nothing, and when you gave him the choice of taking your queen with either of two pawns at your queen's knight's sixth." He turned to Churt. "Possibly you might have done better to take the queen with the bishop's pawn instead of with the rook's."

After this, the missing note was found in the wrong envelope, and Dale suspected that Gornay may have been the one who had moved the note, in order to frame Dale in case of the note's being found.

"Was he in the library all the time you were playing?" Kenneth asked.
"I can't say that," Churt replied. "I don't think he was. I didn't notice particularly. But I am positive that he did not enter or leave the room while I was standing looking at Winslade's move, and he must have been there when Winslade offered his queen and when I took it, because he was commenting on those very moves after the game was finished, and suggesting that I might have done better to take with the other pawn. You heard him yourself."

Dale later proved that Gornay could have figured out those previous moves simply by looking at the resigned game, and therefore had been free to leave the room and do his dirty work while the game was still underway.


A couple of suggestions:

Solve chess puzzles daily. Use 'mate in two' puzzles (also called combinations) only. 'Mate in three' is usually more complicated and requires more time/energy and is less emotionally satisfactory (you may lose interest).
Note: in classical (which you should use) 'mate in two' puzzles a. first move is never a check b. rarely a capture
Analyze openings as well. I think that ending is a good thing to study. But what is the use of it if you cannot get to ending without proper knowledge of openings?
I would suggest to especially focus on opening tricks, because at your level many people may try to apply them (use simple logic: it's easier to 'catch' a beginner than an advanced player)
I would suggest study 1.e4 openings for white (open)
For black you may choose 1. ... e5 (the 'classic' response) however 1. ... c5 (Sicilian) 1. ... e6 (French) and other 'main-stream' responses are good as well.
Every time analyze games that you played. Try to find either a club with a coach, find a coach on the internet, ask your friend or... simply do it yourself (if no other options available).
All leading chess players advanced mainly by analysis of their mistakes.
Analyze games of leading chess players: Kasparov, Karpov, Steinitz, Lasker, Capablanca, Alekhine, Botvinnik and etc. etc. This you can do on your own or with a coach. In fact, I would suggest to analyze them on your own by reading comments to the moves (usually comments are made by other leading players)
Play regularly. If you can't play in tournaments, play online. ICC (Internet Chess Club) is a great choice (I play there a lot for many years)

I hope it helps!


I agree with the previously-given answer from Matthew Liu (please give it the checkmark), but I’ll add the standard notation of the solutions since you ask:

1.f3 e5 2.g4 Qh4#

1.f3 e6 2.g4 Qh4#

1.f4 e5 2.g4 Qh4#

1.f4 e6 2.g4 Qh4#

1.g4 e5 2.f3 Qh4#

1.g4 e6 2.f3 Qh4#

1.g4 e5 2.f4 Qh4#

1.g4 e6 2.f4 Qh4#


Would certain checkmates be possible if the king could move into check?

You could force a checkmate with two knights and a "king". Because the "king" does not fear being taken, it can move directly in front of the opponent's king, if it is protected by a knight.  All it has to do is do this when the opponent's king is on the side of the board and thus cannot retreat - and it is known that two knights and a normal king can force the opponent's king to the side of the board.

Based on trying it out, I believe a "king" and single knight could also force checkmate. The knight supports the "king" very well, cutting off squares and proving good places for the "king" to advance. And when the knight retreats, the "king" is usually ready to go into that same square if necessary, cutting off the king and forcing it backwards.

With a bishop and a "king", I think the question is whether the king can be forced into a corner which is the same color as the bishop. The following position, with either side to move, results in a quick checkmate, because Black must go into the corner:

[FEN "1k6/8/1K2B3/8/8/8/8/8 b - - 0 1"]

I believe this can't be done from many positions, though.  From most positions, the king escapes into the wrong corner. Although it can be driven from that corner, it can then flee to the wrong corner on the opposite side of the board.


Smallfish as mentioned is good, the website lichess.org has made an app, you can downnload it and make an account. It needs internet connection for the database but not for the complete game analysis


How to write an interface to lichess for a millenium board using chesslink?

As you've seen, the Lichess API only allows bots to use the API functions that make moves in an ongoing game.  As far as I can tell, this is intentional; the API requires that anything that can generate moves in a game by some means other than human interaction on the Lichess site must be flagged as a bot.

Which means (again, as far as I can tell...), the only way to do what you want to do would be to create some kind of intermediary between the e-board and Lichess that actually mimics the actions a human would take during a game (such as simulating mouse clicking and movement on a game's web page).

I personally would not know where to start if I were trying to do this, and I also don't know if doing something like this would trip Lichess's anti-cheating detection in any way.  But it appears that this is what you'd have to do in order to play on Lichess using an e-board.


Term for checkmate where every participating piece attacks exactly one square around king

As a problemist, I can assure you that the term as such does not exist in problem language. Bohemian school did only know three concepts: pure mate, economic mate (all pieces - but not necessarily king or pawns - participate) and both at the same time.
Yet, not all hope is lost. At least one Bohemian troll had the following idea: What is the most uneconomic economic mate? Well, obviously one where each white piece idles as much as possible, i.e. guards only one flight, i.e. exactly which you describe. I don't remember the position offhand, but I'm fairly sure "the swarm" could dig it up if I take your request to a specialist forum. I edit it in if I can come up with it and you are interested, but don't expect that its historical solution comments contain the "Oh, look, an XYZ mate!" notion you seek.


How do you have Arena show the second and third best move in analysis?

Right click on the analysis output window to be able to enable Multi-PV mode:


Najdorf Variation: strategy after taking poisoned pawn?

It would be strange it it were possible to give a short list of pitfalls for one of the most complicated variations in chess. I'll try to give some hints, I don't play it from either side but I'm an opening nut.

First, you've chosen to include 10.e5 dxe5 11.fxe5 but the interesting position is the one after 9...Qa3, where black has chosen to accept the so-called Poisoned Pawn. The other really big main line is 10.f5, and the strategy is similar (white tries to checkmate black).

Also first, the current big fashion for black is to play 7...h6 8.Bh4 before playing 8...Qb6. So if you're looking for recent games, look for games with that included as well.

In the position after 9...Qa3, white has a huge lead of development. Black has an extra pawn and the better pawn structure. Fundamental Chess Openings says "It is in fact very attractive for White to offer this pawn, and it is equally attractive for Black to take it. An ideal setting for a ferocious fight!"

White's strategy is to go all-out to checkmate black's king, as he's burned his bridges already. Black's strategy is to survive the onslaught and somehow return to a normal position (develop his pieces, return his queen to a more normal square) and if he manages that, he'll often be winning. Theoretically, chess is of course a draw, which means here that many of the long, long calculated out lines end up with white having just enough attack to give perpetual check, but not checkmate.

An example from FCO:

[FEN ""]

1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bg5 e6 7.f4 Qb6 8.Qd2 Qxb2
9.Rb1 Qa3 10.f5 Nc6 11.fxe6 fxe6 12.Nxc6 bxc6 { Now comes a second pawn sacrifice
to speed things up } 13.e5 dxe5 14.Bxf6 gxf6 15.Ne4 { This is the starting point of
variations, based on themes like } 15... Be7 16.Be2 h5 17.Rb3 Qa4 18.Nxf6!? Bxf6
19.c4

"It seems incredible that White should have sufficient compensation for the great
material sacrifices he has made, but Black's position is extremely uncoordinated and
his king has no safe place anywhere on the board. According to the present state of
opening theory, attack and defence are equally balanced, but... everyone is holding their
breath for future developments."

Here's Radjabov-Karjakin (1-0) from 2006 that helped make 10.e5 be the most popular line for a few years again (source: http://www.chessgames.com/perl/chessgame?gid=1433642)

[FEN ""]
[Event "Cap D'Agde"]
[Site "Cap d'Agde FRA"]
[Date "2006.11.02"]
[EventDate "2006.10.30"]
[Round "3.2"]
[Result "1-0"]
[White "Teimour Radjabov"]
[Black "Sergey Karjakin"]
[ECO "B97"]
[WhiteElo "2729"]
[BlackElo "2672"]
[PlyCount "65"]

1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6
7. f4 Qb6 8. Qd2 Qxb2 9. Rb1 Qa3 10. e5 dxe5 11. fxe5 Nfd7
12. Ne4 h6 13. Bh4 Qxa2 14. Rd1 Qb2 15. Qe3 Bc5 16. Be2 Nc6
17. c3 (17.Nxe6!! { White could have played this } Qb4+ {forced} 18.c3 Bxe3 19.Nc7+ Kf8 20.cxb4 Rb8 21.Bg3 {with the threat of e6}) Qa3 18. O-O O-O 19. Nf6+ Nxf6 20. Bxf6 Nxd4 21. Rxd4
Bxd4 22. Qxd4 gxf6 23. exf6 Qa5 24. h4 Kh7 25. Bd3+ Qf5
26. Re1 Rg8 27. Kh2 a5 28. g4 Qxd3 29. Qxd3+ Kh8 30. Re5 Rxg4
31. Rh5 Rg6 32. Qd8+ Kh7 33. Qe7 1-0

Here's a Stellwagen-Anand, 0-1 in 2009, in the 10.e5 variation. The early queen sacrifice is long-known theory, technically 17...Ra4!? is the first new move of the game but it's unclear how much was preparation. 38...Kb8?? could have thrown away the game to 39.h6!, later 46.h6?? is also a blunder.

[FEN ""]
[Event "2008-2009 Bundesliga"]
[Site "Baden Baden GER"]
[Date "2009.03.28"]
[EventDate "2008.10.03"]
[Round "14"]
[Result "0-1"]
[White "Daniel Stellwagen"]
[Black "Viswanathan Anand"]
[ECO "B97"]
[WhiteElo "2605"]
[BlackElo "2783"]
[PlyCount "104"]

1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6
7. f4 Qb6 8. Qd2 Qxb2 9. Rb1 Qa3 10. e5 dxe5 11. fxe5 Nfd7
12. Ne4 h6 13. Bb5 axb5 14. Nxb5 hxg5 15. Nxa3 Rxa3 16. O-O
Nc6 17. Rb5 Ra4 18. Nxg5 Ndxe5 19. Rxe5 Nxe5 20. Qc3 Nc6
21. Rxf7 Ra5 22. Rxg7 Bc5+ 23. Kh1 Rf8 24. Qd3 Rxa2 25. h4
Ra1+ 26. Kh2 Bd4 27. Qg6+ Kd8 28. Rf7 Rxf7 29. Qxf7 Bg1+
30. Kg3 e5 31. h5 Nd4 32. Qf6+ Kc7 33. Qxe5+ Kb6 34. Qd6+ Ka7
35. Qc5+ Kb8 36. Qd6+ Ka8 37. Qd8 Nf5+ 38. Kh3 Kb8 39. Ne6
Ra3+ 40. Kg4 Nh6+ 41. Kf4 Bh2+ 42. Ke4 Nf7 43. Qf8 Nd6+
44. Kd4 Ka7 45. Nc5 Ra5 46. h6 Bg1+ 47. Kd3 Bf5+ 48. Qxf5 Nxf5
49. h7 Ra3+ 50. Nb3 Bd4 51. Ke4 Bh8 52. Kxf5 Ra2 0-1

Edit: crap, I didn't realize the PGN viewer doesn't show comments. I only had a few, but they don't show, sorry.


The New Art of Defense in Chess vs The Art Defense in Chess

Yes, the new book is quite different to the old one:

  On the whole, however, The New Art of Defense in Chess should be seen as a fundamentally new book. This is because Soltis recognizes the way in which dynamism and activity have become fundamental to modern defensive techniques.

Source: ChessBookReviews, emphasis is mine.

Synthesising the review, the reasons why the book is different is because:

Computer analysis has helped players find flaws in the attack in postmortems, which they use to improve their defensive technique
Players are more open to playing 'ugly', counter intuitive moves that are based on concrete analysis
After Tal's reign as world champion, players realised that active defensive is usually better than passive defence


Guidelines for chess tournament prize distribution

The US Chess Federation Official Rules of Chess 5th Edition has a section (section 33, if you have a copy) that has some guidelines about prizes.  These are specifically described as recommendations and not rules.

A ratio of 10 to 1 between the top prize and the entry fee for serious tournaments is suggested (and perhaps even more if you want to attract top players.)

It suggests that class prizes be at least the amount of the entry fee, and also suggests that the place prizes all be higher than the class prizes.


Tool for solving puzzles with multiple defense lines, alternative solutions and playing wrong lines until user resigns

This sounds like just playing the original position against an engine normally, except maybe with a "correct move" message whenever the correct solution moves are played, and "you solved it" at the end?

I "play out" Shredder's puzzles sometimes this way by switching off puzzle mode and backing up a move. But yeah, it's clunky (a lot of extra clicking) and should be easier.


Czechoslovakian Master Karel Prucha formulated some correct principles on how to play the Albin Counter Gambit and published them in Ceskoslovensky Sach 9/1962:

1. The Albin is playable only if it is treated as a pure gambit.
   Black should not try to regain the pawn by attacking White's e5-pawn,
   but must continue in gambit style with ...f7-f6.

2. After that, Black must castle short. Long castling leads to mutual attacks where
   White's extra pawn becomes a factor.

3. Black should keep the d4-pawn at any cost.

4. Black's Queen should be posted on d7 with the idea of exchanging of the
   light-squared Bishops by ...Bh3 and enabling additional support for the
   d4-pawn by ...Rad8.

5. It is best to place the dark-squared Bishop on c5, which means that if White plays
   a2-a3, then a7-a5 is necessary to stop White's advance b2-b4.


Why does Stockfish lose against this piece sacrifice in the Berlin Defense?

Is it due to the limited strength of the featured Lichess engine?

Most probably it is the above.
Using the engine at lichess.org/analysis (which is Stockfish 13 NNUE, almost the newest version of Stockfish available), on move 20 its eval was -5.9 for Black and it recommended 20...Rxe1+. The move played, 20...Be6, cost Black a significant amount of its advantage (the eval dropped to -2.8), and 21...Bf5 caused another similar drop. In my analysis run, Stockfish 13 NNUE realized Black had lost its advantage as early as 24...Rf8 (0.00 eval). All the above analysis was at rather low depth of ~25, taking only a few seconds to evaluate for me.
I can't tell if JS used Stockfish 12 with NNUE on. If he didn't, it is over a hundred elo weaker than Stockfish 13 NNUE. I note as well that the analysis engine only ran to depth ~16 at most, which is a very shallow depth in engine chess today (it corresponds to searching only ~8 moves ahead - even human GMs can search further than that in some positions).


How many female players participated in the european indivdual championship?

You can find the final rankings here to get a list of all participants. You could then check the names against the FIDE ratings website which would tell you the gender of the player.

A quick glance through the list shows these additional female players (probably not exhaustive)

Shlomit Vardi

Limor Altshul

Sophia Toporkova

Michal Lahav


What is White's objective from this state?

White needs to put his bishop on f6 in order to create winning chances, so a good way to start is by playing f3, planning Be1-h4-f6, followed by Qf2, with two ideas: either Qh4, Rg5-h5 (possibly with Rdg1 first if necessary), or Rg3-h3, then Rxh7, with mate in either case.

The first question is whether black can defend against this by moving his king to the queenside, and playing h5 at the right moment. But a more important question (as the former is a best case scenario in which white cannot lose) is whether black's counterattack on the queenside with b6 and a5 or c5 may end with white getting mated (as white's plan is slow, whereas black's counterattack is quick, though mate is not obvious).

But in any case, with the white pieces, you must realise that lines will be opened on the queenside, so black can also play for a win. The only reason why white may claim an advantage in this position is because his bishop may potentially have a future over black's, but this isn't necessarily true if black can find a good square for his bishop if and when he plays c5 and d4.

So f3 and manoeuvring the bishop to f6 is white's only way to win; black has the option of defending or counterattacking. Conversely, white can attempt to establish a grip on the dark squares by playing Be3 and c3, and try to hold the position to a draw, but this seems unlikely as black will be able to crash through.

Long story short: white's plan as described is practically forced, but whether he will win or not is a different story.


Why was 5...Nf6 traditionally preferred to 5...e6 in the Two Knights Caro-Kann?

After 5....Nf6 6.d4 dxe4 7.Nxe4 Qxd4 (1), 8.Bd3 seems the only move for white to prove he has enough compensation for the pawn. Now black has two good options: 8....Nbd7 or 8....Nxe4 9.Bxe4 Nd7.

After 5....e6 6.d4 dxe4 7.Nxe4 Qxd4 (2), white has more options. He can play 8.Bd3, but also 8.c3! is a popular option.

In terms of objective evaluation, both variants probably don't differ much, but black should have less problems in (1) compared to (2).

Should black play 5....Nf6 or 5....e6? Difficult to say.
According to the Game Database of ChessTempo, the latter is more popular, but, after white's most popular answer 6.d3, both moves often transpose. On the other hand, after 5....e6, black keeps the option to develop with g6, Bg7, Ne7.

      [FEN ""]
      [StartPly "9"]

      1.e4 c6 2.Nf3 d5 3.Nc3 Bg4 4.h3 Bxf3 5.Qxf3 Nf6 (5...e6 6.d4 (6.d3) dxe4 7.Nxe4 Qxd4 8.c3 (8.Bd3)) 6.d4 (6.d3) dxe4 7.Nxe4 Qxd4 8.Bd3 Nxe4 (8...Nbd7) 9.Bxe4 Nd7


The International Master Gary Lane in his book about the Vienna game wrote in 2000 that this opening "has a long history and a bright future". He added

"in these days of computer databases [already 20 years ago!], opening
theory has become so intense that some variations have been analyzed
to move 30. It is hardly surprising that some 'forgotten' opening
variations have been revived by players to looking into unknown
territory, and the Vienna is a perfect arena for this."

So, if Vienna suits you, if you like the obtained positions, if you know the main theme (e.g. which pieces to swap, which promising pawn structure to get, ...) go ahead!
Here are some stats about the Vienna game compared to others openings in a Big and a Masters database. In the Big one, the Vienna game is the second choice and compared to 2.Nf3 it offers a higher risk (more losses) but also a premium (more gains). The Vienna is the 3rd choice in the Masters database with also a higher variance.

In the Big database

In the Masters database


How did classic masters like Alekhine and Anderssen practice tactics?

In Joosep Grents's wonderful biography on Paul Keres, there is a brief first-hand account of tactics training in that time period. For background, Paul was a contemporary of Alekhine and almost played him for the World Champion title, but the match never materialized.
Here's what Paul Keres had to say about training tactics in the 1930s (emphasis mine):

I used correspondence games, above all, for experimental purposes,
often opting for very risky opening lines and attempting, at all cost,
to create complicated positions which I could use to train my tactical
skills... It is easy to notice a bias toward tactics in these games,
while there are still considerable problems apparent in solving
strictly technical problems.

The article notes that at one time Paul was playing more than 100 correspondence games at once.


How should I deal with two siblings in the same section?

The situation is not very different to two training partners or two friends being paired. The dilemma between sportsmanship and friendship is the same. Are you allowed to "misuse" personal information about weaknesses of your opponent? Should you pre-arrange a result to fit the needs of each other?

The keyword is sportsmanship here. You are playing in a chess tournament because you like the thrill of a tournament, the competition and over everything else: the game. You both share this love. Why should you sacrifice the idea of the sport at all? Trying to win against an opponent is not a personal affair, but a trial of strength between the two players. That is why you joined the tournament in the first place! If someone beats me, he might still be my best friend (at least, after my embarrassment of having lost is gone). If you pre-arrange a game, you harm the idea of the tournament and you harm yourself, because you get less excitement and benefits from playing there.

There are several cases of successful siblings competing in the same sport at the highest level. In Formula 1, the Schumacher siblings Ralf and Michael were competing for several years at the same races. In woman chess, the Kosintseva siblings Tatiana and Nadezhda are both ranked among the 20 strongest women. I think they attend the same tournament together very often. I doubt any of them would sacrifice the sport, nor did I ever hear someone voicing that opinion.

Hence I would suggest, the more professional the level of play is, the less you have to worry about siblings being paired against each other. As a tournament director my fear about cheating players would not increase only because there are siblings playing.


Chess isn't popular because all major tournaments make it lack emotion.  For some reason, all major tournaments are those of classic chess, that is, with high quality games that last 5 hours or more.  The outcome of these high quality games at the highest play level is most typically a draw.  This is totally broken and does not have a chance to make it to the mainstream public.

Now look at soccer, which has a bit of popularity in Europe and South America.  At the higher level there are few goals scored but games are more often than not full of emotion.  Just like chess, a small mistake (even a referee mistake) can determine the result of a game.  Just like chess, it is a game of mistakes, but there is a major difference: things happen fast, sometimes faster than the eye can tell. The center back does not let the forward to think as much time as he wishes so that he can make the shoot of the century. Instead, he tackles him.  The difference of level among a division and the division below is the time they have left to make a decision once they have the ball.  The higher the division, the shorter the time to think.

To answer your question, FIDE does not try to make chess more popular because it is promoting the classic games, which are of no interest and of a lot less quality than two machines playing against each other with a regular computer.  FIDE has been losing time trying to make chess an Olympic sport so that it can get funds by governments that are willing to increase their vanity each 4 years by getting Olympic medals.

If FIDE had any interest in making it more popular, the major tournaments where all money and fame are need to be of fast games, from 5 to 10 minutes by player, with lower quality but a lot more fun, and leave the perfect games for the machines.


Ranking systems that take into account the size of the victory

If you're interested in use (more than in development), you should give a try to rankade, our ranking system that features rankings, stats, and more.

Rankade doesn't use Elo, but its algorithm (called ree algorithm), although more complex, is similar to Elo if you play 1-on-1 matches only.

Opposite to Elo and Glicko  (here's a comparison), rankade can manage any kind of match (one-on-one, faction vs. faction (two teams, which may be asymmetrical),
multiplayer, multi-faction, cooperative games, single player games, and so on), so you can insert one match with Alice 5, Bob 4, Chris 3 output (without breaking down one actual match in multiple fake matches). Anyway, rankade - like all aforementioned ranking systems - does not incorporate margin of victory (even if you can easily manage this issue using weight feature, and/or insert scores for stats).


How to draw this rook and pawn vs. rook endgame?

In your diagram/game, black is allowed to set up a Lucena position and therefore wins. However, with correct way of harassing the black king, it is possible to prevent that from happening. After 2... Kc5, you can utilize what's called a frontal defense by playing 3. Rg1. In the lines shown below, black simply cannot proceed.

Note, that this defense may or may not work depending on which line and how advanced the opponents pawn is - see reference below.

3r4/6R1/2p5/2k5/8/4K3/8/8 w - - 0 2

1. Rg1 Kb4 2. Rb1+ Kc4 (2... Ka4 3. Ra1+ Kb3 4. Rc1 Rc8 5. Kd4 (5... Rd8+ 6. Kc5=) Kb4 6. Rb1+=) 3. Rc1+ Kb5 4. Rb1+=

If black moves his rook away from d-file in attempt to block your checks or harass your king, then you can bring your king in front of the pawn and set up a 3rd rank defense - Philidor position or a back rank defense (depending on how the game develops).

Also, this wiki page gives an excellent quick overview of R+P vs R endings.


Chess engine with an ELO of less than 1800

Take a look at numpty. It claims to have a ELO of about 1500-1800. I've played it on FICS before and it usually has a blitz rating of 1900-2100. Note that FICS ratings are usually horribly skewed by all the cheating that happens on there.


There’s no reason for you to scale down your engine doors if it’s fast. Why would you do that?

I am sure Talkchess used to have a post about how chess engines report searched nodes differently. I can’t find it now it was a few years ago. Read it before... their search function is not good.

If you are interested in the difference you will need to read the SF source make sure how they increment the node counter is consistent to yours. Also you may want to test SF on your own machine.


Can anyone give good primary resources on Deep Blue?

One place to look is the Computer History Museum in Mountain View, California. Some of the hardware is there (but it's not very interesting). More important, though, is that you can do a site search that gives a fairly long list of articles.


Can a pawn that performed an en passant capture promote at all?

From FIDE rules (3.7 e):

  When a pawn reaches the rank furthest from its starting position it must be exchanged as part of the same move on the same square for a new queen, rook, bishop or knight of the same colour. The player’s choice is not restricted to pieces that have been captured previously. This exchange of a pawn for another piece is called ‘promotion’ and the effect of the new piece is immediate.

There is no restrictions whatsoever about capturing en passant.


White is threatening to take the pawn on e5. It couldn't take it with 5.Nxe5 because, since the pawn on d4 is undefended, Black can immediately get it back with ...Qd4 6.Nf3 Qxe4+. Or Black could also consider ...Qg5 followed by ...Qxg2. With 5.Nc3, the e4 pawn is defended, making the threat of taking on e5 more serious. If you look at games between highly rated players, 5...f6 is indeed the most popular move, but there are other alternatives that are also fairly frequent, such as ...Qd6 and ...Bd6. I'm pasting below the table from the lichess opening book. If you look at all the popular moves (say those with more than 10 games), they all defend the pawn one way or another (in the case of 5...Bc5 it is a bit tactical).

That said, I don't know why defending with ...f6 is the most popular. It is simple and solid, I suppose (maybe they prefer to defend a pawn with a pawn to give more freedom to the pieces?). If you go by results, protecting the pawn with the queen or bishop (the second and third choices above) are also fairly common moves and actually have a higher frequency of wins for Black (but also for White!).


A deceptively simple eight piece endgame

No need for engine analysis, that's a win for White since that parciular a+c pawn endgame is won. White can simply trade the other two pawns with Rh6


Is this endgame drawn after the rook sacrifice?

Let's note the following: 1.Rxc2 and 1.Kxf4 and 1.Rd8+ are equally good, since they all draw. If we ignore 1.Rd8+ for now, 1.Rxc2 is clearly at least as good as 1.Kxf4 in the position, since it drives black's king back one square, meaning that black will at some point have to 'waste' a move with the king to get to white's remaining pawns (the option of 1.Rd8+ introduces a different way for black to play for a win that ultimately doesn't work, but needs to be taken into consideration. This line should be considered if we come to the conclusion that 1.Rxc2 loses by force).
So we begin by calculating a few steps ahead in the 1.Rxc2 line (since it's a direct capture, and if it works then we're happy): 1...Kxc2 2.Kxf4 Kd3 (this is why 1.Kxf4 and 1.Rxc2 are equally good; it doesn't matter if black's rook is on c1 or on b1).
This will be the main tabya of the endgame, and at this point white needs to make a decision: which pawn should be used as the main passer?
Let's consider our options, beginning with the h-pawn:
[White "NN"]
[Black "NN"]
[FEN "8/8/8/8/4PK1P/3k4/5P2/1r6 w - - 0 3"]

3.h5?? Rh1 4.Kg5 Kxe4 5.f4 (5.Kg6 Ke5 {White's king is chained to the h-pawn.} 6.h6 Ke6 {Opposition. Now Black threatens to play ...Rg1+, forcing White's king onto the h-file, and granting access to the f-file for Black's king.} 7.h7 Rg1+ 8.Kh6 Kf7 9.h8=N+ Kf6 10.Kh7 Rg7+! {All that is left to ensure victory for Black is to round up the final pawn.} 11.Kh6 Rg2! 12.Kh7 Rxf2-+ {With the knight in the corner, White is helpless.}) Kd5! {The way black wins in this position is to maneouver their king to the f-file, where it will be able to contain both of white's passers. Since the black rook keeps White's pawns from advancing too quickly, Black will be able to interfere with the king in time.} (5...Rg1+ 6.Kf6 Kxf4?? 7.h6= {and White's pawn promotes.}) 6.Kg6 Ke6 {Black is now threatening to play ...Rg1+, after which Black's king reaches the f-file} 7.f5+ Ke7 8.f6+ Kf8-+ {Black will now be able to either pick off White's two pawns, or White's king will be caught in a mating net.}

So the h-pawn is a no-go. What about the e-pawn?
[White "NN"]
[Black "NN"]
[FEN "8/8/8/8/4PK1P/3k4/5P2/1r6 w - - 0 3"]

3.e5?? Kd4! {The problem with the e5 push is that it allows Black's king easy access to the d5 square, which makes it impossible for White to gain enough time for the pawns to advance successfully.} 4.Kf5 (4.e6 Kd5 5.e7 Re1 {just drops the pawn.}) Kd5 5.f4 Rh1! {luring White's king away from the e6 square, creating access for Black's king.} 6.Kg5 Ke6-+ {Again, White will not be able to stop Black's king from getting to the f-file, after which Black will either mate White's king or pick up the passed pawns one by one.}

Ok, only one attempt left to consider then!
[White "NN"]
[Black "NN"]
[FEN "8/8/8/8/4PK1P/3k4/5P2/1r6 w - - 0 3"]

3.Kf5! {This is the only way to draw, and it is by far the best move in the   position. White waits with pushing a pawn forward until after Black has made a  commitment which leaves White with a tempo to spare in comparison with many of the previous lines, i.e. the answer to the question of which pawn to push depends on which pawn Black decides to go after first!} 3...Re1 {It's not clear which line should be considered the main line for Black in the position.} (3...Rh1 4.Ke5! {This time the f-pawn is used} 4...Rxh4 5.f4 Ke3 6.f5 Rxe4+ 7.Kd6= {There is no way for black to round up the f-pawn.}) (3...Kd4 {The last line we will consider here. Other tries make little sense.} 4.h5= {is essentially a repeat of the main line. The other way to draw is to push the f-pawn forward, but this move is the simplest.})  4.h5! {By waiting with the push, White managed to get Black to waste a tempo on stopping the "wrong" pawn, so to speak. Now there is no way for Black to stop the h-pawn in time.} 4...Rh1 5.Kg6 Kxe4 6.h6 Ke5 7.h7=

Ok, so it turns out that White will be able to draw after 1.Rxc2. Although some precise calculation was needed to make sure that White manages to create sufficient counterplay with the pawns, we have to consider far from every possible line.
This is a common theme for practially any endgame: precise calculation is crucial, but the use of certain abstract "guideposts" in the position (such as "Black's king getting to the f-file = White is doomed" in this case) means that we only have to make a relatively small number of precise calculations to reach the correct conclusion. In general, the more endgame theory you know, the more of these abstract "guideposts" will be visible to you, making endgame calculations far more efficient than brute-foring them.


The short story is that the Soviet chess authorities at the time were blocking Korchnoi's progress and severely limiting his opportunities to play, as Karpov had been selected as their favorite son. It was the same sort of impediment that Kasparov later faced when he was on his own path toward dethroning Karpov, and it also echoed the scenario from decades before, when it was rumored/suspected that Paul Keres had been forced to take a backseat to Botvinnik.


In the English Opening, where should the d-pawn go?

Once you play d4 you are usually leaving the pure English opening and transposing to a queen-pawn opening.  Objectively there are positions where it is absolutely better to transpose to a queen-pawn opening but you can certainly build a repertoire around playing the pawn to d3 -- it may just be easier for Black to equalize in some lines.

The formation of c4, d3, e4 with the kings bishop fianchetto'd, knights on e2 and c3 was Botvinnik's baby and is a viable way to play.


Efficient ways to go from pseduo legal to fully legal move generation

This is my understanding:

You have a pseudo-legal move generator
Now, you want to get rid of the illegal moves

How serious do you want your engine be? You can always write a function that takes a position and checks your king. Everytime when you wants to check a pseudo-legal move, you call the function. It will definitely work, and it's simple but it's slow.

Let's study at what a modern engine does. The source code for Stockfish is: https://github.com/official-stockfish/Stockfish/blob/master/src/position.cpp

/// Position::legal() tests whether a pseudo-legal move is legal

bool Position::legal(Move m) const {

Check en passant:

// En passant captures are a tricky special case. Because they are rather
// uncommon, we do it simply by testing whether the king is attacked after
// the move is made.

Do you want move your king?

// If the moving piece is a king, check whether the destination
// square is attacked by the opponent. Castling moves are checked
// for legality during move generation.

You can make the move if it's not pinned. Or it's pinned, but it still protects the king.

// A non-king move is legal if and only if it is not pinned or it
// is moving along the ray towards or away from the king.


Can you solve this queen + 3 pawns vs bishop + 3 pawns chess problem?

If White can get the Black king to the first rank, then it will not be fast enough to catch the g-pawn from promoting.  White starts by playing 1. Qg5, and after 1...Kh7 2. Qf6 Kg8 3. Qh6, the White queen can simply imitate the Black king's movements until she can start forcing the king down towards the first rank.
[FEN "7k/8/8/8/6p1/4QpPb/5PpP/6K1 w - - 0 1"]

 1. Qg5 Kh7 2. Qf6 Kg8 3. Qh6 Kf7 4. Qg5 Kf8 5. Qg6 Ke7 6. Qf5 Ke8 7. Qf6 Kd7 8. Qe5 Kd8 9. Qe6 Kc7 10. Qd5 Kc8 11. Qd6 Kb7 12. Qc5 Kb8 13. Qc6 Ka7 14. Qc8 Kb6 15. Qd7 Ka6 16. Qc7 Kb5 17. Qd6 Ka5 18. Qc6 Kb4 19. Qd5 Ka4 20. Qc5 Kb3 21. Qd4 Ka3 22. Qc4 Kb2 23. Qd3 Ka2 24. Qc3 Kb1 25. Qh8 Kc2 26. Qxh3

As to whether this is the fastest win, I'm not sure.