How many moves needed for a knight to go from any square to any other square? I want to find a sequence of knight moves that has a given origin and destination squares, preferably with the minimum number of moves. I can iterate over knight moves and collect visited squares, until I visit the destination square. I am asking how many iterations would I need to not miss an answer for any given pairs of squares.
I am trying to find the minimum number of iterations needed for looking at piece moves needed to reach from one square to a different square. I know bishops can't reach every square. I guess the knight is the slowest piece, except pawns, thus the title question is right to determine this problem. So I want an answer for every piece to reach every pair of squares.

You are asking for the diameter of the knight's graph. I suppose you only want it for the ordinary 8x8 chessboard. (See OEIS sequence A232007 for diameters of knight's graphs on square boards of size nxn, in particular confirming my answer 6 for the case n = 8. The answer is alleged to be ceiling(2n/3) for n > 4.)
The answer is 6. It takes 6 moves to get from a corner square to the opposite corner, say from a8 to h1.
There are many ways to get from a8 to h1 in 6 moves, e.g. a8-c7-e8-g7-h5-g3-h1.
To see that you can't get from a8 to h1 in less than 6 moves: First note that the Euclidean distance between a8 and h1 (measured from center to center and taking the side of a square as the unit of distance) is sqrt(7^2 + 7^2) = sqrt(98). The length of a single knight move is sqrt(2^2 + 1^2) = sqrt(5), so the maximum distance you can travel in 4 knight moves is 4 * sqrt(5) = sqrt(80) < sqrt(98), so a knight can't get from a8 to h1 in 4 moves or less. But it must take an even number of moves (since a8 and h1 have the same color), so at least 6 moves are needed.
Finally I have to show that you can get from any square to any other in at most 6 moves. This will take a bit of case work.
I. Starting from e4, you can reach any square in at most 3 moves, except the squares a8, c2, c6, g2, g6.
To see this, take an 8x8 grid and write 0 on the square e4. Next, write 1 on each square that can be reached by a knight's move from e4. Next, write 2 on each unmarked square within a knight's move of a square marked 1. Finally, write 3 on each remaining square which is a knight's move from a square marked 2. You will see that every square has been marked except for the five squares a8, c2, c6, g2, g6.
II. Therefore, a knight can get from any square to any other via e4 in at most 6 moves, unless at least one of the two squares is a8, c2, c6, g2, or g6.
III. By the same procedure as in step I, you can show that from c6 you can reach any square in at most 4 moves.
IV. From c2 (or g6) you can reach any square in at most 5 moves.
V. From g2 you can reach any square in at most 5 moves.
VI. From a8 you can reach any square in at most 6 moves.
Therefore, a knight can get from any square of the 8x8 chessboard to any other in a maximum of 6 moves (5 moves if the squares have opposite colors).
P.S. @Laska pointed out in a comment that this argument can be simplified:

I think the sufficiency argument can be simplified as the e4 statement also works for e5, d4 & d5. The tricky squares for e4 are those which are 2xsqrt(2) or 4xsqrt(2) away. No square is this distance from more than one of e4, e5, d4 & d5. So given any two squares there are at least two routes in 6 or less moves. They visit different squares in the centre 4: e4, e5, d4, d5. – Laska


Material value of the Berolina pawn The Berolina pawn is a fairy piece that moves like a normal pawn, but can move two (and one in all other cases) steps diagonally and capture one forward. How much better (or worse) is this piece compared to a normal pawn?

According to Gnu, which has a page dedicated to Berolina chess, the value of the Berolina pawn is the same as in standard chess, = 1. This is unsatisfactory because they give no explanation of how this evaluation was made.
The evaluations for standard chess existed before computer chess programs and were based on hundreds of years of experience playing standard chess. That doesn't exist for Berolina chess which was only invented in 1926 and is little played.
In the absence of similar amounts of over-the-board games of Berolina I think the best approach to getting an accurate evaluation would be an AlphaZero-like simulation of millions of self-learning games which could provide the empirical data upon which a good evaluation could be made.


Joining a league or tournament I've never played in a chess league or tournament before, but I am anxious to try one and find out where my true over-the-board rating stands. I'm too old for the school competitions (over 30) and I'm not sure where to go or what to do to get started.

What would I have to do in order to become involved with the USCF or FIDE, and what steps are involved in actually playing in such a tournament? Is there a standard format or guideline I can read to prepare?

USCF has regular chess tournaments listed in different states each month and you can find tournaments such as Chicago Open, Philadelphia Open, etc, in-which, you can play at any levels (Under 2200, Under 2000, etc). You have to be a USCF member to play these tournaments which is an easy process and you can register and pay it online at the USCF website.

Also tournaments such as Chicago Open,World Open (which is starting today at Philly) are open to all USCF members and you can play at any level. At first, you will be having a provisional rating and if you play at any levels Under 2000 and under, and if you win that level you will not be able to win the full top prize due to your provisional rating. But if you play other higher levels - U2200, U2400 and Open - you will also get a FIDE rating because these levels are usually FIDE-rated. You should always check with the tournament organizers to see which levels are FIDE rated, how much they pay out for unrated players who win and then can play them.

Note: Not all USCF tournaments are FIDE rated. Only Big tournaments such as those mentioned above have FIDE-ratings. (Most of these Big tournaments are organized by CCA - http://chesstournamentservices.com/cca/ )

So playing in a FIDE-rated tournament in USA is as simple as finding the BIG tournament closer to your area and registering for it with a USCF membership. Usually these big tournaments have an entry fee of around USD 300.

These bigger tournaments have different ways to enter the tournament and play - 3 day. 4-day, 5-day etc. It all depends on your other-schedule and you can pick a type of play suitable for you. Some of these big tournaments all allow you to re-enter the same tourney if you lose the first few games and think that you can play well and want to play from the start again. You can always check with the tournament organizers about the rules.

From my experience of playing these big tournaments, playing 3-day tourneys is a hectic schedule where you would play 3 or 4 games in the 1st and 2nd days and then join with the regular round schedule for all day-games. Picking the 3-day tourney instead of 5-day or 7-day is basically based on your free time for that week and how well you can adapt to play all the games to win. It's more of a gamble paying 300 USD (unless playing unrated-level which has very less entry-fee but no prize money) and I don't play these tournaments anymore. I just moved from chess to poker.

If you think you are a good chess-player and want to get a FIDE-rating,  then playing these big tournaments at Under2200 and above would give you a FIDE-rating.


What is the percentage of players who are women in the sections where both men and women can play in? I am NOT asking for the percentage of chess players that are women.

I am asking for the percentage of players who are women in the sections where both men and women can play in.
That percentage is obviously lower than the percentage of chess players that are women because many women prefer to play in women-only sections.

In other words the question could be rephrased as: if I'm a man and tomorrow I'll play a game in a tournament, what's the probability that my opponent is a woman?

You can answer for either USCF or FIDE, it doesn't matter which one.

In France, there are women only team championships but not all women chess players supports them.

Here is the point of view of Mathilde Choisy (WFM, FIDE 2181), in French http://echecsetmixte.fr/?p=665

The main points are :

If you want to make progress, don't think about women competitions, think bigger and aim for results in "general" competitions. A top 20 in French mixed youngster championship is a better result than a top 3 in European Girl championship.
France has only a few active women players rated 2000+ so they always play against each other in these competitions
If you stay too long in girl competitions, you won't realize the gap in level with the boys until it's too late
Women championships promotes "amateur chess" but are no use for professionnal competitions.

It's clearly not an answer to the question but I think it's worth sharing.

Btw I met my wife in an French mixed open, so there are some chances that you'll played against some. I checked the data for this open and here are the rates :

Open A , Elo >1700 : 5-10% women
Open B, Elo <1800 : 12-15% women


Are there any legal positions known to be impossible to come to in a normal game? There are some fairly obvious ways to set up a chess board that cannot possibly happen:  both kings simultaneously in check would be one.

There are some positions that seem impossible in a normal game... for example, one side has all of it's original pawns in their original location and the other side has NONE of its pawns remaining - but with both sides displaying all pieces in their original positions (perhaps knights can do this, I don't know.)

However, seems like there may be some impossible positions that are not at all obviously difficult.

The question is if there are any known legal positions (preferably ones that  a normal human might think are the result of a game) that cannot be played into?

Hi and thanks for the question. The words "legal" and "illegal" are actually defined in the FIDE rules. Basically, a legal position is one which can be reached by a sequence of legal moves.

So, with this definition, I think that you are asking: are there illegal positions which aren't obvious? The answer is "many" Welcome to retrograde analysis! :D

There is already a chess.stackexchange question on this, so I suggest we continue the discussion there: Are there any illegal positions that are difficult to spot?


Why are tablebase files so large? What is the reason that table base files are so large?

I can't think of any other way to phrase that question - but the question alone is rejected by stackoverflow's gateway bot, hence this paragraph added to placate it.

For a simple numerical example, take the endgame of King + Rook + Pawn vs. King + Rook. The number of possible positions is 64 x 63 x 62 x 61 x 60. Of those, 25% is not valid because the pawn is at the first or last row, and because of the symmetry around the d/e file, we only need to store the positions where the pawn is on the a, b, c or d file. This leaves us with 64 x 63 x 62 x 61 x 60 x 0.75 x 0.5 = 343,103,040 positions*.

For every position, you need to know how many moves to mate or conversion, both with White to move and Black to move. You need 2 bytes for each position, so we get a total of 686,206,080 bytes which is about 654 MB. With ZIP-like algorithms, we can compress the size of the files by about 80%, which leaves us with around 150 MB. You can download the files here - note that the tablebases are split between White-to-move and Black-to-move.

For 6- and 7-man endgames, typical sizes are 60 resp. 3600 times as large, so 9 GB resp. 540 GB. Sometimes, symmetry can be exploited further (especially if there are no pawns involved), but this will result in a maximum reduction to 25% of sizes when pawns are involved.

*: actually, some positions are not valid because e.g. both kings attack each other. This number is rather small and if you would filter these, it would take much more time to lookup a certain position in the database.


Wrongly accepted stalemate but game is a clear win? What will happen when we wrongly accepted stalemate and thereafter 02-03 seconds we noticed it was not a stalemate but 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.


Chess apps that provide a 3D view of the board and allow export of PGN I'm looking for an Android chess app that satisfies the following criteria:

Provides a 3D view of the board and the pieces (required)
Allows one to have an account, and invite friends to play matches online (required)
Allows export of PGN (optional)

Could someone suggest such an app?

Chess.com is probably one of the world's most popular online chess platforms. It has an app and a website (which offers many more features, such as a beta 3D view). In both, you can export game PGNs and have an efficient friends system in which you can challenge people to play. There are also many other beneficial features- free lessons from master players, tactics training, vision training and numerous drills to improve endgame play, as well as Stockfish analysis. Hope this answers your question.


Tool for solving puzzles with multiple defense lines, alternative solutions and playing wrong lines until user resigns Looking for a tool for designing chess puzzles with an interface to test the user against all reasonable defenses (not just the single main line), to allow alternative solutions (without the usual bother of try again please), and which continues playing after a wrong move with the help of an engine rather than interrupting the chess experience with "wrong move try again".

The idea is to make the practice of solving problems a real chess experience like an analysis session with a trainer or partner. I am interested in this kind of software whether it is free or not, online or to be installed.

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.


How to mathematically determine if king and pawn versus king endgame is a draw or a win? I am aware of questions such as this one which discussed a method of determining if a king pawn vs king endgame is a draw or not. The accepted answer gave detailed guidelines but is not mathematically strict. I am asking the question again, but from a different angle.

If we label all the squares of the board as 1, 2, ..., 64 and we will use three numbers to denote the position of white king, black king, and white pawn, respectively. Let f be a function whose domain is a subset of {1,...,64}×{1,...,64}×{9,...,56}×{0,1} and whose range is {1/2,1}. Here × denotes the Cartesian product and the third set is {9,...,56} instead of {1,...,64} as it denotes the position of the white pawn. The fourth set {0,1} denotes whose turn it is; 0 for white and 1 for black. For the range, 1/2 means draw and 1 means win for white (assuming both sides only play the best moves possible). The actually domain is a subset of {1,...,64}×{1,...,64}×{9,...,56}×{0,1} instead of the entire set since no two or more pieces can occupy the same square and two kings cannot be adjacent to each other.

With the above definition, f is a function whose domain contains fewer than 64×64×48×2=393216 elements and whose range contains 2 elements. So it is possible (though may be difficult) to express f explicitly.

My question is: How to mathematically determine the output of the function f, given any input and therefore determine if a king and pawn vs king endgame is a draw or not?

In other words, I am looking for a way to find the value of f(x,y,z,w), where x denotes the position of the white king, y for the black king, z for the white pawn, w for whose turn it is and the output of f can only be 1/2 and 1.

You can do this (the space is, after all, finite) but it ends up being tedious, and is probably inferior to just looking it up in a tablebase.

Let's start with one of the most basic concepts in king and pawn endgames: the pawn square. White generally wins if Black is too far away to enter the square. We just need to convert this rule into simpler rules, and then convert those into your mathematical scheme.

If, with White to move, the White pawn is farther advanced than the Black king, White wins. If, with Black to move, the White pawn is 2 ranks farther advanced than the Black king, White wins.
So, if floor(y/8) + w < floor(z/8) then f(x,y,z,w} = 1.

If, with White to move, there are more files between the Black king and the pawn than there are ranks between the White pawn and the 8th rank, White wins. If, with Black to move, there are 2 more files between the Black king and the pawn than there are ranks between the White pawn and the 8th rank, White wins.
So, if abs((y mod 8)-(z mod 8)) + w < (8-floor(z/8)) then f(x,y,z,w} = 1.

But we aren't done yet. If the pawn is on the second rank, it can go an extra square on its first move. But if Black has the move and is next to the pawn, he might be able to capture the pawn right away before it can move those 2 squares.
So, if z is in {9...16}, and w = 0 or (abs(z/8 - y/8 > 1) or abs((z mod 8) - (y mod 8) > 1), then if  ((y mod 8)-(z mod 8)) + w+1 < (8-floor(z/8)) or floor(y/8)+w+1 < floor(z/8) then f(x,y,z,w} = 1.

But we still aren't done. There's an exception to the pawn square rule. Here, Black is outside the square and cannot enter it, but the game is drawn because of stalemate:

[FEN "K7/P7/3k4/8/8/8/8/8 b - - 0 1"]

1... Kc7

So now, to be complete, we'd have to exclude the situation where the White king is in the corner, blocking his own pawn, and Black can trap him in that corner. This function is getting very convoluted already, and that's just one of the most basic concepts.


As Black, how should one respond to 4. Qe2 by White in the Russian Game, Damiano Variation? I recently played a game as Black. My opponent and I transposed into, according to Lichess, the Russian Game, Damiano Variation, when White played 4. Qe2. I wasn’t sure how to reply, and I ended up losing my queen and soon resigned.
[FEN ""]

1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nxe4 4. Qe2 Nf6 5. Nc6+ Be7 6. Nxd8 Kxd8

As Black, how should one respond to 4. Qe2 by White in the Russian Game, Damiano Variation?

Do not play 3...Nxe4 in response to 3. Nxe5.

I feel this important aspect is missing in the other answers. You can see the primary reason it doesn't work in your game - you end up losing the queen. Given that you can't just move the knight after 4. Qe2, your next-best option is to play 4...Qe7 5. Qxe4 d6 (or ...f6), which still results in you losing a pawn. It's not a disaster because Black does have some compensation in the form of superior development, but Black's position is still undoubtedly inferior.

Avoiding this line is the main line of the Petroff, and is much more stable. The main line goes 1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5.d4 d5. Black has gained a tempo (as seen from his advanced knight), but the knight is somewhat exposed and can potentially be forced to retreat, in which case White is up two tempi. In practice, White can usually achieve this, but needs to play pawn breaks like c4, which balances out. The Petroff is thought to be drawish for a reason.


Chess tricks to fool opponents before game There is chess tournament nearing and I am one of the participants. I have been participating in it in the last few years. And once I was fooled by one of my opponents at the start of the game. He acted such as if he was a very bad player and asked me silly questions at the start of the game. And I got fooled and underestimated the opponent. We also played a practice match first and I won it easily (I guess he didn't play that match seriously). And finally in the real match, he won over me. He was not better than me. (Actually, after analyzing the game, I understood that I had done lot silly mistakes in the game probably because I underestimated him).

So finally, I liked that tactic of my opponent and I want to use it. So, I am in search of some things I can say to the opponent before the match due to which he will underestimate me.

Approach you opponent and ask him if he is good. He'll probably respond by saying that he is okay or pretty good. Then tell him how once you played someone who was really good and how you lost in ten moves. Also, it is preferable if you pretend to be 8 years old or younger. As you set up the board, make sure to set the board wrong. Place the knight where the bishop should go, and of course the queen should be misplaced as well. He'll correct you and you will pretend you didn't know. The most important thing is during the game. Make sure you seem undecided. Hover your hand around a random pawn and pretend like your thinking. Then hover around another pawn and do the same. Forget to press the clock a couple times. Do a couple illegal moves. I once had a person do exactly this. He pretend to be a child and oblivious to the rules of chess and I just played really fast and careless and lost. I lost because I didn't take my opponent seriously. Things are not always what they seem, so always keep your eyes open and don't underestimate your opponent. I'm assuming that the tournament you speak of isn't an official uscf because you didn't know how strong your opponents are(rating).


Plan against pawn formation of c4, d5, e4, e3 in the Nimzowitsch defense (or similar positions in the Dunst opening) I'm a 1700-ish player who plays opening systems starting with 1.Nc3 as white and 1. ... Nc6 as black, and generally I'm pretty happy with my results.  But there's one type of setup that I struggle forming a plan against, where my opponent trades bishops on e3 (or e6) recapturing with the f-pawn.  A typical example would be:

[FEN ""]
1.e4 Nc6 2.d4 e5 3.d5 Nce7 4.c4 Ng6 5.Nf3 Nf6 6.Nc3 Bc5 7. Be3 Bxe3 8.fxe3

What should my strategy be as black in this position?  Usually with the dark-squared bishops off the board I would try to place my knight on f4, but that's impossible with the pawn on e3.  I usually end up trying to attack the e3 pawn (with O-O, d6, c6, Ng4, Qb6 in some order), but white has no problem defending that.  Stockfish says the position is even, but I've not scored well in these type of positions and feel kind of at sea.  Any suggestions?

I play systems such as this myself. In your example White has been very unambitious and you are certainly equal at least, but you do not have the advantage that you may feel entitled to. It is worth bearing in mind that nothing is weak unless it can be attacked, and this is true of the doubled pawns here. By focusing on them I believe you are wasting your energy.

I think that the correct attitude for Black is to recognize that you have no weaknesses and an easy development and should be happy with that. Counterintuitively, Blacks strategy should revolve around ..f5, even though this allows White to dissolve his doubled Pawns and perhaps exchange his bad Bishop. This break would be normal if, for example the Pe3 were still on f2, and it is still a good idea. Black can start with ..d6 and ..0-0, then put the Nf6 somewhere and play ..f5. From your diagram play might go 8...d6 9.Bd3 0-0 10.0-0 Ng4 11.Qd2 f5 12.exf Bxf5 13.Bxf5 (13.e4 gives away the square f4 and makes the  White Bishop permanently bad.) Rxf5.  In this position I would prefer (slightly) to be Black.


Must a player play tactical openings to learn tactics? As has been said, Chess in 99% tactics/calculation.

So, if a player is aiming to increase his tactical abilities should he play tactical openings like the King's Gambit, or can he play something like the English if desired, knowing that tactics will show up in the middle game?

Another way to put this is as follows:  should a developing player master the tactical openings before the positional ones, given that tactics are much more important in the short term?

My chess instructor told me:

Tactics
Tactics
Tactics

I think you can win a lot of games at the sub-2000 level with raw tactical skill.  Thereafter, positional considerations start becoming important.

Regarding the opening, I don't think it much matters.  Play the type of opening that makes you happy.


How should a beginner improve gameplay speed? I am a fairly low skill player and am wanting to improve my game, but I feel as though I need to gain at least a bit more speed in my decision making to make better progress. I am a fairly analytical person and because of this I tend to over-analyze a situation and take an extremely long time to deliberate my moves. For example, I have played casual games with friends that ended up taking 2 hours to complete mostly because of my slow-decision making. I really think if I could speed up my gameplay I'd be able to play more games in less time and see more benefit out of that. It would also mean less irritation when playing in person games, which would also be nice.

I would like to clarify that I understand speed isn't normally a main focus for beginners when compared to learning tactics and gaining a more general understanding of the game. However, in my case (and I am sure other people like me) it is a concern. I have considered many options to remedy this issue, such as trying to play with a time-limit, but I fear that may just cause me to rush and make a lot of mistakes. Would I be better off to put in more time to studying tactics and moves so that I just recognize ideal choices faster? I didn't see any questions involving the same problem and any advice here would be helpful.

You should only be spending time on a couple of candidate moves. This might shorten the thinking time if you rapidly dismiss moves that bring nothing to your position.

IM Jeremy Silman says in his book The Amateur's Mind that each move should have at least two purposes (amongst attacking, defending, gaining space, developing, gaining initiative, etc.).

You can also limit the lines you calculate to one and a half move : your move, the opponent's most likely reply, and then your next move.

I hope this helps.


How to tell that this is a draw In an endgame I played as Black, after the rooks were exchanged, the below position was reached. A funky stalemate quickly ensued.

[FEN "8/5ppk/5p1p/8/3K1P2/6P1/7P/8 b - - 0 1"]
[startflipped ""]

1... Kg6 2. Ke4 Kh5 3. h3 g5 4. f5 g4 5. h4

It was a simple endgame to me. as Black, I had an extra pawn and was closer to my pawns then White. I would just exchange pawns and promote my extra. I though that I would win until I stumbled into an unexpected stalemate. Not a big deal, mistakes happen.

But when I put the position into Lichess, surprise, surprise, it was actually a draw! It turns out that White will be able to lock in Black, using Black's doubled pawns against them, and forever keep Black king imprisoned for eternity, thereby drawing the game.

What could I do, without computer analysis, to determine that this and similar endgame positions are a draw? What endgame principles are there/exist that would help?

I had an extra pawn and was closer to my pawns then White

It seems you simply overestimated these two factors.

An extra pawn alone is not a decisive advantage, it matters a lot where it is located. If the f7 pawn was on a7, you'd win.

The kings are actually positioned to your disadvantage, White's is nicely centralized and yours is stuck in the corner. If the White king was on g2 and yours on e4, you'd win.

But most of all, chess endgames are concrete. If you shift the whole position one file to the left, the engine does indeed see black winning!

What makes your position a draw is the unfortunate pawn formation: Your own doubled pawns trap your own king in the corner, while White's are flexible enough to shut the position from the front. And as said, his king is well positioned, it can either block the escape of yours via d8 or assist his own pawns in preventing the frontal breakthrough.


When will the 2018 FIDE Candidates tournament be held, and who will qualify for it? We've just had the World Championship match between Carlsen and Karjakin, so one qualifier for the next Candidates is known: Karjakin.

I assume it will be held in 2018, is anything more known about the date?

What are the rules for qualification of the other players?

The Candidates will be held in Berlin, Germany, on 10-28 March 2018 (source).

According to FIDE's Rules & Regulations for the Candidates Tournament of the FIDE World Championship cycle 2016-2018, the following will qualify, in order of priority:

1. The loser of the previous World Championship Match -- Sergey Karjakin.

2. The 2 finalists of the FIDE World Cup 2017 - Ding Liren and Levon Aronian.

This is a 128-player knockout tournament, currently being held from 1 to 25 September 2017, in Batumi, Georgia, with the final in Tbilisi, Georgia (see Wikipedia, which also has details about qualifiers to the World Cup that go too far for this answer).

Karjakin and Carlsen played the World Cup so a situation could have arisen where a player not in the final would qualify, but they were both eliminated.

Quarter finals:

Maxime Vachier-Lagrave beat Peter Svidler 2.5 - 1.5
Wesley So beat Vladimir Fedoseev 1.5 - 0.5
Ding Liren beat Richard Rapport 1.5 - 0.5
Levon Aronian beat Vassily Ivanchuk 1.5 - 0.5

Semi-finals:

Levon Aronian beat Maxime Vachier-Lagrave 5-4
Ding Liren beat Wesley So 3.5 - 2.5

Final (not relevant for the Candidates, but for completeness):

Levon Aronian beat Ding Liren 4-2

3. The top 2 winners of the FIDE Grand Prix 2016/2017.

There are four events:

18-27 February 2017, in Sharjah, United Arab Emirates
12-21 May 2017, Moscow, Russia
6-15 July 2017, Geneva, Switzerland
16-25 November 2017, Palma Majorca, Spain

Top standings after 3 events:

Shakhriyar Mamedyarov (3/3 events played): 340
Alexander Grischuk (3/3): 336 3/7
Teimour Radjabov (2/3): 241 3/7
Maxime Vachier-Lagrave (2/3): 211 3/7

(players with 3 events and insufficient points left out)

4. The 2 players not otherwise qualified with the highest average rating (among those that participated in the WC or GP).

Calculated using the 12 rating lists from january 1 to december 1, 2017.

| Name                      | Avg  | Jan  | Feb  | Mar  | Apr | May | June| July| Aug | Sep | Oct | Nov |
|---------------------------|------|------|------|------|-----|-----|-----|-----|-----|-----|-----|-----|
| Caruana, Fabiano          | 2808 | 2827 | 2827 | 2817 | 2817| 2802| 2808| 2807| 2807| 2799| 2794| 2799|
| So, Wesley                | 2806 | 2808 | 2822 | 2822 | 2822| 2815| 2812| 2810| 2810| 2792| 2788| 2788|
|---------------------------|------|------|------|------|-----|-----|-----|-----|-----|-----|-----|-----|
| Vachier-Lagrave, Maxime   | 2796 | 2796 | 2796 | 2803 | 2803| 2795| 2796| 2791| 2789| 2804| 2794| 2796|
| Mamedyarov, Shakhriyar    | 2786 | 2766 | 2766 | 2772 | 2772| 2772| 2800| 2800| 2797| 2797| 2791| 2802|
| Nakamura, Hikaru          | 2785 | 2785 | 2785 | 2793 | 2793| 2798| 2785| 2792| 2792| 2781| 2774| 2780|
| Anand, Viswanathan        | 2785 | 2786 | 2786 | 2786 | 2786| 2786| 2786| 2783| 2783| 2794| 2783| 2783|

5. One organiser's nominee.

Vladimir Kramnik was chosen as the wildcard.

This could have been player with a rating of 2725 or higher in one of the rating lists in 2017.

Next update: the final Grand Prix, result 25 november.


Looking for openings by pawn structure Sometimes when playing Alekhine defense Scandinavian Variation, I get this kind of pawn structure :

8/p6p/6p1/2p1p3/2PpP1P1/Pp1P4/1P6/8 w - - 1 29

I am very comfortable playing as black with this structure, but there is it not the most common structure I would get in Alekhine, so are there any openings which may result in this (or similar structure) ?

I'm assuming you're mainly referring to the central pawn mass - wanting to get a structure with a Black pawn on b3 seems too specific.

In general, it's much harder to deliberately maneuver the game into a line where you are the person with the pawn on d4 (or if you're playing White, with the pawn on d5). This is because you need to get your opponent to provoke your d-pawn forward with e4 and c4. If you liked playing the White side of that diagram, I would recommend playing the Czech Benoni as Black (i.e: 1.d4 Nf6 2.c4 c5 3.d5 e5 4.Nc3 d6).

If you want a higher chance of getting the structure with c4-, d5-, and e4-pawns (so basically being on the flipped side of Black in that diagram), I'd recommend playing 1.d4 and 2.c4 as White. Your opponent could go into the aforementioned Czech Benoni (although it isn't very common), or they could play the King's Indian Defense. In that structure, Black often plays ...e5/...c5, and once in a while pushes both pawns (getting you into a situation you want).

I don't have much advice for how to get that structure as Black. You're at the mercy of your opponent to dictate the play. One of the most common ways I know of getting it is if White plays a reverse King's Indian, allowing you to push all your pawns with ...d5, ...c5, ...e5, but most people don't do this.


When are both the rank and file required for disambiguation of a move in PGN/SAN? The PGN "Standard" (if you want to call it that, because it is very flawed and seems out of date), states:

First, if the moving pieces can be distinguished by their originating files, the originating file letter of the moving piece is
inserted immediately after the moving piece letter.
Second (when the first step fails), if the moving pieces can be distinguished by their originating ranks, the originating rank digit
of the moving piece is inserted immediately after the moving piece
letter.
Third (when both the first and the second steps fail), the two character square coordinate of the originating square of the moving
piece is inserted immediately after the moving piece letter.

What I want to know is this: what situation could give rise to the third case?
As I think this through, I cannot for the life of me think up a scenario that the first or second disambiguation rules wouldn't comprehensively cover.

Yes, it's possible for a piece to need both the rank and file to distinguish it, although it's rare. For example:
[FEN "8/1k6/8/8/5Q2/8/3Q1QK1/8 w - - 0 1"]

1.Qf2e3


The Sicilian Defense Kalashnikov Variation: Why shouldn’t white play 5.Nxc6 here? I get a lot of weaker players, who opt out of main lines, and they play 5.Nxc6?! against me. It has seemed to happen a lot lately. Why is that bad, and why shouldn’t white play that?

Note: This is more of a teaching question as I intend to answer my own question.

 [FEN ""]

 1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 e5 5. Nxc6?!

First, it is important to know that in many Sicilian positions, not just the Kalashnikov, if black gets in d5, he has equalized, and has a very free game. Thus, taking on c6 helps black reinforce the center, and he will often get in d5 soon. White following up the trade with Bc4, which scores only 20% for white despite white out-rating black 2376 to 2192 per Mega 2020, makes it that much more impactful if black does get in d5 since white will be forced to lose yet another tempo.

In addition, black will soon play Rb8 with a lot of pressure against b2, or if white plays b3, there will be chronic weaknesses on the queenside dark squares, and that could lead to Bb4xc3, and e4 may hang under certain circumstances. Black will also eventually get long-term pressure down both the b- and c-files, combines with a5-a4, should white exchange after an eventual d5 by black. These pawns may look strong, and they would be in the endgame, but in the middlegame, they are just huge targets on open files.

Also, of note is that in most situations, if white plays the natural Bg5, either simply h6 wins the bishop pair, or Qa5 can get out of the pin tactically.

 [FEN ""]

 1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 e5 5. Nxc6 bxc6 6. Bc4 (6. Nc3 Nf6 7. Bg5 $6 Rb8 8. Rb1 h6 9. Bxf6 (9. Bh4 $4 Qa5 10. Bxf6 Rxb2 $1 11. Kd2 Bb4 12. Rxb2 Bxc3+ 13. Kc1 Qa3 $19) (9. Bd2 d5 $17) 9... Qxf6 10. Bc4 Bc5 11. O-O O-O 12. Qe2 Bd4 13. Na4 d5 14. exd5 Bf5 15. dxc6 Qxc6 16. Nc3 Rfc8 {With huge pressure for the pawn.}) 6... Nf6 7. Nc3 Bb4 (7... Bc5 $5 {Is also possible, with the idea Bd4.}) 8. O-O O-O 9. Bg5 h6 10. Bh4 g5 11. Bg3 Qe7 12. Qd3 Rd8 13. Rfe1 d6 {And although white is holding it together, it is still not pleasant. The Bg3 is not doing much, the Qd3 is not comfortable being opposed by the Rd8, and black will continue trying to create weaknesses on the queenside with Rb8.}


Have famous grandmasters ever been checkmated? Whenever I watch chess games played by grandmasters, they usually resign far before reaching checkmate (often even before a forced checkmate occurs). However, I wonder if there are recent examples of famous grandmasters getting checkmated?

Would be interesting to see how the game looks in order for them to get checkmated. Is there any examples of this?

The most recent super Grandmaster level checkmate I can think of is the game Wesley So vs Hikaru Nakamura, Sinquefield, Cup August 2015.

[White "Wesley So"]
[Black "Hikaru Nakamura"]
[Result "0-1"]
[FEN ""]

1. d4 Nf6 2. c4 g6 3. Nc3 Bg7 4. e4 d6 5. Nf3 O-O 6. Be2 e5 7. O-O Nc6 8. d5
Ne7 9. Ne1 Nd7 10. f3 f5 11. Be3 f4 12. Bf2 g5 13. Nd3 Ng6 14. c5 Nf6 15. Rc1
Rf7 16. Kh1 h5 17. cxd6 cxd6 18. Nb5 a6 19. Na3 b5 20. Rc6 g4 21. Qc2 Qf8 22.
Rc1 Bd7 23. Rc7 Bh6 24. Be1 h4 25. fxg4 f3 26. gxf3 Nxe4 27. Rd1 Rxf3 28.
Rxd7 Rf1+ 29. Kg2 Be3 30. Bg3 hxg3 31. Rxf1 Nh4+ 32. Kh3 Qh6 33. g5 Nxg5+ 34.
Kg4 Nhf3 35. Nf2 Qh4+ 36. Kf5 Rf8+ 37. Kg6 Rf6+ 38. Kxf6 Ne4+ 39. Kg6 Qg5#


How come this king and knight + rook pawn vs king endgame not drawn? Here is a picture of the starting position. White to move.

[FEN "8/8/8/3nk1pp/8/3K2PP/5P2/8 w - - 0 1"]

1. f3 h4 2. f4+ gxf4 3.gxf4+ Kxf4 4. Ke2 Kg3 5. Kf1 Kxh3 6. Kg1 Kg3

1. f3 h4

2. f4+ gxf4 (to make it into king and knight + rook pawn endgame which is drawn)

3.gxf4+ Kxf4

4. Ke2 (to reach the g1 and h1 squares to draw)

4... Kg3

5. Kf1 Kxh3

6. Kg1 Kg3

I forgot the rest of the moves, but somehow it's losing for white. I thought a king and knight + rook pawn is always drawn if the opponent's king can reach the g1 h1 squares. Why didn't it work this time and when are these endgames drawn?

You're confusing this theoretical endgame with K+B+P vs K.

If the bishop doesn't match the promotion square of a or h file that the pawn is on, then the pawn can not promote in your scenario.

On the other hand, the knight can go to any square on the board potentially so the h1 square can be covered by it.

I suggest going to the link below to understand how to force the king out of the corner. Ideally you should get this position with white to play, and check to force Kg8 and push the pawn.

http://www.chesskit.com/training/endgame/KNPk/1/index.php


Is ECO still the best reference for all chess openings? Is ECO, Encyclopedia of Chess Openings still considered the best printed reference work for all the chess openings, as it was back in the '80s?

There does not seem to be a consensus on this, but here is a relevant discussion:

https://www.chess.com/forum/view/chess-equipment/chess-opening-reference-books?page=1

For printed opening material (as you requested) I prefer ECO with Chess Informant updates for new opening ideas and analysis:
http://www.chessinformant.org/about-chess-informant/


What is the best move in this puzzle rush? [FEN "2b2r1r/2k1q1b1/2p1p2p/1p1pPp2/pP1P1RB1/P1N5/2P1Q1PP/5RK1 w - f6 0 1"]
[starpPly "2"]

1. Bh5?

In this puzzle rush from chess.com, it says that Bh5 is the wrong move, although Stockfish shows it as the best. So what is the best possible move? It's the  17th puzzle and it is rated at 1124 ELO.

Did black just play f5 before? Then the right move is exf6 en passant, Bxf6 Rxf6 Rxf6 Qe5+ and win the piece.
[FEN "2b2r1r/2k1qpb1/2p1p2p/1p1pP3/pP1P1RB1/P1N5/2P1Q1PP/5RK1 b - - 1 1"]
[StartFlipped "0"]
[StartPly "3"]

1... f5 2. exf6 Bxf6 3. Rxf6 Rxf6 4. Qe5+


Why are games more likely to last 60, 80 and 120 moves? I've downloaded and parsed the king-base chess database (about 1.5 million games) and am looking at distribution of moves for games. When plotting the distribution for different outcomes, I see spikes at 80, 100 and 120 moves (and smaller spikes for draws at 20, 40 and 60 moves).

Why are these spikes occurring? Are people more likely to resign at these round numbers? Or are there rules in professional games that mean games are more likely to end after multiples of 20 moves?

This is due to time control:

  the World Chess Federation FIDE sets a single classical time control for all major FIDE events, according to the handbook: 90 minutes for the first 40 moves, followed by 30 minutes for the rest of the game, with an addition of 30 seconds per move

Other time controls are used, but are usually based on multiples of 20 moves.

Mikhail Botvinnik, a former world champion, once said:

  The amount of errors made at time control are legion

So gross errors accumulate around the 20th, 40th, 60th etc. move, and so would resignations, loss on time and draw offers.


What does 6 and 2 going mean? I am watching an annotated chess game, and the narration goes like this:

  The game I am about to show you was played in the last round of an open tournament in Bad Weise, Germany. My score was 6 and 2 going.

What does the last sentence mean?

"6 and 2 going" is not idiomatic English or chess-speak.

My first assumption is that there are words missing and the speaker actually said or meant "My score was 6 and 2 going into this round." This means that s/he earned 6 points out of the possible 8 in the previous 8 rounds (you get 1 point for a win, 1/2 point for a draw, and 0 points for a loss) before the game being annotated.


Has there ever been a grandmaster-level win where a queen did not move nor get taken throughout the game? Has there ever been a grandmaster-level win where the queen of the side that won did not move nor get taken throughout the game?

I feel like this is possible even at such a level as the side whose queen does not move could still castle but would need to position their rooks, knights and bishops very tactfully.

As noted in the first comment to your question, there are certainly a lot of draws. To narrow it down to reasonable games that were wins, I searched the Mega 2019 Database for games with both players above 2500, and wins with moves between 4-10. It returned 131 games. Of those games, whether due to the remaining moves simply not being transmitted, someone losing for some reason like time or forfeit, or just the wrong result being reported, most were still bogus and equal at the end.

I went through the games quickly looking at the final position looking for games that were truly lost. I also left out a few Internet games that were clear premove/mouseslips like a GM hanging his Qd8 on move 6 to a Bg5. One game might have been legitimate, but a touch-move error with an ill-timed Rg1, so I also left that game out. I found these games that made sense. One has a very instructive tactic!

Let's start off with the least interesting example with a rare case of GM blindness, and simply blundering a piece.

 [FEN ""]
 [Event "Bad Homburg"]
 [Site "Bad Homburg"]
 [Date "1997.07.31"]
 [Round "6"]
 [White "Lutz, Christopher"]
 [Black "Dautov, Rustem"]
 [Result "0-1"]
 [ECO "B12"]
 [WhiteElo "2590"]
 [BlackElo "2595"]

 1. e4 c6 2. d4 d5 3. e5 c5 4. dxc5 e6 5. Be3 Nh6 6. Nf3 Nc6 7. c3 Nf5 8. Bf4 Bxc5 9. Bd3 Nh4 10. Nbd2 Nxg2+ 0-1

The second game has a very cool tactic that I have seen a few times. White calculated cxd7+ expecting Qxd7 and then capturing on e2, but forgot about Nxd7 leaving the Bg5 hanging.

 [FEN ""]
 [Event "Kolkata op 3rd"]
 [Site "Kolkata"]
 [Date "2018.05.21"]
 [Round "8"]
 [White "Sengupta, Deep"]
 [Black "Narayanan, Srinath"]
 [Result "0-1"]
 [ECO "D00"]
 [WhiteElo "2563"]
 [BlackElo "2525"]

 1. d4 Nf6 2. Bg5 d5 3. e3 c6 4. Bd3 Bg4 5. Ne2 Nbd7 6. f3 Bh5 7. O-O Bg6 8. c4 e6 9. cxd5 Bxd3 10. dxc6? Bxe2 (10...Bxe2 11.  cxd7+ Nxd7!) 0-1

And the last game is between the most famous players, although it is a rapid game.

 [FEN ""]
 [Event "EU-ch Rapid-30'"]
 [Site "Cap d'Agde"]
 [Date "1996.??.??"]
 [Round "?"]
 [White "Leko, Peter"]
 [Black "Ehlvest, Jaan"]
 [Result "1-0"]
 [ECO "B07"]
 [WhiteElo "2630"]
 [BlackElo "2660"]

 1. e4 g6 2. d4 Bg7 3. Nf3 d6 4. c3 Nf6 5. Bd3 O-O 6. O-O c5 7. h3 Nc6 8. d5 Na5 9. Re1 e5 10. b4 1-0


Endgames with long king marches I am doing a study that focuses on endgames which involve well-timed king marches, namely endgames in which the winning idea lies mainly in king positioning rather than the coordination of minor pieces for example (although this is a key idea in almost every endgame). As soon as I started stumbling upon this very specific type of endgames, I remembered a famous game from Magnus Carlsen, in which he marches with the king for a consecutive series of move (about 5-7 moves), diagonally to the other side of the board, establishing a key position for his king as soon as possible and winning the endgame. Unfortunately I cannot recall which game it was, nor the time/opposition, if I'm not mistaken there were no rooks left on the board.

I admit this is very little information given to find the game, but that's all I could remember for now. Although he tends to play a lot of endgames because of his style, I do recall that game getting famous because of its fearless long king march. Here I am asking about it, in the hope that someone else may remember this game, or provide any additional information about it.
In any case, if you know of similar endgame plays, please do feel free to post about them here, as a comment or answer, as they are relevant to the study at hand anyway.

Here are a couple of games I found (although they do not really feature a diagonal king march):

Carlsen - Hracek
Carlsen - Pelletier
Adly - Carlsen
Carlsen - Aronian
Kramnik - Carlsen
Pelletier - Carlsen

I cannot resist adding following king marches:

Short - Timman, the most elegant king march I have ever seen.
Gashimov - Grischuk, the most chaotic king march I have ever seen.
Navara - Wojtaszek, the bravest king march I have ever seen. It should be added that it was part of Navara's preparation.


Guarding my seventh rank and a king walk assualt A few weeks ago. I won a game as Black on lichess.com..
[FEN ""]
[startply "48"]

1. e4 c5 2. Nf3 d5 3. Bd3 c4 4. Be2 e6 5. d4 cxd3 6. Qxd3 Nc6 7. exd5 Qxd5 8. a3 Nf6 9. c4 Qxd3 10. Bxd3 Bc5 11. O-O O-O 12. Be3 Bxe3 13. fxe3 e5 14. Ng5 h6 15. Ne4 Nxe4 16. Bxe4 Be6 17. b3 Rac8 18. Nc3 b6 19. Rad1 Ne7 20. Bd5 Bxd5 21. Nxd5 Nxd5 22. Rxd5 f6 23. Rd7 Rf7 24. Rfd1 Rc7 25. Rd8+ Kh7 26. h4 Kg6 27. g4 h5 28.  gxh5+ Kxh5 29. Rh8+ Kg4 30. Kg2 Kf5 31. Rf1+ Ke4 32. Rf3 Kd3 33. Rd8+ Rcd7 34. e4+ Kxe4 35. Rh8 Kd4 36. Kg3 e4 37. Rf4 Rde7 38. h5 Kd3 39. Rf1 e3 40. Rd1+ Kc2 41. Rh1 e2 42. Re1 Kd2 43. Kf2 f5 44. Rd8+ Kc3 45. Rxe2 Rxe2+ 46. Kxe2 Kxb3 47.  Rd3+ Kxc4 48. Kd2 f4 49. Ke2 f3+ 50. Kd2 f2 51. Rc3+ Kb5 52. Rb3+ Ka4 53. Kc3  f1=Q 54. Rb4+ Ka5

To solidify my position, I pushed my pawns forward to create chains on both sides of the board. In order to defend against a rook infiltration, I doubled my rooks on my own seventh rank in order to guard my pawn. I then went on a long King walk and won a few pawns. Finally, I pushed my new passed pawns and promoted for the win.
However, in hindsight, I'm not so sure it was a good strategy. My opponent defended inadequately, so I can't tell. How sound was my long-term strategy?

White was slightly better after 23.Rd7. This is one of those cases where you should have gone for activity with 23...Rcd8! Now, if he just doubles with 24., you can trade and then play Rf7; or if 24.Ra7 then Rd3 with active counterplay and better chances, but white is still better.

That said, the reason you won is that white knows nothing about the endgame, and tried to mate you with h4 and g4, and that is not what the position called for. He only weakened his position, and improved your K since there was not going to be any mate on g4 or e4. It required a gradual improvement of the white K, and then the gradual advancement of the q-side pawns.

By the time you started advancing e5-d4, that was generally the right plan, but you should have started with 36...f5 first so the pair could not be blockaded with Rf4.

In any case, you were already cruising by then.


How did chess change over the 2010s and should I keep anything in mind for buying books from before 2010? I presume I am being overly paranoid regarding this, and I definitely don't intend to turn away from older books at all, but were there any developments opening-wise, middlegame-wise, or endgame-wise during the decade that books from before would overlook or fail to cover?

Given that you are even asking this question, I am going to be a bit presumptuous and guess you are, like me, not a highly rated (elo > 2000) player.
For chess books that are not about opening theory, I would not worry too much about the age of the book. Sure, the occasional study or evaluation has been adjusted based on computer engines, but these are surprisingly rare and inconsequential for most of us. Endgame theory has changed little in the last 50 years and that which has is mostly relevant only to very highly rated players. If Bobby Fischer were to teleport from 1972 to today, he would still be a very good chess player and he learned from books which are considered ancient today.
Opening theory does change more frequently but even then, this is mostly of concern to highly rated players looking to extract tiny advantages from deeply memorized computer lines. If your intention is to simply get a feel for a specific opening and its common variations, I think anything reputable from the last 20 years will be helpful, although you should probably complement this by looking at up to date chess databases to make sure popular variations are covered. Which you should do anyway even with a new book.


Why do FIDE tournaments have rest days on weekends? I'm one of those sad geeks that, instead of watching football of some sort or another, prefer to watch the super GM's battle it out whenever my schedule allows. This weekend I was looking forward to following the FIDE Grand Prix Series, just to find out to my dismay that they are having a rest day on Saturday.

Now I understand that chess is a demanding game and that GM's need their rest, but why do they schedule rest days over the weekend, when spectator interest is at its highest?

Why not have rest days on Mondays and Thursdays, for example? Or alternatively, have a system where players have various rest days, but there is at least one game going on every day for the duration of the tournament.

Surely it is in the interest of the game to maximise the spectator value, which in turn improves the commercial value of the game?

I would say the problem is that the Grand Prix is a Fide organised tournament. If you see how often those tournaments are played in almost completely empty halls, it is obvious that Fide doesn't much care about spectator value.

Some other tournaments conveniently have an uneven number of players, which leads to an extra rest day for each player, "unnoticeable" to the spectator.

Generally non-Fide tournaments try to maximise the income from visitors, which means the weekends have to be played (From the top level tournaments I visited, I would estimate that weekend days draw double to triple the number of visitors compared to workdays.).


Help trying to invent a tactical chess opening I need help!

I am trying to invent something out of my own imagination. But something isn't right... I am playing as white and I can't figure out why is it that I have the feeling about losing a pawn on c3?

[FEN ""]

1. Nf3 Nf6
2. g3 g6
3. Bg2 Bg7
4. O-O O-O
5. c3 Nc6
6. b3 d5
7. d4 Bf5
8. Be3 Ne4
9. Nh4 Qd7

Any suggestions and opinions will be much appreciated.

The Be3 would make more sense on b2 since that would not only support c3 and d4, but also make room for opening the centre via e4 later (after Rf1-e1). Placing a bishop on the 3rd rank in the centre with the pawn behind still on the 2nd rank tends to become awkward.


What are strategic elements for a correct piece sacrifice? I want know which plus elements need to have in general positions for a correct piece sacrifice! Or how do you know that a sacrifice is correct in complicated position?

There is no general rule for a correct sacrifice, however sacrifices are made with different ideas and strategies, such as, to get a huge space advantage, to initiate attack, to cause trouble to the king by opening up it's surrounding pawns, etc. But at the end you have to make sure that your compensation for the sacrifice is pretty good before you actually give up material, and that can only be done by precise thinking in the game. Some of the things you have to keep in mind before sacrificing your material are;

You have good compensation for your sacrifice; i.e. you are gaining something back such as attack, space, gain back opponents material of same value or higher, or mate at some point.
You are defending loss of higher material, avoiding opponent's dangerous attack, defending mate.
Making sure of not going into a neutral position or causing no trouble to your opponent after giving up a sacrifice. This would just make you have less material for nothing.

Here are few examples of famous sacrifices, going through these kind of games will help you understand patterns of sacrifices and ideas behind it. (Make sure to read comments which will appear in the lower box of the game for most moves
) :

The strategical Exchange Sacrifice in Sicilian:

In the Sicilian Defense the exchange sacrifice on c3 is quite typical. In Dragon lines it is almost mandatory to sacrifice a rook for the knight on c3.

What advantages does black usually get? First of all, black gets a ruined pawn structure for white. Secondly, Nc3 was a defender of the central squares d5 and e4, and by eliminating it black can take over the center. Lastly and most importantly, black can launch a dangerous attack on the weak squares around white’s king, since Nc3 was the main defender of the queenside. All of these are major advantages that black gets in return for a material loss. The disadvantage of such an exchange is that if white successfully defends, white might just win because he is up on material. There is also a curious phenomena in such positions: sometimes endgames down an exchange favor black. This is because black’s pawn structure is compact and he usually has no weaknesses. There are no open files for white’s rooks to penetrate, making them not that active.

The following first example shows the attack that black gets for the sacrifice, while the next example shows the endgame.

[Event "WchT 4th"]
[Site "Luzern"]
[Date "1997.10.27"]
[Round "3"]
[White "Arencibia Rodriguez, Walter"]
[Black "Ivanchuk, Vassily"]
[Result "0-1"]
[ECO "B95"]
[WhiteElo "2550"]
[BlackElo "2725"]
[Annotator "Tyomkin,D"]
[Setup "1"]
[FEN "2rqk2r/1b1nbppp/p2ppn2/1p4B1/3NPP2/P1NB3Q/1PP3PP/2KR3R b k - 0 12"]
[Plycount "19"]
[Eventdate "1997.10.??"]
[Eventtype "team"]
[Eventrounds "9"]
[Eventcountry "SUI"]
[Source "ChessBase"]
[Sourcedate "1998.01.31"]

1...Rxc3 { Black destroys the main defender of white's king and sets
the targets of c3 and a3 for attack. } 2.bxc3 Nc5 { Black decides to bring his
knight to attack instead of taking on e4, even though taking on e4 gave black a
slight edge. } ( 2...Nxe4 3.Bxe7 Qxe7 4.Bxe4 Bxe4 ) 3.Bxf6 ( 3.e5 dxe5 4.fxe5 Nfe4 5.Bxe7 Qxe7 { leaving white with a weakened pawn
structure (a3,c3,e5) } ) ( 3.Rhe1 Qa5 4.Qf3 Qxa3+ 5.Kd2 b4 ) 3...Bxf6 4.Rhe1?? { Now black proceeds with his attack. White had to
be very creative to find the right defense. } ( 4.e5! dxe5 5.Nxb5! { the
point of e5, now Qd8 feels very uncomfortable under X-Ray from Rd1 } 5...Ke7! 6.fxe5 Bg5+ 7.Kb1 axb5 ( 7...Qb6? 8.Qg3 Bh6 9.Qh4+ ) 8.Qg4 Kf8 9.Bxb5 Qe7 { Tyomkin,D } ) 4...Qa5 { There is no way white can
hold this position together. } 5.e5 dxe5 6.fxe5 Bg5+ 7.Kb1 ( 7.Kb2 Na4+ ) 7...Bd5 { Black has a wide selection of ways to win. } ( 7...Qxa3 { Ftacnik } 8.Bxb5+! ( 8.Nxb5 axb5 9.Bxb5+ Kf8 10.Qg4 ) 8...axb5 9.Nxb5 Qa5 10.Nd6+ Ke7 ) 8.Nb3 ( 8.Qh5 { Ftacnik } 8...Qxa3 9.Qxg5 Na4 10.Bxb5+ axb5 ) 8...Qxa3 9.Bxb5+ axb5 10.Rxd5 Na4! ( 10...Nxb3 11.cxb3 Qxb3+ 12.Ka1 O-O )
0-1

    [Event "Sochi FIDE GP"]
[Site "Sochi"]
[Date "2008.08.14"]
[Round "13"]
[White "Karjakin, Sergey"]
[Black "Radjabov, Teimour"]
[Result "0-1"]
[ECO "B78"]
[WhiteElo "2727"]
[BlackElo "2744"]
[Annotator ",User"]
[Setup "1"]
[FEN "2r2k2/1p2pp2/p2p1bp1/q3n2n/3NP1b1/1BN1Q3/PPP5/1K4RR b - - 0 20"]
[Plycount "65"]
[Eventdate "2008.07.31"]
[Eventtype "tourn"]
[Eventrounds "13"]
[Eventcountry "RUS"]
[Eventcategory "19"]
[Source "ChessBase"]
[Sourcedate "2008.10.01"]

1...Rxc3!? 2.Qxc3 ( 2.bxc3 { staying in the middlegame might have been a
better option for white } 2...Qc5 3.Rh2 a5 4.Rhg2 Bd7 ) 2...Qxc3 3.bxc3 { at
this stage black would try to improve his pieces, bring his king up and start
pushing his pawn majority on the kingside to create a passed pawn there } 3...e6 4.Bc4 ( 4.Rh2 Ke7 5.Rhg2 Bh3 6.Rd2 g5 { doesn't give much to white } ) 4...Nxc4 5.Rxg4 { this trade does not improve white's position because now
black gets the c4 square for his knight } 5...Be5 6.Rg2 b5 7.Rf2 Kg8 8.a4 ( 8.Rhf1 Ng3 9.Re1 b4! ) 8...bxa4 9.Ka2 Nf6 10.Re2 d5 11.exd5 Nxd5 { now black
has perfectly placed pieces and three passed pawns on the kingside. While
before it was not clear who is better, now it is obvious that black is better,
since white has no counterplay. } 12.Rh3 Bxd4 13.cxd4 Nf4 { winning back one
of the exchanges } 14.Reh2 Nxh3 15.Rxh3 g5 16.Rg3 f6 17.Rc3 Nd2 18.Rd3 Ne4 { now the passed pawns decide the game } 19.c4 Kf7 20.c5 g4 21.c6 Ke7 22.d5 exd5 23.c7 Kd7 24.Rxd5+ Kxc7 25.Rf5 g3 26.Rf4 Kd7 27.Kb2 Ke6 28.Rxe4+ Kf5 29.Re1 Kg4 30.Kc2 g2 31.Kd2 Kg3 32.Ke2 a3 33.Ra1 a2
0-1

EXAMPLES OF TACTICAL SACRIFICES

1- This game was played between Lasker, Emanuel vs. Bauer, Johann Hermann in 1889.
White sacrifices his double bishop to get a whooping attack on Kingside, and also sacrifices rook later in the game but to regain it and also win the game.

[Event "International Tournament"]
[Site "Amsterdam"]
[Date "1889.08.26"]
[Round "1"]
[White "Lasker, Emanuel"]
[Black "Bauer, Johann Hermann"]
[FEN "r4rk1/1b2bppp/ppq1pn2/2ppB3/5P2/1P1BP1N1/P1PPQ1PP/R4RK1 w - - 0 14"]

1.Nh5! { White threatens to
eliminate the king's only defender, and Black can do little to stop him. Bauer,
however, was still unperturbed: he figured that 1...Nxh5 followed by 15...f5
would nip White's shenanigans once and for all. } 1...Nxh5?! { Bauer must have
already written 15.Qxh5 on his score sheet, and contentedly leaned back in his
chair. As you probably already know, Lasker had very different plans. } ( 1...Rfc8 { This move would have been a real spoiler, as White must content himself
with an extra pawn and long-lasting attack after } 2.Nxf6+ Bxf6 3.Bxh7+! Kf8 ( 3...Kxh7 4.Qh5+ Kg8 5.Bxf6 gxf6 6.Qh6! d4 7.Rf3 ) 4.Qg4 { Of
course, Lasker would have had no trouble winning this position as well, but at
least Black could have avoided the double-bishop sacrifice. } ) 2.Bxh7+!! { A
devastating intermezzo. White gives up the pride of his position in order to
damage Black's kingside pawn shell and  -  more importantly  -  mobilize his
queen with check. } ( 2.Qxh5? f5! ) 2...Kxh7 3.Qxh5+ Kg8 { But what now?
The tempting 4.Rf3 is dreadfully slow, and after 4...f6 Black's king will
have a permanent escape route. Of course, Lasker has everything under perfect
control. } 4.Bxg7! { Snap! Crackle! Pop! Amazingly, White gives up another
bishop to destroy the pawn shell. Black has no choice but to recapture, but
his king is sent from the frying pan right into the fire. } 4...Kxg7 ( 4...f6 5.Bh6 Qe8 6.Qg4+ Kh7 7.Qg7# ) 5.Qg4+ { It is crucial to drive the king to
the h-file before mobilizing the rook. The immediate } ( 5.Rf3?? { let Black
off the hook: } 5...Rh8 6.Rg3+ { and now the amazing } 6...Bg5! 7.Qxg5+ ( 7.Rxg5+ Kf6 8.Qg4 d4! ) 7...Kf8 { turns the tables. } ) 5...Kh7 ( 5...Kf6 6.Qg5# ) 6.Rf3 { White threatens Rh3, and it appears that Black is defenseless. To
Bauer's credit, he is able to find an incredibly way to save his monarch from
instant death. } 6...e5! { A miraculous defense: Black's queen will give itself up
to stave off checkmate and eliminate the pernicious rook. As it turns out,
this merely prolongs the agony. } 7.Rh3+ Qh6 8.Rxh6+ Kxh6 9.Qd7! { If
not for this devastating fork, Black would have been very much alive. As it
stands, Black will lose one of his bishops, and White will then have a huge
material advantage in addition to a decisive attack. The rest is fairly clear
without comments. } ( 9.Rf1?! { would have complicated things after } 9...f5! ) 9...Bf6 10.Qxb7 Kg7 11.Rf1 Rab8 12.Qd7 Rfd8 13.Qg4+ Kf8 14.fxe5 Bg7 15.e6 Rb7 16.Qg6 f6 17.Rxf6+! { The last finesse. White crashes through and
wins even more material. It appears that Bauer was simply too shocked to
resign. } 17...Bxf6 18.Qxf6+ Ke8 19.Qh8+ Ke7 20.Qg7+ Kxe6 21.Qxb7 Rd6 22.Qxa6 d4 23.exd4 cxd4 24.h4 d3 25.Qxd3!? { This is some real chessboard sass!
Payback for not resigning, Mr. Bauer. }
1-0

2- Here we will see a rare but important tactic: Interfering with the opponent's pieces.

White has two passed pawns which are close to queening. One is stopped by the black bishop, the other by the rook. White needs to sacrifice a bishop at the intersection of those two lines, forcing Black to decide which pawn to stop - and essentially "pick his poison".

[Date "????.??.??"]
[Result "*"]
[FEN "8/3P4/4k2P/1B2B3/5K2/8/2b5/3r4 w - - 0 1"]

1.Bd3!! { Tadhaa! Sacrificing the bishop but intercepting both blacks Bishop and Rook. Black must capture this bishop one way or another - but either way, one of the pieces' lines will be closed, allowing one of the pawns to queen. } 1...Rxd3 { If the bishop captures the white bishop then the d-pawn will queen. Black could take the d7 pawn with his king, but then White will take the bishop on c2, and win with his passed h-pawn. } 2.h7 { If White played this before, the bishop could just take it. But now the pawns cannot be stopped since the bishop on c2 is blocked } 2...Rh3 { Black stops one pawn... but it's not enough to hold the position. Black had no way to open the bishop on c2, and stop both pawns from promoting at the same time. A truly amazing position! } 3.d8=Q { The rook could not handle both pawns on its own. In this lesson we have learned how to interfere with the opponent's pieces. In endgames, queening a pawn is crucial, and often it is worth it to sacrifice a piece for that end. }
*

Source: Chess.com


What's the etiquette for giving checkmate on board? I wonder what is considered to be a polite way of giving mate on board. Should one announce the checkmate? If so, should one press the clock after making the move, or stop it, or simply do nothing?

Or should one press the clock silently as if it's a normal move and then wait until the opponent realizes (if they haven't yet) and shakes hands?

This is really a question for fairly low-rated players, who tend to play things out to the bitter end. If you are reasonably strong, the only reason your opponent does not resign earlier is that he thought you played such a good game that he allows you to execute the checkmate (I have done this), or thinks that the final position is beautiful, and saw it coming.

A very good example of the latter is this game between Peter Svidler and Magnus Carlsen at Grenke this past year (2019), where Peter allowed mate on the board. Note the BIG smiles on the faces of both players in this video.

In the end, it is just common sense and human decency: Just be humble, nice, and say "checkmate" politely, and shake hands. Treat the person the way you would want to be treated.

 [Event "Grenke Chess Classic 6th"]
 [Site "Karlsruhe/Baden Baden"]
 [Date "2019.04.28"]
 [Round "8"]
 [White "Svidler, Peter"]
 [Black "Carlsen, Magnus"]
 [Result "0-1"]
 [ECO "B30"]
 [WhiteElo "2735"]
 [BlackElo "2845"]
 [FEN ""]

 1. e4 c5 2. Nf3 Nc6 3. Nc3 e5 4. Bc4 Be7 5. d3 d6 6. Nd2 Nf6 7. Nf1 Nd7 8. Nd5 Nb6 9. Nxb6 axb6 10. c3 O-O 11. Ne3 Bg5 12. O-O Kh8 13. a3 f5 14. Nxf5 Bxc1 15. Rxc1 Bxf5 16. exf5 d5 17. Ba2 Rxf5 18. Qg4 Rf6 19. f4 exf4 20. Qg5 Qf8 21. Qxd5 Rd8 22. Qf3 Ne5 23. Qe4 Ng4 24. Rce1 Ne3 25. Rf2 Re8 26. Qxb7 g5 27. Rfe2 g4 28. Rf2 Qh6 29. Qc7 Ref8 30. h3 gxh3 31. g3 fxg3 32. Rxf6 h2+ 33. Kh1 g2# 0-1


Custom icons/designs for online with other people? Somewhat of a peculiar question/request/search.
Basically, I'm looking for any software/website/etc. where I can play chess with friends however the only caveat is that the icons/designs/board pieces/etc. be whatever I want them to be. Say having a strawberry for a king or a pawprint for a pawn for example. And that one side's icons be different from the other's (as in white king is a strawberry and black king is a shoe).

Hi Anon and welcome to chess.stackexchange.
I would begin at Peter Wong's virtual pieces site. Have a look at this, and if necessary contact Peter, who is very friendly and approachable.
All the best.


Bye-rule in the reykjavic open I am confused about the bye-rule in the reykjavic tournament. If I understand it
 right, a player can take a half point for free under some conditions.

Does anyone know the exact rules ?
What is the sense of this rule ?

The exact rules are on the tournament rules page. If your schedule does not permit you to play every game or you just need some rest, you can can take a half-point bye instead, getting 1/2 point instead of playing. This is pretty much the same bye rule used in every Swiss System tournament.


In the Pirc, bringing a dragon pawn structure fails [FEN ""]

1. d4 d6 2. e4 g6 3. Nc3 Nf6 4. Nf3 c5 5. dxc5 Qa5 6. cxd6

Above you can see the first moves of a Pirc Defense game. To study this opening, I learn with the book "Pirc Alert!" by Lev Alburt and Alex Chernin.

After 4. Nf3, there is a trick which consists of ...c5, ...Qa5 (two pawns are threatened) and ...Qxc5, winning the pawn, ...c5 and bringing a Sicilian Dragon pawn structure, which is very good. But today I played an Internet game (seen above) and White's move 6. cxd6 seems very good. The authors of my book didn't speak about this move.

I had over viewed the position after 6. dxc6 and neither I nor my chess engine. could find any strong reply.

Is the move 6... exd6 strong? What is Black's best reply to 6. cxd6?

Yeah, seems like black just blundered a pawn with c5.
Probably you just mixed up the variation and you really wanted to play:

rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. f4 Bg7 5. Nf3 c5

That is quite a common variation, I looked at 6.dc Qa5 7.Qd4 for white a while back, if I remember correctly. So maybe you should just check your book again, it's unlikely they made such a mistake.


How does "go mate " work in UCI In the UCI documentation, it says

  mate x

  search for a mate in x moves

However, I believe this should say "search for mate in x plies", as plies are used in most of the protocol. I can not find any good documentation for this. Which way does it actually work?

The specification is correct here.

An appropriate implementation would start a search, and then terminate it once a checkmate has been found in x full moves, or 2x plies

  I believe this should say "search for mate in x plies", as plies are used in most of the protocol.

This is not the case.

The way that mate scores are handled is one of the quirks of the UCI Protocol. As it happens, using full moves to describe mates is consistent with the rest of the protocol.

For example, here is the section which describes how scores should be reported:

* score
    * cp <x>
        the score from the engine's point of view in centipawns.
    * mate <y>
        mate in y moves, not plies.
        If the engine is getting mated use negative values for y.

Here, the mate scores must also be reported in full moves, just like the requirement for go mate <x>.

You are, however, right to find this unusual, as most chess engines do represent mate scores in plies internally.


Not knowing what moves to make and feeling lost all the time My tactics and calculation abilities are fairly decent since I practice chess puzzles a lot, but I seem to be lacking in other areas. I always feel uncomfortable in a lot of chess games even though I've honestly played a lot of them by now. As the title suggests I want to gain the confidence and knowledge on what moves to make. I would love to become more adaptable. I love seeing masters being able to play and knowing what to do in any given position and would like to work towards that sort of ability. What should I do?

What you describe is a lack of strategic intuition. Fortunately that can be learnt. All of the following quotes come from Studying chess made easy by GM Soltis.

You need to learn how to spot strategic patterns

  "I only see things quickly if I have seen the position before," GM Yasser Seirawan once said in explaining how he found strong moves so easily.

According to this, developing strategic intuition rests on pattern recognition. When learning tactics, you had:

Theory: e.g. the abstract idea of a pin
Practice: e.g. solving tactics puzzles

This brings me onto...

Learning patterns is about theory and practice

The same thing that was said about tactics can be said for strategic patterns. For example, one pattern might be the exchange sacrifice. It has theory, you can find puzzles, and you can apply it to your games.

Remember that:

  Theory + Practice = Success

Learning patterns is often subliminal

This begs the question, how do I learn these patterns? Well, this is a life-long process.

  Some researchers concluded that the typical grandmaster knows 10,000 patterns (!). Don't worry.

  You can become a pretty good player, perhaps even a master, with a much smaller number of positions in your mental 'pattern bank'.

GM Soltis suggests analysing master games, and gave this specific advice:

  Take note of each middlegame move that is awarded an exclamation point. Try to figure out why it's a good move. If you think you understand why, try explaining it in your own words, as if you were teaching a fellow student.


How to play more chess without your brain tiring It used to be a common problem for me to have very high calculating ability for the first few matches, and then I would make tons a blunders when I play the 10th or more. While for the most part memorizing lines, and having tactics become more inherent is allowing me to play more games, but I still can’t command the high level of analysis I would of at the beginning of the day.

So how do I keep from my brain exhausting?

“Do you drink water during that time? Do you snack or drink soda?”

For the most part, no. I’m in the zone

Following the general rules for staying physically fit are probably a good idea.  Also getting enough sleep before a match. These things always helped me.  Fischer was noted for staying physically fit.  Also he drank apple juice during play.  Getting up and moving around also would seem desirable, since that keeps your blood pumping as well as providing a temporary distraction from your game, which should refresh your thinking.  There are human limits to endurance though no matter what you do.  I've noticed that as I age (I'm 80), I tend to fatigue sooner than I used too.  There's probably no cure for that.


In game 1 of the 2012 WCC between Anand and Gelfand, black ignored his passed pawn advantage. Why? In the first game of the WCC 2012 between Anand and Gelfand, which was drawn, Gelfand had a passed pawn on a6. Could he not have exchanged the major pieces and then tried to win with it?

Why was the passer ignored and the draw accepted?

[Title "Viswanathan Anand-Boris Gelfand,Anand-Gelfand World Championship Match, Moscpw Russia, 5/11/2012"]
[FEN ""]
[startply "48"]

1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.cxd5 Nxd5 5.e4 Nxc3 6.bxc3 Bg7 7.Nf3 c5 8.Bb5+ Nc6 9.d5 Qa5 10.Rb1 a6 11.Bxc6+ bxc6 12.O-O Qxa2 13.Rb2 Qa5 14.d6 Ra7 15.Bg5 exd6 16.Qxd6 Rd7 17.Qxc6 Qc7 18.Qxc7 Rxc7 19.Bf4 Rb7 20.Rc2 O-O 21.Bd6 Re8 22.Nd2 f5 23.f3 fxe4 24.Nxe4 Bf5

There's a great analysis of the game here: 2012 FIDE World Chess Championship: Anand vs. Gelfand - Game 1.

According to the video, it is easy for white to get one of his rooks behind that pawn especially when both players are left with 1 rook, 1 bishop each.


Why should I try to put knights on weak squares when they can be taken easily? Here you can see two weak squares-b6 & d6. That's what my chess book says, and in order to use these two weak squares, one must consider the moves Nf3-d2-c4.

Actually, the story is more complicated (black has the strong reply ...Nc5, but for me it doesn't matter for the moment).

When I searched good ideas for white, I saw the two weak squares, but my thoughts were : "Okay, there are two weak squares, but 1/ Nd7 can take at b6, it is well put at d7 to do that 2/ for e6, Nf6 can move to e8, and moreover Bg7 can move to f8. So the two squares are not useful for me".

As a chess player, could you give me some reasons for not rejecting the positioning of knights or bishops on weak squares? Should I always try to put them on such squares, hoping the exchanges will end with a better position for me?

It is true, that sometimes occupying weak squares with your pieces will just lead to exchanges and no advantage whatsoever. But there is a well known dictum in chess, that "the threat is stronger than the execution".
This means that just threatening to occupy a weak square can severely restrict your opponent's possibilities. Just imagine you brought a knight to c4 and your opponent was set on the idea to either play Nd7xb6 or Nf6-e8 if you dropped your piece into b6 or d6. This would leave him unable to move either knight until you executed your threat. Which in turn would hamper his development, because his bishop cannot move, which in turn means his rooks cannot be connected. And of course you wouldn't oblige him and execute your threat, you would just keep it hanging over his head.

On the other hand, in this specific position, taking the knight on b6 wouldn't solve blacks problems. After you retake with the bishop you actually control the square d8. This is very relevant, because it means that he cannot oppose you with his rooks on the d-line. So, bringing a knight to b6, retaking with the bishop and then taking control of the d-line by doubling your rooks, seems like a valid plan to use the weakness of b6.

Of course these are purely strategic musings, it is always the question whether a plan can be executed tactically.


About forcing a checkmate Could a player sacrifice 3 of his pieces , the opponent's King being forced to take each piece in a sequence of moves where the opponent's King lands on a space where it is promptly checkmated? A kind of 3-move forced checkmate. Could this be done with 4 moves?

White to play and mate in 4, while forcing the black king to capture on each move:

[fen "1r2qrnk/3R1bRp/pp2nBpp/p3P3/4B3/5PPQ/PPP3N1/1K6 w - - 0 1"]

Solution:

   1.Rxh7 Kxh7   2.Bxg6 Kxg6   3.Qf5 Kxf5   4.Nh4#


Brainteaser: What is the one thing a queen cannot do that all other pieces can do? A simple brainteaser - A queen cannot do something all other pieces can do. What is that?

April 18 2014 9:15 PM GMT. EDIT: In this context, by "doing" I mean making a move that leads to the desired result.

I'll have a go at saying the queen is the only piece that cannot reveal a discovered check.


Why do chess coaches encourage their students to play stronger players? I am a 1400 rated player. We have 4 players in our club rated 2000+. If I sat down and played 100 games against one of them, I would lose 100 games. So, how does losing 100 games against one of these strong players EVER make me a better player? [sadly, none of them ever gives a post mortem].

It's partially who the opponent is, and partially how much better the opponent is.

I've gone from ~1750 to almost 1900 in the last year (approximate as ECF grades - 142-158 to those who understand ECF). In that time I've played a lot of players who are appreciably better than me. But not massively better; most have been 1850-2100. That meant I could still give them a challenge, even if I was stretched to hold them for the whole game. In fact a major moment in that improvement was I when I had to play my first ~2050+ player in that period, I was sort of doing OK but a little worse, and then I suddenly realised he a had let me off the hook. This 2050 player had made a mistake! I can not explain quite how much confidence that gave me, and I went on to draw the game, and in fact missed a win along the way. The whole episode set me up for the season, and the game is below.

So that's the first point, good enough so that you see and understand their plans, and that they stretch you, but also not so good that it's wham, bang, thank you mam. The second point is that a lot of the players I have played in this period have been kind enough to go through the games with me. This helped me understand their expectations, and often showed me ideas that I had not even considered. This was coupled with has the 2100+ player at my (small) club helping me, The later in particular clarified my impressions of my opponents plans, helped me identify some of my tactical weaknesses and showed me what both of us had missed over the board.

So for you I suspect 2000+ is a bit rich. But look for players who are

Around 100-300 higher than you
Are kind enough to spend at least a few minutes afterwards going through the games
And then take the games to your trainer to check your opponent wasn't talking rubbish

Anyway here's the game that I referred to earlier. It's at move 19 I had my epiphany.

[Event "A Match in the League"]
[White "Ian Bush"]
[Black "Somebody Scary"]
[Result "1/2-1/2"]
[WhiteElo "148"]
[BlackElo "178"]
[FEN ""]

1.e4 c5 2.d4 cxd4 3.c3 dxc3 4.Nxc3 e6 5.Nf3 Bc5 6.Bc4 Nc6 7.O-O a6 8.Qe2
    ( 8.e5 )
8...b5 9.Bb3 Nge7 10.e5 Ng6 11.Ne4 Be7 12.Nd6+ Bxd6 13.exd6 O-O 14.Bg5 f6
15.Bd2 Nge5 16.Rac1 Bb7 17.Nxe5 fxe5 18.f4?!
    ( 18.Bc2 )
18...exf4 19.Bxf4 Qh4
    ( 19...Nd4! )
20.g3 Qh3
    ( 20...Nd4! )
21.Rfd1 Qf5 22.Bc2 Qf6 23.Qh5 g6 24.Qc5 Rab8?!
    ( 24...Rac8! )
25.Bb3 Rfc8 26.Qe3 Rf8 27.Rc5 Rbc8 28.h4 Na5 29.Rxc8 Rxc8 30.Bxe6+ dxe6
31.d7 Rf8 32.d8=Q
    ( 32.Bg5! Nc4 33.Bxf6 Nxe3 34.d8=Q Rxd8 35.Rxd8+ )
32...Rxd8 33.Rxd8+ Qxd8 34.Qxe6+ Kg7 35.Be5+ Kh6 36.Bf4+ Kg7 1/2-1/2


Assessing an early c4 against white's Stonewall structure I made a horrible decision as black in a game, and I do not understand why it's incorrect.

[fen "rn2kb1r/pp2pppp/1q3n2/2pp4/3P1P2/2PQPN2/PP4PP/RNB1K2R b - - 0 1"]

I played c4, Stockfish considers the position to be + 0.4 after the move. My reasoning: I forever block white's bad bishop behind his blocked pawns, while keeping my good bishop. Since I gain a tempo on the queen, I can move my queen right away to be able to answer the break b3 with b5.

I am also thinking that my position is much better, as white has a hole on e4 and I don't have such a weakness, so I thought I'd capitalize on my advantage by closing up the position.

Stockfish considers this move to be a really poor move, e6 leading to an evaluation of -0.7.

I've had this several time, and it's unclear to me why my move is bad, even though it gives me an inferior position from a superior one.

Is it always bad to close up the position this way, or is it specific to the position ? Why is it bad, because I forever lose my main pawn break ? Or because my "good bishop" has no target and is therefore not really good ?

Good question! The positional priorities in this position do not really lie in whose bishop has more prospects, but rather in the emerging pawn structure, potential pawn breaks, and either side's ability to create targets and holes in opponent's camp.

In short, c4 here is an extremely committal move which should only be played if it can be backed by very strong concrete ideas, which do not exist in this position. Why does the fact that it's committal makes it into a poor choice? It's simply because it resolves white's strategy into something immediate and concrete, namely: to undermine black's pawn chain and create a weak pawn out of c4, and to this end, the almost immediate e4 pawn break is perfectly playable for white without any drawbacks and black has nearly no means of preventing it. So in hindsight, moves such as c4 and similar ones in analogous positions, are only good if you are sure you can stop your opponent's relevant pawn breaks. Otherwise you're creating overly advanced pawns that will eventually turn into weaknesses that you cannot easily parry.
Remember, a pawn is considered to be weak if (all 3 must be met simultaneously):

it cannot move
it is isolated (not defensible by pawns)
it can be attacked.

To summarise: with the unavoidable e4 by white and a4 in reply to b5, the c4 pawn is bound to become a weakness as it meets all 3 said conditions.
Gained tempi and temporarily blocked out bishops are secondary in such positions, unless you have an actual threat following your pawn push (such as, an imminent knight jump to d3!)

More concretely, let's take a look at a few possible continuations as illustrated in the following diagrams:

Left: Early e4 by white  |  mid: early b5 attempt  |  right: e4 blockade attempt

Left: Immediately undermining c4's defense after Qe2, Nbd2, if black takes, c4 is dropping soon and both knights will be well established centrally. And if black tries to sit still, e4-e5 is a threat, leaving black's kingside heavily undefended and white's pawn push is quite straightforward, black will lack space and the ability to create a counter-attack.
Mid: Black prepares for the immediate b5 (with Qc7) in order to reinforce c4 which leads to: Qe2, Qc7, Nbd2, e6, e4, b5, f5! and soon followed by a4. Notice how white's perfectly undermining the entire pawn backbone (e6, d5, b5) of c4.
Right: Black simply tries to stop e4 by blockading it with a knight, but since it cannot really be followed up by f5 (as shown in the diagram), it will easily be challenged with Nbd2 after which black either has to take on d2 which revives e4 again, or lets white take on e4 leaving a ton of light square weaknesses behind along with a permanent knight post on e5. Note that in this structure, black has no prospect for ever landing a knight on d3, leaving the light square control that the overly advanced pawns have secured virtually unusable. Finally, notice that in neither of these cases, black's left with any form of initiative or targets in white's structure to allow for any counter-attack.

Lastly, by not playing c4, you can still entertain a timely resolution of the central pawns in order to either simplify or create weak points in white's centre. And to connect with our discussions, by holding still with the pawn on c5 you are actually stopping white's e4 push as after, say, e6, Nbd2, Be7, e4 you can simply take both on e4 and d4 not allowing white any central control (unlike the case of c4 where white always had clear spatial advantage), and your structure is devoid of weaknesses. If anything, white will be the only side with potential dark square weaknesses. And if white recaptures on d4 with the pawn, then it's a comfortable IQP structure with easy play for black.


AlphaZero’s search procedure I am aware of related questions and great answers on the same topic such as Understanding AlphaZero. My questions are related to the following figure on AlphaZero's search procedure

This figure comes from the Science paper on AlphaZero (Fig. 4, page 4). The search is illustrated for a position from the very nice game 1 AlphaZero (white) and Stockfish (black) after 29. ... Qf8. The rest of note of the figure is as follows

  The internal state of AlphaZero's MCTS is summarized after 10^2,
  ..., 10^6 simulations. Each summary shows the 10 most visited states.
  The estimated value is shown in each state, from white's perspective,
  scaled to the range [0, 100]. The visit count of each state, relative
  to the root state of that tree, is proportional to the thickness of
  the border circle. AlphaZero considers 30.c6 but eventually plays
  30.d5.

I would appreciate some insights regarding the following questions. (Important to note that I am a mere chess player with no knowledge on computer science. I still find this fascinating)

What does represent the 10^2, ..., 10^6 simulations? I am very
confused because in the Supplementary Material they note that
``During training, each MCTS used 800 simulations''.
What does it mean that each MCTS used 800 simulations?
I assume that the value of 60 in the red circle in the 10^2
simulations represents a 60% expected score for white, which is the
    average of all position evaluations. However, the simple average of the 9 moves shown is equal to 61.2. I guess that other moves also considered and simulated. Am I right here?
I assume that for simulations 10^3 to 10^6, they only present an
illustrative sample of the branches. The simulation 10^5 is not
    shown after 34.Rce1 or stopped after 34.Rce1? I guess that each
    simulation goes until an expected score of 100%.

The diagram shows the 10 most visited game states/positions that AlphaZero calculated. It's actually looking at thousands of positions, but they're only showing the 10 positions that it comes back to the most. For your questions:

1) AlphaZero's search algorithm is called Monte Carlo Tree Search (MCTS). The fundamentals of how it works when thinking at some game state:

Pick a move. The way this move is picked is based off an algorithm favoring:

How good a move has performed in past random simulations of it.
How infrequently it has been picked (a move played out less ==> more desirable).

Follow this move to a new game state (i.e., the position that arises when you play the move).
Repeat step 1, for some time limit or depth limit.

The move that has the best average score in all its playouts is the one that AlphaZero picks. There's more involved than this, but the above is the general idea of MCTS. So something like 10^2 simulations for the root node means that AlphaZero performed the above algorithm 10^2 times for that position.

The part where they mentioned "800 simulations" refers to when AlphaZero was learning (before its games with Stockfish). The way AlphaZero learns heuristics on its own (which allow it to accurately evaluate positions) is by playing itself over and over. So, I assume they mean that during this phase of playing itself, each time it thought on what to play in a position, it only performed 800 simulations from a position. The point of this was probably to have time to get more practice games in. Against Stockfish, playing extremely quickly is unnecessary, and AlphaZero may as well use the time it's been given to playout way more such simulations.

2) Explained above.

3) Yes, thousands of other moves are also considered, they just aren't shown in the diagram. Also, even if the 10 states shown were the only ones reached, you couldn't just average their scores out. The reason is that some game states are reached more often than others, and thus have a higher weight in the average calculation.

To illustrate this, assume you only had two possible moves you could play in the beginning of a game: 1.e4 and 1.h4. Looking back at the MCTS algorithm I outlined, playouts/simulations on 1.e4 would happen more often since 1.e4 performs better. However, 1.h4 would also be picked once in a while due to how infrequently you look at it. So maybe you do 9 playouts on 1.e4 and get a score of 60%, while do 1 playout on 1.h4 and get a 0% score. Your odds of winning from the starting position are not (60% + 0%) / 2 = 30%, but rather (60% * 9 + 0% * 1) / 10 = 54%.

4) Yes, only an illustrative sample is shown since they only wanted to show the 10 most visited game states. I'm sure AlphaZero continued the MCTS algorithm far past 34.Rce1.


Is the number of legal chess positions odd or even? Is the number of legal chess positions odd or even? Two positions are not the same if they differ in castling rights (i.e. whether K or R have actually moved) or en passant capability (i.e. whether the move can actually be made) or who has the move.

The number of times position has been repeated is not part of the definition of position for obvious reasons, as is the number of moves since last capture/pawn move.

I don’t have the answer myself. This is hard but doable with a bit of programming I think.

EDIT: The answer so far and the comments are clearly heading along the right lines, although not always correct yet: terrific work. I want to give multiple +1s! I will summarise the key points to help focus the work. Pairing mirrored positions is essential i.e. those which allow triangulation. I term positions which have no mirror image “vampires” :-) Any vampire (except for the starting position) must be immediate offspring of a vampire, so it’s maybe easiest to just count all of them. Someone touched on castling, which is very important. Can you see how to handle castling systematically?

En passant is less important but amazingly there are vampire en passant positions e.g.: r1bqkb1r/2pppppp/8/1pP5/8/8/PPPPP1PP/R1BQKB1R
where White retains at least one castling right, Black has at least queenside castling rights and White can capture e.p.

Odd if you count the initial position and Even if not.

Mirrored positions

Almost any position, including checkmates and stalemates can be flipped by switching colors.

Mirroring the chess board horizontally between 4 and 5 rows, you cannot find a position that colors can be switched and produce an illegal position. So for each position there exists a mirrored position, except the start position.

The challenge would be to find a position that cannot be mirrored.

Non Mirrored positions / Corresponding positions

There can exist positions where it cannot be mirrored due to the "turn that cannot be switched". For its this position, there would be a "corresponding position" that also cannot be mirrored.

e.g. 1. Nf3 Nf6 2. Ng1 Nd5 3. Nf3 Nf4 4. Ng1 Nd3+

its corresponding condition is:

Nf3 Nf6 2. Nd4 Ng8 3. Nf5 Nf6 4. Nd6+

Both cannot be mirrored.

Triangulation

Due to Triangulation, all positions after a pawn is pushed can be mirrored. Non mirrored positions can be constructed only with knight moves, moving only knights cannot produce Triangulation.

Start position

The start position, before any moves, the turn cannot be switched so that black makes the first move.

Calculating positions from knight moves

To solve this for sure, we need to calculate the total positions that arise from only knight moves.


Formulating a Precise Definition of "Space" in Chess Premise

I have always enjoyed playing recreational chess, so I know the basics and some general tactics / strategies. It was only recently though that I have gone more hardcore, so to speak, with my analysis. Namely, I'm taking the "big data" approach by looking at the freely available game logs (which contain hundreds of thousands of games).

I realize there has already been expert machine-learning analysis done with this data and some of it published. However, I'm doing this just because I like chess and I like to dabble with programming. I don't expect to win any Nobel prizes, but I do expect to have fun along the way. Basically I think it's cool to test out the theories or rules of thumb for their effectiveness. Like I said, I'm trying to be humble/realistic about my model specification, and there are probably some things I cannot capture from the data. Some variables/features are easier to formulate than others; which brings me to my question.

I'm trying to figure out if I can create a variable (aka feature) for which player has more "space." Let's say we have this position:

White is said to have a space advantage here. Maybe it's my lack of expertise, and I'm not sure exactly what "space" is being referred to here; I see a few different things going on. The following are my three attempts to explain "space." (bear in mind I am aiming to reduce "space" to something quantitative, hence the nerdy-sounding explanations)

White's pieces have a shorter average distance to the end of the board than black's. White's pawn is all the way on the 5th rank, while black's pieces are closer to his starting position
White has more available moves. Black is looking rather cramped, some of his pieces are getting in the way of each other.
White controls more squares. White's light square bishop controls a longer diagonal than black's, and so forth.

This is the confusing part for me, because I could easily rationalize any of the above items as being "space." Citeris paribus, we could expect a correlation between some of these things, but eventually I have to settle on a precise definition of "space" if I'm to transform chess logs to a quantitative variable.

Question: Is there a precise definition ( be it in the literature or an unspoken but widely understood axiom) of the concept of "space?" Perhaps none of my attempts to explain space are close, and there is a 4th better definition. Either way, please feel free to weigh in.

Note: All I'm asking is a precise definition. You do not have to reduce your definition to the quantitative (unless you want to!)

What is 'space' on a chessboard? the accepted answer to this post hints at my 2nd definition: "space in terms of the number of possible legal moves you have." Is that the overall consensus though?

I define space as a mixture of mobility and squares controlled.

[fen "rbk3br/2p2p2/1pP2Pp1/pP4Pp/P6P/8/4R2K/4R3 w - - 0 0"]

Black is completely lost due to his lack of space.

[fen "8/2p2p2/1pP1kPp1/pP1rr1Pp/P6P/2K5/4R3/4R3 w - - 0 0"]

Black is just as cramped, but his greater mobility and more active king gives him a much better game.

EDIT:  From "Elements of Positional Evaluation" by Dan Heisman.  Section 3.3 Space

So to better understand space, we must once more return to mobility.  What is important to realize is that space depends on mobility; that is, mobility "defines" space.  This means that no matter how the pieces are situated, the player with more space is really the one with more actual and actual global mobility, despite what the pawn structure may seem to indicate.  For example, in a closed position where White's pawns seem more advanced, if Black's pieces, through open files or diagonals, can "point" through and around the pawn mass in some way that gives Black the superior actual mobility, then it is he who may seem to obtain the space advantage.  This is additionally made posible because pieces are not legally bound to stay behind either side's pawns.  Indeed, an over ambitious early push of a pawn mass somethimes leaves one's pieces scattered to the defensive at some later time because the opposition was not effectively reduced in total actual mobility and god behind the advanced pawns.  So, whereas space is an existing and useful term, it does not qualify as a basic element.


Why is the engine evaluating against bringing more attackers in this position? [FEN "r2qk2r/pQpbbppp/n2p1n2/3Pp3/4P3/2N1BN2/PPP2PPP/R3KB1R w KQkq - 0 1"]

This position is evaluated at +6.4l but if I capture with the Bishop (Bxa6) it drops down to +0.8.

Why does the evaluation drop when I make that move?

[Title "AKP2002-moisturiser, 600+5 Rated Rapid game, lichess.org, 4/21/2020"]
[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. d4 d6 4. d5 Nb8 5. Nc3 Bg4 6. Be3 Nf6 7. Qd3 Be7 8. Qb5+ Bd7 9. Qxb7 Na6 10. Bxa6 Qb8 11. Qxb8+ Rxb8 12. O-O-O c6 13. Ng5 cxd5 14. exd5 Nxd5 15. Nxd5 Bf6 16. Nc7+ Kf8 17. Ne4 Bd8 18. Nd5 Bc6 19. Bxa7 Ra8 20. Bb8 Rxa6 21. Bxd6+ Ke8 22. Nc7+ Bxc7 23. Bxc7 Ke7 24. Bd6+ Ke6 25. Nc5+ Kf5 26. Nxa6 Rc8 27. Rhe1 Re8 28. Nc7 Rd8 1-0

Why isn’t capturing with the Bishop good, since it brings more attackers into play, and is hence better move?

Why is the engine evaluating against bringing more attackers in this
  position?

That's not what it is doing. It is evaluating against blundering a draw. After Rb8 your queen has nowhere to go apart from allowing a repetition. If you play Qxa6 you are just a piece and a pawn up for no compensation.

[FEN "r2qk2r/pQpbbppp/n2p1n2/3Pp3/4P3/2N1BN2/PPP2PPP/R3KB1R w KQkq - 0 1"]

1. Bxa6 (1. Qxa6) Rb8 2. Qxa7 Ra8 3. Qb7 Rb8=


How to modify stockfish "skill" with python chess I'm using this library and I couldn't find how to modify that value (skill).
In any case, what I want is to be able to vary the level of difficulty of stockfish using python chess.
Thanks.

Send an UCI command Skill Level. Something like setoption name Skill Level value 10.
EDIT:
https://python-chess.readthedocs.io/en/v0.25.0/uci.html. Please look at setoption.