The original PGN standard was created and published in 1994 by Stephen J Edwards. Here is a copy of his original standard: Portable Game Notation Specification and Implementation Guide.

Here it mentions the use of "%" as an escape string:

  There is a special escape mechanism for PGN data. This mechanism is
  triggered by a percent sign character ("%") appearing in the first
  column of a line; the data on the rest of the line is ignored by
  publicly available PGN scanning software. This escape convention is
  intended for the private use of software developers and researchers to
  embed non-PGN commands and data in PGN streams.

So, % in the original specification was for "the private use of software developers".

By 2001 this was already being used with Stephen Edwards dropping out from maintenance of the standard as remarked in this supplement for enhanced PGN:

  Steven Edwards, the author, appears unfortunately to be no longer
  involved with  PGN and there is now no defined means of arbitrating
  and implementing proposed  changes. There is also a huge body of
  software which implements the current  standard and would break in
  various ways if it were changed.

The document's main proposal is the further definition of how "%" should be used for embedding commands in PGN. This was targeted at time commands:

  3.2 A generalised format for embedding commands in comments.
  3.2.1 Position An embedded  command may occur at any position in a standard PGN comment, ie  between { } . For example: {Optional leading
  comments [%clk 1:05:23] optional trailing comments} where  [%clk
  1:05:23]  is the embedded command string.

  3.2.2 Structure The command string is structured as follows.

  A leading tag of [% A command name consisting of one or more
  alphanumeric characters. A space character. Either a single parameter
  or a comma delimited list of parameter values. A closing tag of ]

%csl and %cal are relatively new commands following the 2001 extension definition. I found references to their use on the ChessTempo website in their Comment Markup Annotations Chapter 18. PGN Viewer BETA Version

  The PGN viewer supports some special markup that allows arrows, square
  highlighting and mini-board insertion to be rendered on the board or
  move list.

  Arrows To have a move show arrows on the board when it is played, you
  can embed the following type of string into a comment on the move:
  [%cal Gc2c3,Rc3d4]

  the '[' and '] characters are the start and end of the arrow markup.
  The %cal indicates you are requesting a coloured arrow to be drawn.
  This example will draw two arrows a Green arrow from the c2 to c3
  squares, and a Red arrow from the c3 to d4 squares. The colour letters
  supported are R=Red, G=Green, Y=Yellow and B=Blue. Square Colouring To
  have a move highlight squares on the board when it is played, you can
  embed the following type of string into a comment on the move: [%csl
  Ra3,Ga4]

  The %csl indicates you are requesting a coloured square. This example
  will highlight two squares, a3 will be highlighted Red, and a4 will be
  highlighted Green. The colour letters supported are the same as used
  by the arrow annotations.

It looks like Chesscafe and lichess are following this beta version.


How do I get Stockfish to show notes like it does on Lichess?

Stockfish is an UCI chess engine, so you shouldn't mess up with the engine. You will need to write a new chess GUI.

Useful links:

https://www.chess.com/forum/view/general/chess-engines-amp-gui-uci
How do I use the analysis output of a UCI engine?
What is the optimal way to use Stockfish programmatically?
How to get position evaluation with UCI?


What is the main idea of 7.Qf3 in the Sicilian Taimanov?

Main ideas:

Castling long as soon as possible
The Qf3 will most often move to g3 to pressure g7 and d6, and possibly help the break e4-e5.
Both central files are left for the rooks to apply maximum pressure (unlike after Qd2 or Qe2 developments)


Candidates 2013: could Ivanchuk have drawn?

Other than the catchall rule mentioned by D M, Article 11.1: The players shall take no action that will bring the game of chess into disrepute., I don't think there is a rule that prevents such scenario directly.

Also I believe that it is pretty much impossible to set up such rule, because there are too many possibilities. Also it would be very difficult to enforce it. Think of the following:

You would have to prove intent, which seems rather difficult.
Games at this level are rarely played out to a completely won position. It would have been easy to either make a small blunder to equalize the position, or just to claim that you evaluated the position incorrectly as draw.
The outcome of one game can affect many things. Apart from the direct points, it might also affect tie-break scores or the Elo rating (which could be relevant for instance for participation in the candidate tournament). Whatever the outcome of the game somebody will always be unhappy and could claim that the result is match manipulation.
If there was such a rule every time you make a blunder you would be under suspicion of match manipulation.
Last round quick draws in tournaments are pretty common as are not-fought-to-the-end games in team competitions (if it secures a win for the team for instance). Seems like match manipulation to me as well, and not much is being done to prevent it.


Moving the queen early in the game - beginner

The main issue with developing your queen early is that it is a very valuable piece, so pretty much any time your opponent threatens to take it, he is threatening to win material. (Contrast with developing your knights, say; if your opponent threatens to take it, unless he's threatening to take with a pawn, he is often just really offering an equal exchange.)

The best way to take advantage of your opponent's early queen development is to exploit this by attacking it while developing your own pieces. If you can combine development with attacking the queen this way, you'll get all your pieces onto useful squares while he wastes time moving his queen around, and you'll be in much better position to do something in the middlegame.

A simple example of this is 1.e4 e5 2.d4 exd4 3.Qxd4 Nc6, developing the knight while attacking the queen.


Why have engines not increased top rated chess players' Elo?

I think they certainly have increased their ELO, but more importantly, their overall chess strength. ELO is only a rating relative to others in the pool so it may tend to go up more slowly if everyone in the pool gets better, which they have collectively.

First, you need to take an average of the top players, rather than look at just two incredibly special players, Kasparov, and Carlsen, and their peak ratings. Fischer was a total anomaly for his time, and again, you cannot base a lot on one person. Humans probably have a limit mentally much the way runners will eventually hit a speed wall that they cannot break. It is the Bell Curve in action: Easy to make progress in the middle, but harder on the end.

ChessBase, and the first strong engine, KnightStalker (aka Fritz 1.0, renamed at version 2.0) came out in 1990, and the Internet was still in its infancy. In January of 1990, there were only two players over 2700, Karpov at 2730, and Kasparov at 2800. Today, there are 37 players over 2700, and of those, three are over 2800.

I have been playing for a long time, and anyone, who knows my handle, has seen me watching relays of the top tournaments on ICC for more than 20 years, and I can say that it is not just inflation from having actually watched the level of play improve over the years. Players at the Master-level, including even normal Masters, are MUCH better now due to the tools available today than the tools available when I first became a Master.

When I first started playing, all we had was books, and a local club. Today, I can logon virtually any day, and play a GM. I was also a ranked tennis player as a teenager, and I can tell you from that experience, playing better competition makes you better, so being able to logon and play stronger players than ever has increased the overall level of play. In addition, we now have ChessBase, and a database of about 8.3M games that can be sorted efficiently and studied. We also have engines, as noted in the question, and they certainly have also added to our chess knowledge, and fundamentally changed how the top players prepare. Lastly, I mentioned books, and as an avid collector (I had 1800 at my peak), I can tell you that even the quality of the material in books is on another level since when I started.

I cannot tell you what proportion of all these advances have played toward X-number of rating points increase, but I can tell you that without a doubt, they all have lead to players at the top levels, and even down some, being much better overall.


Yes there is a chess league in the US, but it does not have the sponsorship you see in Europe. Check the USCF website, and this more specific site http://uschessleague.com/


How can I find the endgame probability based on the opening?

You can do something like this in SCID, which is a free program. It takes a little effort, but it's not too bad.
First, load the desired database. Then use a filter to select only games from the opening of your choice. You can filter either by a position, or by ECO code, to get the desired opening. Note how many games meet the filter criteria.
Next, use the "Search for material or board patterns" filter feature. You can use the "Common Endgames" button on that screen, or you can select your own criteria. Make sure to select the "AND (Restrict filter)" option. Hit the Search button, and the filter will be restricted to only games which meet your selected criteria. Note how many there are, and with some basic math you can calculate what percentage this is.
Repeat this for all desired endgames.

You can also use the Opening Report feature to get some quick endgame probabilities. Put the desired position on the chessboard, and then run the Opening Report from the Tools menu. This does, however, include all games in the database with that opening, regardless of whether they really have an "endgame" or not. It will count a Scholar's Mate as a "Q, R, BN" endgame since those pieces are all on the board.


In an opening tree on ChessBase, how can we fix the statistics so that transpositions are not taken into account in the total number of games?

Unfortunately, many of the statistical functions of the Opening Book feature in ChessBase have been unreliable in every version I've owned.

For example, after the Caro-Kann line 1. e4 c6 2. d4 d5 3. e5 Bf5 4. Nf3 e6 5. Be2 Nd7 6. O-O h6 7. Nbd2 Ne7 8. Nb3 Qc7 9. Bd2, the opening book PowerBook 2013 shows this table:

Move       N     %    Av  Perf
          15  76.7  2409  2283

9...Bh7    8  56.3  2433  2494
9...g5     6  83.3  2405  2233
9...Nc8    4  62.5  2393  2335
9...a5     2  50.0  2561  2564
9...Be4    1 100.0  2414  2315

Well, first off, you'll notice that the number of games in the total (15) has no relation to the number of games in each variation given (a total of 21).

Second, if you do some simple arithmetic, you can work out that the average White win percentage is actually 66.7%, not 76.7%, as reported.

Well, then, let's ignore the overall position total statistics, and move on to examining a line item. Let's look at the 9...Bh7 line, which this table says was derived from 8 games, with a White winning percentage of 56.3%

If you make that move, you get a new table. Since we're now at the new position, the position statistics at the top of the new table should read the same as those from the 9...Bh7 detail line of the parent table from the prior position, right?

Here's what they actually say:

Move       N     %    Av  Perf
           8  56.3  2545  2484

Not bad, right? The first two stats agree... but the Average ELO and Performance ELO numbers are off by 100 ELO in the 1st stat, and 10 ELO in the 2nd.

And here's the full table for the new position

Move       N     %    Av  Perf
           8  56.3  2545  2484

10.a4      4  75.0  2455  2513
10.Bb4     4  62.5  2557  2537
10.Rc1     2  50.0  2650  2591

Again, the total # of games is unrelated to the # of games in each of the continuations.  And this time, the White winning percentage works out to 65%, not 56.3%.  And the position's Performance ELO is clearly not the average of the continuations' Performance ELO. It should be 2538, an error of 50 ELO.

I picked a ready example from a game I was looking at a few minutes ago, but any game will do to demonstrate this problem.  I frequently find that when I try to choose a move from an apparently winning continuation that the the detail data from the resulting position just doesn't support the apparently "winning" statistic. In some cases, it could say White has as much as a 60% winning percentage for the continuation, and then in the next position none of the further continuations has a percentage higher than 50%. Simply put, it's nonsensical.

Now, here's where it gets interesting:
I have set my Reference Database as the database of games that was supplied with PowerBook 2013 (PowerGames 2013). PowerBook 2013 was generated by ChessBase using all of the games from PowerGames 2013, and only those games.

I can now open the Reference window pane, and it will look up the statistics from the games in that database. They should be identical to the stats shown in the Opening Book pane, but they're not.

In fact, the Reference statistics for the 2nd position (after 9...Bh7) show the following:

10.Bb4     4  62.5
10.a4      2  50.0
10.Rc1     2  50.0

This is where the total statistics in PowerBook 2013 are coming from! The total number of games = 8 (correct), and the average performance = 56.25% (correct)!

In fact, in the PowerBook 2013 continuation stats there appear to be 2 extra games where 10.a4 was played (and which White apparently won), but they don't appear in the Reference database stats at all, and they aren't factored into the PowerBook 2013 totals stats.

It doesn't really matter whether this is a problem inherent in the commercially-sold books from ChessBase, or in how the ChessBase database software uses/calculates/displays the statistics. Simply put, there's a defect here that's been present since at least ChessBase 6.0, and hasn't been fixed at late as Version 11 (the one I'm using).  Just watch out for it when you try to use an opening book to pick a line based on its purported winning percentage.  The best approach is to use the Reference Pane, or at least double-check the continuations for a couple of further moves.

Personally, I now use the Reference window pane for this purpose, and put up with the slight lag required to update the stats for every new position in the game.  I use an AMD Quad processor at 2.9 GHz, so if you have something less powerful, you might feel the pinch a little more.

I'm not excessively critical of the ChessBase software in general; I use many of the features quite effectively. But a few of them have known faults you should know how to work around.

Another example: Try using a position search in a database; ignore the results. Then, edit the position within the search filter (add, move, delete pieces, whatever), make a note of the new position you're now searching for, and run the search again. Save the resulting list of games.  Now, reset the search filter completely (I suggest closing and reopening the database as well). Finally, set up the (altered) search position again from scratch, and run the search a 3rd time. The results from the 2nd (edited position) and 3rd (fresh position) searches should match. They frequently do not.  I've noted many cases where the fresh search filter returned many more games than the edited search filter.  I have no explanation for this, but I no longer edit the position in the search filter.  I always create a fresh position (usually by copying and pasting from a game window I set up for the purpose).

Hope this is helpful!


After 1.Ne7 Black has 1...f5, stopping the immediate 2.Bf5#.


What was the role of the second in top level matches?

What was the role, the duties, etc. of the second (e.g. GM Ray Keene
was Korchnoi’s second in the 1978 World Championship match vs. Karpov)

What it most definitely was NOT was writing a book of the match ready to rush into print the moment the match finished as Keene did.
The way it was supposed to work was that after the time control was reached at move 40 one of the players would seal a move. The players would then go back to their respective hotels with their seconds and perhaps discus a few lines. The principal would then have a meal and go to bed. The seconds would then stay up all night analyzing the position and coming up with a list of variations for the principal to look at and learn when he got up the next morning.
On nights when there was a new game starting the next morning it was the job of the seconds to prepare opening lines based on the opponent's repertoire for the principal to look at the next morning.
Sometimes, in the build up before a world championship match, a player would hire a strong player for a secret match to try out ideas in a realistic match atmosphere. Botvinnik famously did this as did Anand.

is this figure still present in contemporary top level chess?

Very much so.
Today the main job of the second to do the dogsbody work of opening preparation for the principal. Part of this may be preparing the player to play against a particular opponent's repertoire. Jan Gustaffson has famously helped Carlsen with opening prep as this is his main area of expertise as a chess player.
The other more interesting part is to come up with new ideas in opening lines. This requires creativity and computer skills with engines because they play a big role. This doesn't automatically require GM level chess ability. Nakamura has famously employed the same sub-2200 player, Kris Littlejohn, since 2008 simply because Littlejohn comes up with many creative opening ideas, is very good at investigating them with engines and gets along well with Nakamura on a personal level.
There is more on the Nakamura-Littlejohn relationship in this Chessbase India Facebook video and this episode of Ben Johnson's Perpetual Chess Podcast.
There is more interesting information about seconds in this post.


Carlsen is 21 years young and is currently the highest-rated player in the world. He scored a win against Karpov and a draw against Kasparov at the tender age of 13 (Reykjavik Rapid 2004), and was the second youngest player to become a grandmaster (at the time he did it). Things like that are enough to brew confidence, garner world championship expectations, and draw superficial comparisons to a similarly precocious talent like Mozart.

I imagine that his main advantage over his current closest rival Aronian in terms of grabbing attention is just the fact that he is 8 years younger. And whereas, say, Sergey Karjakin is only a year older than Carlsen, and is the one who still holds the record for becoming the youngest grandmaster ever, he simply doesn't have the sort of tournament record that Carlsen does, especially in the highest-class tournaments of the last few years. (Note that Karjakin does have impressive recent wins like Wijk aan Zee 2009, Tal Memorial 2010 and Bazna Kings 2011; but Carlsen's success of late has been such that that trophy shelf pales in comparison.)

Anyway, assuming the upcoming world championship cycle goes through as planned, then Carlsen will have his chance to justify all the chatter and expectations. But I'll be rooting for Kramnik or Aronian myself :-)


Is targeting the f7/f2 square in bughouse a good rule of thumb?

https://www.youtube.com/channel/UCcKXwA_lo3Zpz3_Mc-WVLtw is the YouTube channel of Helmsknight.  She is a strong player who plays with Nakamura, Seirawan, and many other high rated players.  Interesting is that all these players tend to castle before starting an attack.

Just like normal chess, starting an attack on this (these) square(s) is often a good idea.  However, I used to take advantage of this common attack and have both boards play passively.  Soon my opponents would be down a couple of pieces (on each board sometimes) and no resources to continue the attack.

For a better understanding of proper use of resources, Crazyhouse is the variant.


A few thoughts, but as I expressed in the comment, I don't think this question will have a single good answer.

Based on general opening principles in regular chess, I would not sacrifice a central pawn, because that might reduce control on the center.

Secondly, in order to speed up development, I would sacrifice a pawn that already opens lines or diagonals for the development of rooks/bishop/queen.

Based on my experience playing Fischer random/chess960, I found positions quite convenient where the bishops are on a1, b1, g1 or h1, so that they immediately attack something once the pawns moved away.

Combining all this, one possible position could be

8/8/8/8/8/8/PPPPPPP1/BBKRQNNR w - - 1 1

Here I go for an atack on h7, g7, and also all pieces could support any operations in the center of the board.


Why doesn't Lichess' Stockfish suggest this bishop sacrifice?

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

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

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

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

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


How to use Polyglot opening book bin file

I have every reason to believe your approach is wrong and will lead to disaster. I'm saying it as someone who make softwares to work on Polyglot books (www.smallchess.com).

You are strongly advised NOT to do all the hard works like what I did before. Just wrap the C++ Polyglot code in your C#! Your time should be on your C# engine, not this.

Polyglot, although open source is not something you would like to port to C# unless you are super motivated. Why? Polyglot has bunch of hash keys. Screenshot on my source code:

There was never any good documentation on Polyglot, it existed mainly in source code. Today, not many people really know how that does (including myself). I understand only part of it, by reading source code.

That was the comment I wrote to myself when I started using Polyglot many years ago:

    /*
     * A PolyGlot book move is encoded as follows:
     *
     * bit  0- 5: destination square (from 0 to 63)
     * bit  6-11: origin square (from 0 to 63)
     * bit 12-13-14: promotion piece (from KNIGHT == 1 to QUEEN == 4)
     *
     * Castling moves follow "king captures rook" representation. So in case
     * book move is a promotion we have to convert to our representation, in
     * all other cases we can directly compare with a Move after having
     * masked out special Move's flags that are not supported by PolyGlot.
     */

Polyglot works like this:

Given a position, convert to a hash key. I have my screenshot for the conversion

Use the key to locate an entry in the book using binary search
Read the entry from (2)
Extract the chess move like:


Which chess variant has the largest board?

Taikyoku shogi should be a good candidate. It was created in the 16th century, so it's a variant that has actually been played. The board size is 36x36, and it has 209 different types of pieces.


Jeremy Bierema has written a Swiss pairing program and put it on Github. You could look at the code there which is in C++.

At any stage in the tournament you have to have a list of forbidden pairings.

The first, obvious entries are pairings that have occurred previously. The second, banning 3 whites in a row, is ww v ww since one of them will have to be white giving www. Similarly bb v bb is forbidden. Then the white/black imbalance, so 2 v 2 and -2 v -2 are forbidden since in each case one player will end up with a 3 or -3 imbalance.

So, for each player you need to keep track of previous opponents, colour sequence and colour imbalance. This gives you the information to know which pairings are forbidden. In the last round you should also perform the forbidden pairing check for colours and pair with this in mind if possible. If not then you can ignore colour restrictions in the last round only.

The "previous opponent" forbidden pairings are cumulative. The "colour" forbidden pairings change from round to round as the players' colour sequences and imbalances change.


Which is the most CPU efficient chess engine?

If I were going to do this, I'd choose Stockfish, Fruit 2.1, and Crafty for no reason other than their high quality is proven.  Then I'd compare and contrast the techniques, algorithms, and choices made by each.

These aren't easy programs; it would be a lot of work to gain a true understanding.


does it mean that Be3 is the best 6th move in the Najdorf for white
  and does it mean that normal play with 6... e5 is very dangerous for
  black?

"No" is the answer to the first question and "Not really but in any case, as hoacin points out, there are plenty of reasonable alternatives for black" is the answer to the second question.

Look, whether it is true or not, the vast numbers of cynical ordinary club players like me strongly suspect that every time a game like this was played it was preceded by the players meeting in the bar the night before and agreeing a draw and then picking their favourite "forced draw" variation.

When challenged the players will come out with standard BS along the lines of "Well, I spent hours preparing the X variation [say first 5 moves above] because I know my opponent plays that line a lot. All my preparation was based around move 6 and I expected he would play move y [obviously a different choice from the drawing variation] and when he didn't I had to fall back on the repetition line".

It is complete hogwash. Everybody knows it. But if both players have decided, for perfectly good reasons [tournament situation, tired after previous long hard game, minor illness - cold, stomach bug, etc., opponent is a close relative] that a draw is what they want then there isn't much anybody can do about.


Are there any official rules for Bughouse?

I found two sources. For fans of the USCF they have produced their US CHESS SCHOLASTIC BUGHOUSE RULES but not a grown up version that I can find.
The rather more serious Czech federation holds an annual bughouse championship in conjunction with their regular national championships as part of an annual chess festival. They publish their formal rules here.
These appear more serious and handle more difficult problems like formalizing storage of captured pieces and the way they are handled:

1.6   When a piece is captured, the captured piece is passed to the partner stuff-place immediately after the move is completed, not later than before the player's next turn. A player's "stuff-place" is an area reserved for pieces that the player can drop on the board. The player's stuff-place must be between his opponent's eyes and the player's hands. So the stuff-place is usually between board and player's hands.
Before the game the players and arbiter should agree on the position of the stuff-place
1.7   A player cannot attempt to hide pieces from the opponent. During the whole game the players shall manipulate the pieces in such a way that both opponents are able to see all pieces. Only when captured pieces are transferred to partner's stuff-place or in the moment when player is moving or dropping piece on chessboard, a piece may be partially hidden in a players hand. However it must be clear to his opponents which piece is partially hidden and this moment must be as short as possible.
1.8   a) If a player hides pieces in an improper way (rule 1.7), his opponent (or partner of his opponent) is entitled to warn him to "show pieces".
b) If a player drops a hidden piece, his opponent may restrict its use by the message "invisible", e.g. "invisible bishop". The opponent may then immediately start the player's clock and force him to make another move.
c) A piece restricted in this way may not be used until the opponent allows (by the message "bishop visible now", for example). The opponent should allow it as soon as possible, in good sportsmanship.
d) If a player repeatedly hides his pieces, his opponent (or partner of his opponent) may claim "repeatedly hiding" and the arbiter may impose some sanction. (rule 9.4.)
e) If a piece is hidden through no fault of the player, and this drastically alters the game, the arbiter may order a new game.

Contentious issues around simultaneous checkmate are also handled:

1.9   When player is checkmated after taking any piece then if his partner has the move, he may drop this piece as his last move.
1.10  If both games finish at the same time, the results on both chessboards are counted up; the team which wins on both chessboards wins the bughouse game. Otherwise the bughouse game is draw.

2.2a The bughouse game is draw when player is taking a piece, then (in the next opponent move) is checkmated, his partner's move is in this moment, his partner is by dropping this piece (before his time is out) checkmating opponent or making draw by achievement of 3x repeated position (See 2.2.b).

There is no mention of stalemate for the obvious reason that a player can always put a piece on from the "stuff-place" or wait for a piece from his/her partner.
Also no mention of 50 move draw rule because, let's face it, pieces are always going to get taken and pawns are going to be moved and recycled and very quickly.
There is, though, a 3-fold repetition draw law.


Why not fight off a bishop on row 5 with pawns?

Here are a couple of relevant questions and answers that might help to explain why the bishop move happens:

Morphy Defence in Ruy Lopez
Why is the Ruy Lopez such a common opening?

In summary the main points seem to be that:

Black loses as much time chasing the bishop as White does retreating it
White can gain a long-term advantage from Black's weaker Queen side pawn structure

As you might expect in such a popular opening though it's very finely balanced for both sides.

If as you say you are not seeing a6 and b5 in the games you're looking at, you might be looking at games where Black plays the Berlin Defence: 3... Nf6. This is quite popular at the moment in very high level games.

If you want to see some games where the pawn move a6 is played, "putting the question to the bishop", here's a link: http://www.chessgames.com/perl/chessopening?eco=C70


Which opening is most defensive as black?

This is a subjective question, so I'll give a subjective answer. In my opinion, the Hippopotamus Defense is the most defensive opening. Here's a typical Hippopotamus structure -

   [FEN "r2qk2r/pbpnnpbp/1p1pp1p1/8/2PPP3/2N1BN2/PP2BPPP/R2Q1RK1 w kq - 0 9"]

Black doesn't even move a pawn to the 4th rank! All of Black's minor pieces are developed on the second rank and Black keeps his pawns on the third rank. Essentially, Black plays a waiting game for a while, and tries to provoke White into doing something concrete and then Black reacts accordingly.

P.S. Since you're a beginner, I would advise NOT to use this opening. Yes, it is the most defensive opening, but if you're afraid of playing 1...e5 then you ought to first correct that instead of trying to play something else! Even with 1...e5, Black can reach defensive setups.


First off: I suspect White resigned due to the material disadvantage rather than some immediate mating threat. Having said that, I don't see any reason not to give check on c8 and try to setup some threats here as White, since it seems like Black gets checkmated:

1.Qc8+, Ke7 2.Rb7+, Kf6 3.Qf5+, Kg7 4.Qxf7+, Kh6 5.Qg7#


Is castling legal regarding rooks passing over attacked squares?

It is still possible to castle if the rook passes through squares that are attacked(under control by opponent's rook e.g. as you say), it's only in the case of the king that such scenario prohibits you from castling.

Have a look at the post Cleveland has suggested in the comments.

Here's an example anyway:

[Title "O-O-O"]
[StartFlipped "0"]
[fen "2bk2nr/p1p2ppp/2p5/2p5/2P1P3/2N5/Pr3PPP/R3KB1R w KQkq - 0 1"]

1.O-O-O+


Maybe it's about having a Knight on e5, which cannot be dislodged easily with pawn moves. I think it's not so significant though, because black can still at least exchange it against the knight on b8, which could come to d7 or c6. d7 might prevent the exchange o black's bishop against the knight on e5.
If white manages to get black to exchange on e5, white will have a pawn on e5 most likely. Maybe a point is to still have a pawn there, although white didn't move e4-e5 earlier?
I don't really see how Ne5 is really that helpful to be honest. It doesn't even look that interesting to me or much different than other positions.


What are some of the chess databases in the public domain that can be used for commercial purpose?

I don´t think chess games are copyrightable, as they´re just a collection of facts, so games of chess are not considered by the courts to be anyone´s property.  I would say that you are free to comercially reproduce a game, as long it´s just that, the moves played in that game.
To put in perspective, if you took a screenshot of the result of a videogame, for example Civilization, or if you recorded a song in Guitar Hero, then that would be the intellectual property of the creating videogame company.  Following that pattern, any PGN would be the legal property of whoever invented chess, but I believe the copyright may have expired by now.


Is there a way to ask stockfish from the command line if a position is "quiet"?

I don't think there is anything like that, and it'll never be implemented.

If you insist, you may want to look at how Stockfish does quiescence search. A "tactical" position would mean a dozen of long series of recursive calls. A "quiet" position would mean otherwise. However, this is a very dirty trick which might not work very well, you'd also need to do some programming.

There're other ideas, such as looking at the average branch factor, number of captures in the principal variation, the distribution of the scores... None of which is absolutely satisfactory.


Find a KNP-KQ endgame in which Black loses

[Title "White plays and wins (note the position after 2 Kg6)"]
[FEN "4N2k/8/6PK/q7/8/8/8/8 w - - 0 0"]

1. g7+ Kg8 2. Kg6 Qb6+ 3. Nf6+ Qxf6 4. Kxf6 Kh7 5. Kf7 1-0

If Black stops 3 Nf6# with Qf5(g5,h5)+ then 3 Kxh5 and the Ne8 still holds
the Pg7 so White soon wins.  The bottom edge of the board barely prevents
Black from turning the tables with 2 ... Qa0+.


What is the idea behind the touch move rule?

If you're allowed to touch a piece, you can also pick it up and land it on another square, look how the new position would look like, and return it to it's original square if you don't like the new position. Repeat this over and over again, and it becomes very annoying for your opponent.

This explains why the rule might exist, but not since when. I do not know the answer to that question.


It is really a matter of taste over "better".  I like the tempo gain that dxc4 gives.  Usually the pawn is on c4 before Bf1-d3, but when Bf1 develops, as in your game, it loses time capturing on c4.  Additionally, the Bishop sucks on c4 and will likely move yet again.
Black will have time to play c5 with a nice game.


I'm looking for informations about calculating ELO (FIDE) rank

Here is a blog post about elo calculation.

You can find the rules for determining the correct K-factor on this site, which also contains an official Fide rating calculator to check your results against.

Here is the official description of the rating calculation (based on tables instead of formulas).


well, having seen f5 in my game, I would probably reply with h4 and then bring a knight from b1 to f4 and a rook to g3 (if necessary). I remember something like this being discussed in one of the Dvoretsky's books as a response to early f5. I don't think black has any potential of developing a king side play after that.
Of course, in short time control everything is playable, especially if white is expected to premove Bd3 and 0-0


Which currently active chess player tends to play complicated positions?

Alexander Morozevich probably obtains the most consistently complicated positions of any >2700 player, although he has fallen off some since the mid-2000s.

Baadur Jobava is probably his rightful successor, but a recent string of horrible tournaments pushed him under 2700 and he is now sitting at 2699.


It is called a clearance sacrifice:

In a clearance sacrifice, the sacrificing player aims to vacate the
square the sacrificed piece stood on, either to open up lines for his
own pieces, or to put another, more useful piece on the same square.


Is it always a good idea to trade a bishop for a knight if the enemy has castled and is forced to disrupt his castle's pawn structure?

As always with such questions, the correct answer is "It depends on the position!".

For example if your opponent doesn't have an e-pawn, you will create isolated doubled pawns, which are generally quite weak. But in a 4 vs 3 rook endgame, with all pawns on the kingside this structure is actually better for black than f7-g7-h7 because it is harder for white to create a passed pawn.

Taking gxf6 will often weaken the black king, but only if you are actually able to attack him. If you have all your pieces on the queenside he might just play Kh8, Rg8 and start an attack on your king!

So, this is a weakening of his structure, but you have to be able to take advantage of it. Otherwise a bishop might just be more useful than a knight.


What are some beginner to advanced openings or variations I could use?

It is hard to answer a repertoire question with little supporting information. On that basis, I would recommend 3 things:

Complete the quiz on chesspersonality.com. At the end you will receive recommendations on openings, for White and Black, based on your answers
To stick to one opening as White, and have 1 response as Black for 1. e4 and 1. d4. The other common opening moves, 1. c4 and 1. Nf3 are quite rare at a  beginner level, and are chosen because they usually transpose into 1. e4 or 1. d4 openings anyway
Look at some opening videos on YouTube, such as those by Dereque Kelley. If you like the look of an opening, try taking the main themes into your next game


Stockfish is considering a move in a book by GM Mihail Marin as a blunder

Mihail Marin simply missed that 1.Ng6 is winning, even faster than 1.Qg6. During opening analysis, and even during a game, sometimes when you find a satisfying continuation you forget to follow Lasker's advice and look for an even stronger one.
This is a slight mistake in his analysis, but his evaluation of the variation remains correct (White is winning, even faster than he thought) and I see no reason not to continue studying his book and learning from it.
No chess book is completely void of analysis mistakes. If this is the worst one in the book, then the work is still very trustworthy. However, I encourage you to keep your good habit of checking the author analysis, with your own mind and with engine: First, to prevent falling for a bigger hole in a flawed variation if there is one ; Second, to better understand and remember the positions.


I know you're a FIDE Master :), so I suppose you're more interested in this question from a teaching perspective.

The simplest way to understand a checkmate with King and Rook vs King is the idea of the rectangle of the opposing king. Consider this position-

Here, the Black King is restricted by the White Rook in this giant rectangular area of the chessboard. For simplicity, I am not considering the area restricted by the White King, which would be like this -

A simple way (I'll deal with optimizations later) to checkmate is to ensure that this rectangle gets smaller and smaller, so that the Black King is pushed to a corner of the board (more visual representation below with diagrams).

    [FEN "8/8/8/8/4k3/8/8/K6R w - - 0 1"]

     1. Re1+ Kd4 2. Kb1 Kd3 3. Kc1 Kd4 4. Re2 Kd3 5. Kd1 Kd4 6. Kd2 Kc4 7. Re3 Kd4
     8. Ke2 Kc4 9. Rd3 Kc5 10. Ke3 Kc4 11. Ke4 Kc5 12. Rd4 Kc6 13. Rd5 Kb6 14. Kd4
     Kc6 15. Kc4 Kb6 16. Rc5 Kb7 17. Kb5 Ka7 18. Rc6 Kb7 19. Kc5 Ka7 20. Rb6 Ka8 21.
     Kc6 Ka7 22. Kc7 Ka8 23. Ra6#

1. Re1+ Kd4

2. Kb1 Kd3 3. Kc1 Kd4 4. Re2 Kd3 5. Kd1

5...Kd4 6. Kd2 Kc4 7. Re3 Kd4

8. Ke2 Kc4 9. Rd3

9...Kc5 10. Ke3 Kc4 11. Ke4 Kc5 12. Rd4

12...Kc6 13. Rd5

13...Kb6 14. Kd4 Kc6 15. Kc4 Kb6 16. Rc5

16...Kb7 17. Kb5 Ka7 18. Rc6

18...Kb7 19. Kc5 Ka7 20. Rb6

Ka8 21.Kc6 Ka7 22. Kc7 Ka8 23. Ra6# 1-0

Of course, with this method, the one mistake that White must avoid is stalemate -

Rb7?? stalemate!

Optimizations and Tricks.

More experienced players can get to smaller rectangles quicker by looking further ahead.

One trick is to trap the king in a smaller rectangle if it comes too close to the rook. For this, White also has to use the king more actively.

   [FEN "8/8/8/8/4k3/8/8/K6R w - - 0 1"]

   1. Re1+ Kd4 2. Kb2 Kd3 3. Kb3! Kd2 4. Re4! Kd3 5. Rc4

Another trick is to give a rook check when the kings are in opposition.

   [FEN "8/8/8/2k5/8/2K5/8/4R3 w - - 0 6"]

   1. Re5+!? (1. Rd1!) Kd6 2.Kd4

This trick is not necessarily optimal. In the above example, White can actually mate faster with the move 1. Rd1!

   [FEN "8/8/8/2k5/8/2K5/8/4R3 w - - 0 6"]

   1. Rd1! Kb5 2. Rd5+! Kc6 3. Kc4

The above optimization is also made possible by the rook-waiting-move trick. If, in the above position, instead of going to c6, the Black king tries to escape via a4, then the following checkmate is possible.

 [FEN "8/8/8/1k6/8/2K5/8/3R4 w - - 0 7"]

 1. Rd5+ Ka4 2. Rc5! Ka3 3. Ra5#

One more idea is to use king-opposition (in combination with the rook) to push the enemy king behind.

 [FEN "8/8/8/2k5/8/8/2K5/4R3 w - - 0 4"]

 1. Kc3! (1...Kd5 2. Re3!) Kc6 2. Kc4! Kd6 3. Re4

Combining these different ideas, here are two of the most optimal mates possible from the starting position -

   [FEN "8/8/8/8/4k3/8/8/K6R w - - 0 1"]

   1. Re1+ (1. Kb2 Kf4 2. Kc3 Ke5 3. Re1+ Kf6 4. Kd4 Kf5 5. Re4 Kf6 6. Re5 Kg6 7.
   Ke4 Kf6 8. Kf4 Kg6 9. Re6+ Kg7 10. Kg5 Kf7 11. Re5 Kg7 12. Rf5 Kh7 13. Kf6! Kg8
   14. Rh5 Kf8 15. Rh8#) 1... Kd4 2. Kb2 Kd3 3. Kb3! Kd4 4. Kb4 $3 Kd3 5. Kc5! Kd2
   6. Re4 Kd3 7. Re5 Kc3 8. Rd5 Kb3 9. Rd3+ Kc2 10. Kc4 Kb2 11. Rd2+ Kc1 12. Kc3
   Kb1 13. Kb3 Kc1 14. Rd3 Kb1 15. Rd1# *


I used to play such as white before I got educated...

Well, it is not that bad and on the plus you don't need to learn much or any theory.

There are two possible responses from black which I found quite unpleasant to play this against.

If black does not play an early d5, he has the option for a King's Indian setup where you play d6 and e5. So black is directly fighting you on the dark squares. IMO the stonewall is almost unplayable in this case.
If black uses a standard setup with d5 and develops the bishop to f5 quickly, you end up with weak light squares and a bad dark squared bishop. Exchanging the light square bishop on d3 is not something you really want either. Black would typically put pawns on c5, d5, e6, the bishop to f5 and just develop normally.

Because of this you should stay flexible and consider other options depending on what black does. Two popular plans involve fianchetto of either bishop.

With the kingside fianchetto (g3, Bg2) you could go for a King's Indian Attack with early f4. Here you would want to play d3 and e4 eventually.


Why shouldn't I play c5 in Queen's Gambit Declined as white?

In most cases White doesn't want to play c5 in such positions because it takes the pressure of the black center. Yes, it cramps the black queen side a bit but it allows Black to play e5 at some point and break the center instead, freeing their c8 bishop and more. With the white pawn on c4 that is more difficult, sometimes d5 may just be hanging after e5 and even if not White can take on e5 and d5 to give Black an isolated queens pawn with not much compensation. After c5 Black has no such problems and can freely play e5, banking on a well defended d5. If anything it is White then who has to be careful, the d4 might become slightly weak, or after a capture on e5 the c5 might get into trouble later.
Of course as with everything it depends on the position. E.g. if Black already committed to a6 like in a Chebanenko Slav then c5 may be a good move as then b6 really is quite weak.
(also I should give a disclaimer that I'm not a d4 player so take this with a grain of salt)


What you're doing here is not correct and definitely not what a chess engine is designed for. You're running multi-pv analysis with many many lines. Multi-PV with many lines as in in your example is exponentially slower than a single-PV analysis. In an N multi-PV analysis, the engine would need to examine the first PV then ignore it for the next best PV. And this continues until all PVs are examined. This is very slow when you do it in iterative deepening where the search tries deeper by each iteration.

Also, the position is tricky for an engine because it has too many captures. When you're in a very tactical full-blown position, the engine would need to expand its qsearch so to get to the bottom of the search tree.

In summary, what you're doing here doesn't make any sense. You'll need to scale down your lines.

Your lines are not sorted is the fault of the user interface and not the engine.

Please read http://www.cruxis.com/chess/manual/index.html?game_play.htm for the Tactical Mode. You'll need to send that UCI command to Houdini.


Which 20th century grandmster had the highest draw percentage in their career?

World Champion Tigran Petrosian was known to be almost impossible to beat.  He's your man.  Study his games and legacy.

Per Wikipedia, he lost 1 out of 129 Olympiad games.  Olympiads are top-notch tournaments and the score is over 20 years of play.  He's not a flash in the pan.

In his 8 Euroteams competitions (held every three years from 1957 to 1983) he lost -0- out of 52 games.  His team won the competition every time.

Then I started poking around in chessgames.com and I started looking at win/loss/draw ratios.

I made a list of all world champions since Botvinnik, including the weird ones where FIDE lost control.

The three players with the best win:loss ratio (in order): Kasparov (6.62), Fischer (4.87), and Petrosian (4.38). Kasparov dominates. (Only Karpov and Botvinnik are in the same class as these three.)  I expected Kasparov and Fischer to be in this list. I was surprised that Petrosian was there, to be honest. But we see that he was very much able to score the win. He's about like Fischer in this regard.

The three players with the best win:draw ratio, in order: Fischer (1.7), Botvinnik (1.22), and Kasparov (1.02). Fischer dominates. No other players are in their class.  I attribute this to an uncompromising aggressive desire to win.  No half measures. Petrosian was not afflicted with this mentality.  If it did not fit, he did not force it.

The three players with the best draw:loss ratio, in order: Petrosian (6.74), Kasparov (6.52), and Kramnik (6.25).  Spassky and Karpov trail. No one else is close.  This means that even if you had an advantage over one of these players, you'd have to work like mad to score the full point.

The three players with the best win+draw:loss ratio, in order: Kasparov (13.14), Petrosian (11.13), and Kramnik (9.73).  Each is dominant over the next. Karpov and Spassky follow Kramnik closely.  This reflects upon the difficulty of scoring the full point.   An opponent would twice as likely to nick a full point off Carlsen than Petrosian.  Ouch. (I think this is a statistical fluke due to Carslen's age...but it makes a good story.)

Finally, while I did not list it, Petrosian has one of the lower win:draw ratios.  He was more than willing to accept a draw if he could not see how to secure the win.  Other players with a similar win:draw ratio do not possess Petrosian's compensating win:loss ratio, however.

This rather defines his style, I think.  You can see here a player who will defeat you if you aren't careful. He is patient and takes few chances. If you get ahead of him, he'll likely wear you down, into a draw.  And if you err, he'll crush you.

edit - fun facts for the world champions...

In the 4 ratios I looked at (w:l, w:d, d:l, and w+d:l)...

Kasparov is the only player who made the top-3 in all 4 ratios.
Petrosian is the only player who made the top-3 of 3 ratios.
Fischer and Kramnik both have two top-3 honors, but also each have a bottom-3 honor.
Botvinnik is the only player with a single top-3 honor.
Topolov and Carlsen each have three bottom-3 honors.
Carlsen excepted, the three champions from the weird FIDE years (Ponomariov, Kasimdzhanov, and Topalov) have the lowest W+D:L ratios.  There is a marked just in score difference between them and the next lowest scored player (Smyslov).  Find the clue.


Why isn’t Black forced to prevent e4 in this Queen’s Indian Game?

There is a huge difference here, and that is first, that you will get the bishop pair for white's big center, but also that your Bf6 is beautifully placed for they typical black move in the Queen's Indian, c5, which will cut across the a1-h8 diagonal. Also, the white center can be successfully attacked.

In the other example from the other question, cxd4 does not break up the center at all, and there was still the danger to the black king with e4-e5. You can see that in your game today, e4-e5 allows the queens to be traded, and will actually leave e5 vulnerable.

 [FEN ""]

 1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. Bg5 Be7 5. Nc3 (5. Bxf6 $6 Bxf6 6. e4 d6 7. Nc3 Bb7 8. Be2 c5 {Breaking up the center or if d5, making the Bf6 a monster.} 9. d5 Qe7 10. O-O O-O 11. Re1 Nd7 12. Qc2 Ne5 {And black is very comfortable.}) 5... d5 6. e3 Bb7 7. Be2 Nbd7 8. O-O dxc4 9. Bxc4 O-O 10. Ne5 Nxe5 11. dxe5 Ne4 12. Bxe7 Qxe7 13. Nxe4 Bxe4

By the way, while Be7 is not technically wrong, it is not in the spirit of that opening, and is a bit passive. Here is a typical line fighting for, and keeping control of e4.

 [FEN ""]

 1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. Bg5 Bb7 5. Nc3 Bb4 6. e3 h6 7. Bh4 g5 8. Bg3 Ne4 9. Qc2 Bxc3+ 10. bxc3 d6 11. Bd3 f5


Is there a way to watch blitz championship currently on chess.com on youtube?

The stream from earlier today is available to be viewed here.

There will be another broadcast tomorrow, but that will be a separate stream, with a different link to view (and the link won't be available until tomorrow).


What happens if I push a pawn to the 8th rank and press the clock before promoting?

"If the player has moved a pawn to the furthest distant rank, pressed the clock, but not replaced the pawn with a new piece, the move is illegal."
Source: Fide Laws of Chess taking effect from 1 January 2018 at 7.5.2.

If a move is illegal, it's illegal in Blitz, too. What can differ between Blitz and classical is what the penalty for an illegal move is.

Previously, in blitz/rapid a player making an illegal move would instantly lose the game.

However, January 1, 2018 revisions to FIDE Laws of Chess acted "to equalize the rules for classical chess on the one hand, and rapid and blitz on the other, with regard to the penalty for making an illegal move."

  Before, in both rapid or blitz an "illegal move" (which includes moving with two hands, or not making a move and pressing the clock) would instantly lose the game in case the arbiter intervened or the opponent stopped the clock. Now, in the first instance it will lead to a time penalty and only if a player does it again, he or she loses—just like in classical chess.

Source for quotes on 1/1/2018 change: Peter Doggers, New FIDE Laws Of Chess For Blitz, Rapid Still Not Perfect


Is it possible to extract "sub-scores" from an engine's evaluation?

What about?

The eval command will do what you want. However, it's not useful for chess learning. They are just static evaluations. What you're after is more like extracting features from the analysis. Stockfish doesn't have it.


Would a classic full time armageddon tiebreaker be balanced?

That wouldn't make any sense. In a long game between two 2800+ players, a draw is always very likely. Carlsen and Caruana understand exactly how to steer a game to a draw.

Whoever gets Black would have a winning advantage before the game even started.


It is not checkmate because Black can interpose a piece to block the check from the bishop: move knight or queen to e6.

It's still only a miniscule delay for the inevitable.

[FEN "1rk4r/1p6/3p3q/Q1pPbRnP/p1P3B1/P6P/1P4R1/7K w - - 0 1"]

1.Rf7+ Ne6
(1...Qe6 2.Qc7#)
2.Qc7# 1-0


If your opponent's pieces aren't well positioned and/or their king is in danger, it's important to refrain from exchanging pieces (generally). The reason is that each of your pieces has a higher relative value than their opposites. They tend to control more space, or have more opportunities to prove dangerous to the enemy king.
Assuming it's White to move (even though it was Black to move in the game), a good choice would be 1.Nf5, at which point SF 11 gives over a +6 evaluation. Here you can aim to trap the g5-bishop with h4. If 1...Kb7 or 1...Kb6 is played, enabling ...Bf4 (due to the Black queen's protection), you could further control the f4-square with 2.Rf1. Now it looks like Black is unable to save the bishop from h4.
An alternative 2nd move is 2.Qf3, preparing to take on d5 and get dangerously close to Black's king. If this happens, the queen and knight could end up conducting a decisive attack together. The fine point is that if Black protects the pawn with 2...Qg8/2...Qd8, f4 is no longer contested so 3.h4 wins the g5-bishop.
EDIT - so it's actually Black to move in the position. White's general plan is still similar: going after the g5-bishop. Nf5 could be played soon (maybe on the next move). Black could try exchanging queens via ...Qe8-...Qe4, but then after doing so White could play g3, keeping the g5-bishop from escaping via f4. Another idea is 1...Qf8, when after 2.Nf5 Black might play ...Bh6 if needed. But now White could dramatically activate the c3-bishop with Be1-Bg3+. Pushing a4 is another idea, further increasing the pressure on Black.


Is it legal to hit the clock with piece, captured or otherwise?

I feel this is legal. I'm using FIDE rules.

This is the rule that describes what happens with a capture:

  3.1.1 If a piece moves to a square occupied by an opponent’s piece the latter is captured and removed from the chessboard as part of the same move.

There's nothing there about what happens to the captured pieces, other than they are removed from the board.

Now, of course somebody will argue that this rule exists:

  6.2.3 A player must press his clock with the same hand with which he made his move. It is forbidden for a player to keep his finger on the clock or to ‘hover’ over it.

And there it says "with the same hand". But you also have to remove the captured piece with that hand, and once you've done that you have to press the clock, and there is no requirement to let go of the piece. I argue that this rule is intended to be used against people who move a piece with one hand and press the clock with the other, not against using the piece that you happen to have in your hand.

Of course, there is an opportunity for bad behaviour, by hiding pieces in your hand so that the opponent doesn't notice he is behind in material (IMO that's that opponent's fault, look at the board not at the removed pieces), or worse, hiding the piece that the opponent wants to promote to. Or by simple distracting the opponent by constant fiddling with pieces in your hands.

But there are already rules against distracting the opponent, there is also the umbrella rule against "bringing the game of chess into disrepute", and when you want to promote but don't immediately spot the piece it is always acceptable to stop the clock, call an arbiter and have him fetch the piece for you. That is enough ammo to use against bad behaviour.


The two main things I do to avoid time trouble are:

I write down the remaining time for each player after every move. This both keeps me very aware of the amount of time I have left, and lets me know how much time I have spent thinking so far on the current move, so I can take appropriate action if I've already been thinking for 5 minutes. I also try to have a few checkpoints; for example, if the first time control is at move 40, I try to have at least half my time left at move 20.
This one is harder: in a non-critical position, I am willing to take less time than I'd like and just make a decent move in 2 minutes instead of spending 10 minutes looking for the best possible move. Of course you don't want to do this when the difference between the best move and second-best move is very large, which you don't know in advance, so you have to use your experience and intuition.


The base version is for everybody, all Windows users. The other versions are built for specific hardwares, and should outperform the base version if you have the hardware.

Try the bmi2 and popcnt versions, if they crash on you fall back to the base version.


Yes, resigning a clearly lost game is indeed considered good behaviour. Sometimes not resigning is considered unsportsmanlike!

It makes no difference on the result of the game whether you resign, are checkmated, or lose on time - a loss is a loss. In any rating system I've ever heard of, the method of losing doesn't make a difference.

It's just that people don't like wasting time when they're 100 % sure that their opponent will win the game almost effortlessly with no danger of making a serious blunder.


Are the best engines good enough that they will always win against the best humans?

TL;DR - that ship has sailed.

EDIT - one user claims quite rightly that the ELOs between different populations should not be compared. And by different populations, he means FIDE ELO and whatever ELO the chess engine people are using. He is correct. Therefor, we cannot say that a 2800 ELO is the same as a 2800 other-ELO. But in the current case, we do have enough information to know that the other-ELO are in the ballpark. Giving the paucity of information available, what follows is my best guess.

Bear in mind that there have been few ratable games between humans and chess engines. Comparing ELOs is fraught with peril. That being said...

The best engines on non-customized but stout hardware are rated well above Magnus. Stockfish and Komodo are estimated to play with the strength of a 3381 player. At his peak, Magnus Carlsen achieved a rating of 2882, the highest rating ever achieved by a human.

The way ELO works is that a 400 point ratings difference means the lower rated player has virtually no chance of winning the game.

The difference between the current Stockfish rating and peak-Magnus' rating is 499 points, well over the 400 point limit.

When Kasparov lost a match to a computer (the first) he wasn't hailed as the Heroic Defender of the Realm. It hurt his reputation to a degree. Engines are far better now even on non-custom hardware. Professionals have little incentive to play them. And engines are no fun to play.

I think it is fair to say that Magnus would have no chance of winning a tournament-type match against the best Stockfish or Komodo implementations.

For this reason, while we can't know for sure, but the time has probably already arrived - only a fluke would save Magnus from losing every game.  And bear in mind, this is on commercial-commodity, not custom, hardware. (Deep Blue, the machine that beat Kasparov, was on corporate-sponsored custom hardware, as a comparison.)

Here, enthusiasts have rated many engines:

Remember, these ratings should probably not be directly compared to FIDE ELO ratings.

Fun fact! According to this page, in 2009, a cell phone achieved a rating of 2898 (higher than Magnus' highest), against humans, at a FIDE category 6 tournament. Had it been human, it would have received a "GM norm".

And according to this page, in 2007 and 2008, there were a few human-engine matches, and Rybka gave odds (eg pawn-and-move) to the human. A 2700-ish player won these matches but it was not a slaughter. The player lost a normal (non-odds) match to Rybka. The best Rybka engine is currently rated as the 15th strongest engine.


(Rook + Knight vs Rook) vs (Rook + Bishop vs Rook)?

TL;DR: Rook + Bishop offers significantly more winning chances against a lone Rook (38%) than Rook + Knight (only a few %).

Full answer:

'Secrets of Pawnless Endings' by John Nunn mentions the following about the ending with the Knight:

  [the stronger side] has far fewer winning chances than in the ending of R+B v R and in practice the ending is often agreed drawn immediately. Top-level wins are very rare, but there was one famous example in J.Polgar-Kasparov, Dos Hermanas 1996 being one of the exceptions.

The chapter about R+B v R mentions 74 games of which 28 (38%) were won by the stronger side.

The book I already mentioned, and 'Fundamental Chess Endings' by Lamprecht and Müller, cover these endings. For the Bishop ending, they both explain the main defensive techniques, the so-called Cochrane defense and the Second Rank defense, and some key positions (discovered by Philidor in the 18th century already) which can be won by the stronger side, e.g. this one.

The endgame with the Knight is easier to hold in general. The defending side needs to prevent their King being forced to the edge; if that does happen, the chances of winning are actually greater than with the Bishop. An advantage for the defending side is that the Knight is worse in protecting its own King from checks by the defending Rook. If the defending King is confined to the edge, his rook should either pin the Knight or give annoying checks; this resembles the Cochrane defense in the Bishop ending. Some winning positions were published by Centurini in the 19th century.

In general, endgame databases are very helpful, at least for analyzing winning positions. For draws, they are trickier to use, because they don't tell you how difficult it is to hold a certain position. Especially the Bishop ending contains many 'marginal' positions which can only be held with secure play.


How can I make a chess exhibition exciting for 'laypeople'?

I've been to a lot of events that have featured the live-action chess game. It's usually a big hit with people not normally into chess. Make a giant chess board with paper or tape or whatever and bring costumes along for people to act as the pieces. You'll want to run quick games that way so the people don't get bored. And be prepared for the kids to get antsy and run off. Having some backup players on the wings to take over can be helpful.

Try to work up a crowd with a couple "main events", and steer people around to the shorter things like your tactical idea on the side-lines. More often than not, a big crowd in one part will create interest for others, even if they wouldn't be interested normally.


Is it possible to draw this endgame where I blundered my queening pawn?

There is a third way to draw this endgame - sacrifice your rook for two pawns. With only a knight, Black will not be able to checkmate you.

So from move 14 on, you should keep checking the king, or, if the king doesn't protect c2, attack c2. Black will never be able to escape.

A possible sequences of moves:

[FEN "7n/8/3R4/8/8/2kp4/2p5/2K5 w - - 0 42"]

1. Rc6+ Kb3 2. Rb6+ Ka4 3. Rc6 Kb3 4. Rb6+ Kc4 5. Rc6+ Kd5 6. Rxc2 dxc2 7. Kxc2 draw


Why is the Cozio defense in the Ruy Lopez not played more often and what's white's best try to defeat it?

The major reason is that it is played so rarely is that if white does not comply and take on c6, the Ne7 is poorly placed blocking the Bf8, and if the knight goes to g6, that just does not look like a good square either. In addition, it does not really help get in d5 since white gets there first with d4, or it just loses a pawn. Since that is not possible, the Bf8 must go to g7 where it just seems out of place with what most Spanish players are used to, and prefer. Also, most of the lines are still slightly better for white, even if they are subtle in nature.

There are three moves that are played on move four with a very high frequency: 0-0, c3, and Nc3. Nc3 seems like the best to me since it thinks very prophylactically, and stops d5 for a long time. In addition, the winning percentages for each move are 53.1%, 56.8%, and 62.6% respectively pre the Mega 2020 database.

I tend to like double e-pawn positions that white has more space because black has a d6 pawn. You can then eventually post the Nc3 on d5, cramping black further. I am going to propose that you play 4.Nc3, and aim for such a position since the plans for white are aggressive, and clear. In addition, I like positions with more space, in general, since I think that it makes it harder on your opponent in a practical game.

Despite my recommendation, I am going to add in some of the other lines so you can look at them, and decide if you prefer any of them. The other lines are also quite good, but they are also much more nuanced, and require very patient, and precise, positional play, compared to the main 4.Nc3 line I am proposing, which involves either a direct attack, or bringing the rooks to the center, and slowly advancing the kingside pawns.

 [FEN ""]

 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nge7 4. Nc3 (4. c3 g6 5. d4 exd4 6. cxd4 d5 7. exd5 Nxd5 8. O-O Bg7 9. Re1+ Be6 10. Bg5 Qd6 {Transposes to 4.0-0.}) (4. O-O g6 5. c3 Bg7 6. d4 exd4 7. cxd4 d5 8. exd5 Nxd5 9. Re1+ Be6 10. Bg5 Qd6 11. Nbd2 O-O 12. Ne4 Qb4 13. Bxc6 bxc6 14. Qc1 Rfe8 15. Bd2 Qb6 16. Nc5 Bf5 17. b3 {With a very positional game revolving around the control of c5.}) 4... g6 (4... d5 $4 5. exd5 Nxd5 6. Nxe5 Nxc3 7. dxc3 Qxd1+ 8. Kxd1 $16) 5. d4 exd4 6. Nxd4 (6. Nd5 {Another main line.} Bg7 (6... Nxd5 $2 7. exd5 Qe7+ 8. Kf1 Ne5 (8... Qb4 $2 9. Qe2+ Ne7 10. Bg5 Bg7 $2 11. Re1 $18) 9. Qxd4 Bg7 10. Bf4 f6 11. Re1 $16) 7. Bg5 h6 8. Bf6 Bxf6 (8... Kf8 9. Bxg7+ Kxg7 10. Bxc6 Nxc6 11. Nxd4 $16) 9. Nxf6+ Kf8 10. Qd2 $14) 6... Bg7 7. Nxc6 $5 (7. Be3 O-O 8. Qd2 d5 9. O-O-O dxe4 10. Bxc6 Nxc6 11. Nxc6 Qxd2+ 12. Bxd2 bxc6 13. Nxe4 Bf5 14. Rhe1 Rfe8 15. Ng3 Be6 16. b3 $14) 7... Nxc6 8. Be3 O-O 9. Qd2 d6 10. O-O-O $14


It seems to me that the Slav defense is what you are after.

It has similar pawn structure to the Caro-Kann / Scandinavian defense, and no weak pieces ( Black gets ...Bf5 early ). Notice that it is theoretical, and that it can be dodged with clever move order, like 1.c4 c6 2.e4! d5!? 3.ed cd 4.d4! when you have Caro-Kann ( Panov-Botvinnik attack ).

You could also try King's Indian defense, as pawn structure is similar to White's in Closed Sicilian (there White goes for f4, light squared bishop is fianchettoed, d3+e4 center formation, here you aim for ...f5 and bishop is also fianchettoed, d6+e5 center formation ).

It really depends on your style, please tell us more about your criteria for defenses against 1.d4 so we can offer better answer ( closed/open game? highly tactical/positional? space advantage/counter-attacking? ).

Sorry for posting this as an answer, but the content is too big to fit inside a comment.

I will transform this into answer, if it solves your problem, or if you update your post with more details as I have said above.


Why don't people play the Englund Gambit?

A part of it has to be that white doesn't have to keep the pawn.
[FEN ""]
1. d4 e5 2. dxe5 Nc6 3. Nf3 Qe7 4. Nc3 Nxe5

4.Nc3 is actually the most popular move in lichess database. Black Queen is placed a bit strangely on e7, it is blocking the development of the dark-squared bishop and not supporting the d-pawn if it wants to move to d5. Black can double white pawns with Nxf3, but white has plenty of activity to compensate for it. White has many promising continuations, but here is one:
[FEN ""]
1. d4 e5 2. dxe5 Nc6 3. Nf3 Qe7 4. Nc3 Nxe5
5. Bf4 Nxf3+ 6. gxf3 Qb4 7. Qd2 d6 8. e4

This position is not exactly a gambiter's dream, since white is much more active, and also stockfish gives it 1.5.


Stalemate

Stalemate is a situation in the game of chess where the player whose turn it is to move is not in check but has no legal move. ... In popular usage, the word stalemate refers to a conflict that has reached an impasse, and in which resolution or further action seems highly difficult or unlikely.

In the above position, your opponent had no legal moves but was not on check hence stalement. The objective of chess is to;

The object of the game is to checkmate the opponent; this occurs when the opponent's king is in check, and there is no legal way to remove it from attack. It is never legal for a player to make a move that puts or leaves the player's own king in check.

So if this is not achieved there is no winner unlike in checkers where you can win if your opponent has no legal move


You can try for Zukertort Trap in the Lisitsin Gambit line.
After 1. Nf3 f5 2. e4
the trap-line is Ng5
then if the opponent sticks with his pawn on f5, and pushes d5, then, simply play d3, followed by exd3 and then play Bxd3, and notice that the king has serious weakness on one of its diagonals.
Now, if opponent replies with Nf6, then the best option is Nxh7. If black captures with Nxh7, then Bg6(check), Kd7 and then Qxd5 (mate).
You can also go for, Bxh7 instead of Nxh7, also its winning for you, after Nxh7, you play Qh5, Kd7; Nf7, Qe8, Qxd5 (mate) and if black captures the bishop with rook, then you take it with the Knight, then Nxh7, and Qh5, checking the queen and picking up the Knight.


Alternatives to the paid analysis on chess.com

If you have a lichess.org account you can analyze both games you played yourself there or games you imported. I think currently the limit is 25 of your games played in the site and (not 100% sure) half of that for games you did not play on the site, so either games from other players or ones that you imported.
Not sure exactly which stats you want however it gives you the number of blunders, mistakes and inaccuracies, as well as your average centi pawn loss which is a rough measure of how good your play was on average. Then you can for example use the "Learn from my mistakes" feature to see the positions where you made a mistake, and try to find a better move. Or you can simply look at the computer line in that position.


In this case, I will have to quote from the FICS FAQ (http://www.freechess.org/Help/HelpFiles/fics_faq.html):

  39.My rating is over/under inflated.

  Don't worry!  Ratings are all relative anyway, not absolute. Compare your
      FICS rating only to other FICS players, not to ratings from other groups.
      Comparing your rating on FICS to a person's rating on another server or
      in a chess federation is not a valid comparison. FICS has a different
      rating system and a different player community than other organizations.
      Therefore your rating here is unlikely to match your rating somewhere
      else.

  40.I have a rating on FICS. What would my rating from in-person tournaments be?

  Ratings on FICS are not comparable to those gained from
      real life tournaments because they measure play against a different group
      of people under different playing conditions. Some users have higher
      ratings in real life, some have lower ratings.

In your question, you say FICS Elo rating, but the Elo rating system (http://en.wikipedia.org/wiki/Elo_rating_system) is a system of its own and FICS might not even be using it for its ratings. FIDE does, for sure! Also, comparing two rating systems is dubious since the opponents you meet, the time controls you use and the initial rating you get and the rating system you use will differ! But comparing the FIDE blitz rating with the FICS rating might be more valid. In this case, my guess would be that the FICS rating will be higher than the FIDE blitz rating. And I base this on absolutely nothing!


What would be a minimum set of parameters that needs to be specified in order to avoid ambiguity in pairings?

The minimum would be to have just one rule.  Do your first round pairings by sorting players according to their ID number... and then, in the second round, do it again.  If you don't have any rules about repeating colors, scores, or meeting the same player twice, there's no ambiguity possible.  If you don't want to flip a coin to see who gets White, just declare that the highest-rated player gets White.

This would, of course, be ridiculous and unfair.  But it would be unambiguous and minimal!

  Now if all of these rules/parameters have been set, is there still any ambiguity left? Or conversely, is it possible to satisfy all rules or would some get precedence in case they contradict each other?

Assuming you have sane rules (not like the one I described above), there are pretty much going to be rules which have precedence over other rules.  If White wins more often than Black, there's no way you can have a color preference rule and a same-scores rule without one taking priority.  Under FIDE Dutch rules, there is a minimum set of "absolute" rules, and many more "quality" rules with specified precedence.

  For instance FIDE specifies that no player should play three games in a row with the same color. But if there are only two players (who both have played the last two rounds with the black pieces) with 7 points left who are therefore going to be paired. What is going to happen then? Is the FIDE rule of three same-color games going to be violated or are they going to be paired with other players first?

The following is considered an "absolute" rule:

  non-topscorers with the same absolute colour preference shall not meet

Assuming that 7 points is a "topscorer" (has over half the maximum possible points), then pairing the people with the same absolute color preference would not violate the absolute criteria.  And then, "minimize the Pairing Score Difference" has a higher priority than "minimize the number of topscorers or topscorers' opponents who get a colour difference higher than +2 or lower than -2" and "minimize the number of topscorers or topscorers' opponents who get the same colour three times in a row."  So the answer is usually going to be that the rule of three same-colored games will be violated, so as to comply with the higher-priority rule that the pairing score differences be minimized.  (It's possible that the various absolute rules would require another resolution, of course.  For example, if the two players with 7 points had already played each other, they wouldn't be able to play each other again.)

Under the FIDE Dutch rules, with the exception of the coin flip at the beginning to determine colors, the pairings are very deterministic.  They have rules like:

  All the possible transpositions are sorted depending on the lexicographic value of their first N1 BSN(s), where N1 is the number of BSN(s) in S1

which means the organizers can't ordinarily decide things like which possible transposition to take.  There's not any wiggle room.

The exception is if it's somehow impossible to comply with the absolute rules:

  If it is impossible to complete a round-pairing, the arbiter shall decide what to do.

The only scenarios I could think of where this might happen is an extremely low turnout, or a mass walkout.  (If you have 8 rounds and 8 players, you can't avoid playing the same opponent twice.  Or, if everyone who played White quit  before playing, after the first round everyone would ineligible for the bye because they'd already had a forfeit win, and after two rounds you'd also have non-top scorers that all had the same absolute color preference.)


Black wrecks white's pawn structure

Black gains in development since he's trading an undeveloped piece for a developed one.

Although the center is sill fluid, black's dark square bishop is currently a "bad" bishop. in the short run, white's knight is the more active piece.

It removes the support of the c-pawn which opens up some tactical possibilities and also forces white to do something in the center rather than sitting back.


There are three ways to get out of check.

Simply move the king away.
Block the check, or place a piece in between the king and the opponent's attacking piece.
Capture the piece that's checking the king.

All of these cases are dependent on the fact that immediately after you make your move, the king is not in check. Therefore, you may capture the queen so long as the king is no longer in check after you make your move.


As was stated in the answer to this post made by D M, one idea of capturing in this manner is to open up the g-file for white's rooks to attack black's king. In the game this proved to be a very potent idea, and in general it's a good idea to open up lines for one's rooks against the enemy king if one intends to attack it.

But there is another point to letting the e-pawn hang and that is to gain some tempi for the attack. When black's queen spends one tempo on capturing on e3 with check, white responds by playing Kh1 (a move that white wants to make in order to clear the g-file for the rooks), so while black used a tempo to make a move that does nothing to bolster their defenses, white made a move that is crucial for the coming attack (gaining 1 tempo, relatively speaking). Next white improves the position of the rook on c1 by going to e1. Once again, this is done with a gain of tempo, since black's queen is exposed on e3 and needs to spend one tempo moving away. This way white manages to get two "free" tempi to make his position more ready for going on the attack while black had to strut around with their queen, arguably doing nothing to bolster their defenses.

So the pawn sacrifice had a two-fold purpose here, I would say. First, by capturing with the g-pawn white opens up an important line of attack against black's king. Secondly, by investing the e-pawn white gains some free tempi to use in order to make their position more ready to go on the offensive against black's king.

In general, material count is only one of many factors in evaluating a position, and while it may be the most obvious it is not always the most important one. In this example, Carlsen judged that his superior piece coordination and black's kingside weaknesses were more important positional factors than the material count, and seeing how the game went it is difficult to argue that his judgement was off.


Guidelines for preparation for a Blitz tournament

Know your openings!

You didn't mention time control, but it doesn't matter, you just may not allow yourself to waste precious time on opening.

Avoid sharp, theoretical lines if you can not memorize them fully.

I usually avoid such openings because if you face a novelty/variation you haven't seen so far, there goes precious time on thinking for a move that will "keep me in the game", and usually you will end up caught in the endless loop of searching the only move that "keeps you in the game".

Take solid lines that give equal chances, do not worry about possibility of a draw. Since this is blitz, people make mistakes/blunder more often, and do not forget that time trouble is a huge factor here.

Your job is to play the opening as fast as you can, without any mistake, so you can get a playable middle game with equal chances and concrete and simple play/counterplay.

In the middle game, simplify a little, so you can protect yourself from sudden tactical blasts and to reduce the calculation (believe me, in blitz, time flies and before you know it, you are in the time trouble ), but keep enough peaces on board so you can complicate if you feel you can win ( exchanging 2 minor pieces would suffice since it greatly simplifies, but still leaves you with good chances to complicate if you really need a win).

BE VERY CAREFUL WHEN EXCHANGING PIECES!!!

In blitz, people often offer exchanges to simplify, so always assess the resulting position that will arise after the exchange.

This method will give you the best results-offer them unfavorable exchange ( e.g. offer your bad bishop for their good one ). You will be surprised how many people make wrong exchanges!

Practice tactical blows on the real games, NOT on the artificial studies/problems and try to find those examples related to the openings you play.This will additionally protect you from sudden blows.

And again, prepare openings thoroughly! ( I just can't emphasize this enough ). You will want to use your time only for calculation, not on the opening.

EDIT ( updated on December, 20th 2013 ):

About the clock:

Do not forget to press it when you play the move-most beginners/those who are not used to clock, forget it.

What will happen is this:

After you make the move, without activating the opponents clock, he/she will just stare at the board like an idiot, doing nothing.

You will start wondering what is going on-are you winning so he/she thinks how to save the game, or did you play something utterly stupid so your opponent calculates the refutation?

Neither is happening! Your opponent saw you not pressing the clock, so patiently waits for your time to expire, in order to claim win due to you exceeding the time limit.

Yeah I know...there are all kind of people out there :)

As for notation, as soon as you play your move, press your clock first, and then write down the move.

Why? Because if you play blitz at more than 5 minutes each, you do not have to write down moves if you have less than 5 minutes ( double check this, since it was a long time I have played blitz, and this information was told to me by a friend ), and your time is always the highest priority in blitz, you can always write down the move after the game.

If I recall correctly, in 5 minute blitz you do not have to write down moves ( again, double check this ).

Hopefully this will help you.

Good luck!

Best regards.


Nxd4 is not the best response to Bxd4, instead exd7 counter-attacking the Black Queen wins a piece:
[Result "*"]
[FEN "4q1k1/p4pb1/r4npp/4P3/n2B4/5NNP/5PP1/Q4RK1 b - - 0 1"]

1...Nd7 2.e6 Bxd4 3.exd7 Qxd7
    ( 3...Bxa1 4.dxe8=Q+ )
4.Nxd4 *

I think the term you are looking for is desperado, even though it doesn't seem quite a typical use to me. Quoting wikipedia (https://en.wikipedia.org/wiki/Desperado_(chess))

In chess, a desperado piece is a piece that is en prise or trapped,
but captures an enemy piece before it is itself captured. This can be
in either a situation where both sides have hanging pieces, "...in
which you use your doomed piece to eat as much material as possible
before it dies";[1] or alternatively a sacrifice that will result in
stalemate if it is captured.


Prove that White is not allowed to castle here

This is actually a rather typical retrograde problem, just start with the most basic observations:

We see that black is missing both rooks and the f8 bishop. Given black's pawn structure it's easy to see that neither the f8 bishop nor the a8 rook could have escaped the structure, thus they must have been captured on the 8th row (by a white knight for example). This leaves us with the h8 rook, for which there's only one plausible choice left, namely having been captured on the b4 square by the a3 pawn.

As for white, the only missing piece is the rook, which must evidently have been captured on the g5 square by the h6 pawn.

Now we arrive at the real question: which rook could have logically been captured first, the one on g5 or the one on b4? Surely if the black h8 rook is to be captured on b4, it must first have been freed by the white rook being in turn captured on g5, but that's impossible, as the h8 rook being taken off on b4 is the very thing that must have freed white's a1 rook in the first place! Which leaves us with one remaining logical possibility: White's h1 rook must have been the one coming out and subsequently captured on g5, which then in turn frees black's h8 rook, to come out and be taken off on b4 by white, which finally freed the a1 rook.

Thus the rook you see currently on h1 is actually the rook coming all
the way from a1 (once freed), with the original h1 rook having been
lost on g5. Given this sequence as the only possible logical sequence
leading up to the current position, white cannot castle, as for
castling to be allowed, neither the king nor the rook must have
moved.

These kinds of puzzles usually go under the category of retrograde analysis, where unlike usual chess puzzles where the intent is to find the best moves/tactics or mates, in retrograde problems it's rather often just a logical question that can be answered by considering the basic rules of the game, and trying to find the only logical sequences (not move by move though, just the necessary ideas) that could have led to the position given in the puzzle. So if you're not familiar with these kinds of problems you may indeed find it difficult to attack them at first. Retrograde problems in chess are really fun to solve, specially as soon as you get the handle of them and start solving the real difficult ones. The solving process is really similar to that of a detective solving a crime, since if you think about it, you're given some clues and trying to figure out what could and could not have happened ;)

Addendum after some comments:
(This is regarding which of the black rooks may have been taken off on b4, although this fact leaves the proof unperturbed.) The a8 rook is trapped on the 8th row, as the only possible way for it to escape the 8th row would be via the h-file, which once opened (i.e white losing the h1 rook on g5) would first let the original h8 rook out. Of course you can always assume the h8 rook and f8 bishop were for example first taken off by a knight, then the a8 rook was the one coming out to get captured on b4 (e.g. Nc6, Qe6, Kd7 to open the 8th row), but for the purpose of the puzzle it won't matter, as in either scenario white wouldn't be able to castle as the same arguments hold.


Ivanchuk has played several games in the Scandinavian variation of the Alekhine. You can find the games for example here, if you sort by black Elo.


Mate In N algorithm-Lichess Computer Analysis

It is possible, if the computer program has a bug... A position is assigned a win-in-(k+1) only when one move from that leads to a loss-in-k, and assigned a loss-in-k only when every move from that leads to a win-in-k or when k=0 and it is a checkmate. So every correct chess program will never assign a position to win-in-12 and then later revise it to win-in-15 due to "searching deeper". No heuristic pruning techniques should ever affect this, as heuristic pruning can only weaken the evaluation away from a win/loss (in a correct program).
However, it is possible that the program is designed to search deeper if the input position satisfies a certain criterion C, in which case it may find a win-in-12 for a given position X that satisfies C, but then one move later the resulting position Y no longer satisfies C and so the program does not search as deep lines as it did for X, and so fails to find a win-in-11 for Y! It may still be able to prove a win-in-15 for Y if it has some rudimentary endgame evaluation. For example, KQK is always a win-in-10, so we do not have to do any search to return win-in-10 in such a position. Thus the program might do a more shallow search for Y and see a KQK in the search tree and immediately return win-in-10, but a deeper search would have revealed that it was actually win-in-5. This can produce the observed effect, but is due to "searching less deep"!
Note that clicking on "go deeper" on Lichess analysis may not use the same memoization table that had been used before at the lower depth level. One clear example is here where the cached analysis states #−30 but if you click "go deeper" it clearly starts completely from scratch. This is expected; after all it makes no sense to store huge tables along with the cached analysis. I think that if you cannot provide an actual concrete example of the behaviour you are asking about, it is difficult to address your hypothetical question more than I already have.


Why does Lichess mark this move as "?!"?

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

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

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

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

 1. Kc2 (1.Kc4)


Yes, there is. The FairyMax engine is quite flexible, it changes how it plays chess from a configuration text file. Please take a look at the official version:

http://home.hccnet.nl/h.g.muller/fmax.ini

Do you see Capablanca chess, where the board is bigger? Do you see all those variants?

Some links:

http://www.open-aurec.com/wbforum/viewtopic.php?f=19&t=53353
http://www.open-aurec.com/wbforum/viewtopic.php?f=2&t=53826

You'll need to learn how to use the file. Please ask on the Winboard forum for any further assistance (I don't think there is proper documentation, you just need to ask). Pay close attention to H.G.Muller, he is the man who did all of that.

Stockfish doesn't allow easy transition to a variant. It's still possible but you'll need to battle at the source code level. Not simple. Nothing will change unless you rewrite Stockfish from scratch. Use Winboard/Fairymax, not Stockfish. Winboard/Fairymax is the best variant engine available.


Machine Learning parameters for human vs computer detection

Coming from a machine learning background, although this sounds like a supervised learning task, do not expect any decent results.
Most players today use the computer to analyze positions and prepare quite deep with the engines. So the distinction there is lost in most medium to high level game play.
Also, simply knowing whether a game was played by a computer or not is not sufficient. To train any model, you need to have an intuitive understanding of your data. In this case, simply the sequence of moves played is not sufficient.
But if you're still bent on trying your hand at this, you could look into sequence classification using LSTM networks using an encoded matrix as inputs, but I don't see it working very well at all. If a human can't tell the difference, any model you develop won't be able to either.


The difficulty of finding the winning idea in this knight versus bishop endgame

Note: This is an analysis of the position at move 34. Obviously, White's play in the beginning of the endgame was poor and he should never have entered such trouble.

Black's advantage is clear and long-lived because he has the better minor piece, a knight vs a bad bishop with a locked center. Whether this advantage is enough for a win requires analysis, of course.

Black has a great stronghold on e4, and your reflex to place the knight there seems very natural, but... this is rather the right plan in the middlegame, not in the endgame !

In a minor piece endgame, the best piece to place on a central stronghold is not the knight anymore (as in the middlegame, or in most multi-pieces endgames with rooks), but the king ! As long as it remains safe, the king on the stronghold is centralized, attacks the pawns around it, and often threatens to invade the enemy camp.

This principle is very often applied in isolani endgames. Imagine Black has an isolated pawn on d5. If we still have rooks, White will gladly place his knight on d4, blocking the pawn and controling a bunch of important squares, and try to generate play down the c-file. But what happens if rooks are exchanged and Black has no control of d4 ? The winning plan usually becomes Nd4-e2, Kd3-d4, Ne2-c3, and Pd5 will soon fall. The king, not the knight, makes the decisive threats from d4.

This applies to your game. Just place the bK on e4 and you will see that White is doomed to passive defense of Pe3 and of the entry squares d3 and f3. That's why the right plan on move 34 is to try and gain access to e4 for your king.

34...Kf5 threatens 35...g4+ followed by ...Ke4, so 35.h3 seems forced. However, you then make use of your doubled g-pawn to open the way with 35...g4+ 36.hg4 Ng4 and there are three plans to expel the wK from f3:

bring your second g-pawn to g4. Then you can reach a position with Ke4, Pg4, Nf5 vs Ke2, Bf2 that is actually a zugzwang with White to play. How to give him the tempo, however, is not obvious. Most probably you will have to go for e6-e5, dxe5, Kxe5, Kd3, and try to gain access to the fourth rank again. Some winning chances, but my feeling is that White will hold if there is no refinement before ; I will stop the analysis here for now.

With an animated diagram:

[Title "jasonhaller-RewanDemontay"]
[FEN "6k1/1pn3p1/p1p1p1p1/2Pp4/PP1P4/4P3/1B4PP/5K2"]
[startply "67"]

1. d4 d5 2. Nf3 Nc6 3. c4 e6 4. Nc3 Bb4 5. Qc2 Nf6 6. e3 O-O 7. a3 Bxc3+ 8. Qxc3 Bd7 9. Bd3 Qe7 10. c5 a6 11. b4 Na7 12. O-O Bb5 13. Re1 Bxd3 14. Qxd3 c6 15. Nd2 Nb5 16. a4 Nc7 17. Bb2 Rfe8 18. Nf3 Rab8 19. Ne5 Nd7 20. f4 Nxe5 21. fxe5 f5 22. exf6 Qxf6 23. Rf1 Qg6 24. Qxg6 hxg6 25. Rae1 Rf8 26. Rxf8+ Rxf8 27. Rf1 Rxf1+ 28. Kxf1 Kf7 29. Kf2 Kf6 30. Kf3 Ne8 31. Kf4 g5+ 32. Kg4 Kg6 33. g3 Nf6+ 34. Kf3 Kf5 35.h3 g4+ 36.hxg4+ Nxg4 37.Bc1 Nf6 38.Bd2 g5 39.Bc3 g4+ 40.Ke2 Ke4 41.Be1 Ng8 42.Bf2 Ne7 43.Bg1 Nf5 44.Bf2 e5 45.dxe5 Kxe5 46.Kd3

try to check with the knight, keeping Pg7 on place. If you can get a similar position with Ke4, Nf5, you are certainly winning because you have spared yourself tempo-moves with the Pg7. It means that White has to prevent such plan by playing g4 himself when his king still stand on f3, but then the Pg4 himself will become a weakness.

If White waits passively:

[Title "jasonhaller-RewanDemontay"]
[FEN "6k1/1pn3p1/p1p1p1p1/2Pp4/PP1P4/4P3/1B4PP/5K2"]
[startply "67"]

1. d4 d5 2. Nf3 Nc6 3. c4 e6 4. Nc3 Bb4 5. Qc2 Nf6 6. e3 O-O 7. a3 Bxc3+ 8. Qxc3 Bd7 9. Bd3 Qe7 10. c5 a6 11. b4 Na7 12. O-O Bb5 13. Re1 Bxd3 14. Qxd3 c6 15. Nd2 Nb5 16. a4 Nc7 17. Bb2 Rfe8 18. Nf3 Rab8 19. Ne5 Nd7 20. f4 Nxe5 21. fxe5 f5 22. exf6 Qxf6 23. Rf1 Qg6 24. Qxg6 hxg6 25. Rae1 Rf8 26. Rxf8+ Rxf8 27. Rf1 Rxf1+ 28. Kxf1 Kf7 29. Kf2 Kf6 30. Kf3 Ne8 31. Kf4 g5+ 32. Kg4 Kg6 33. g3 Nf6+ 34. Kf3 Kf5 35.h3 g4+ 36.hxg4+ Nxg4 37.Bc1 Nf6 38.Bd2 Nh7 39.Bc3 Ng5+ 40.Ke2 Ke4 41.Be1 Nf7 42.Bf2 Nh6 43.Bg1 Nf5 44.Bf2 g6 45.a5 g5 46.g4 Nh6

then Black wins a pawn and the game.

But if White reacts with g4:

[Title "jasonhaller-RewanDemontay"]
[FEN "6k1/1pn3p1/p1p1p1p1/2Pp4/PP1P4/4P3/1B4PP/5K2"]
[startply "67"]

1. d4 d5 2. Nf3 Nc6 3. c4 e6 4. Nc3 Bb4 5. Qc2 Nf6 6. e3 O-O 7. a3 Bxc3+ 8. Qxc3 Bd7 9. Bd3 Qe7 10. c5 a6 11. b4 Na7 12. O-O Bb5 13. Re1 Bxd3 14. Qxd3 c6 15. Nd2 Nb5 16. a4 Nc7 17. Bb2 Rfe8 18. Nf3 Rab8 19. Ne5 Nd7 20. f4 Nxe5 21. fxe5 f5 22. exf6 Qxf6 23. Rf1 Qg6 24. Qxg6 hxg6 25. Rae1 Rf8 26. Rxf8+ Rxf8 27. Rf1 Rxf1+ 28. Kxf1 Kf7 29. Kf2 Kf6 30. Kf3 Ne8 31. Kf4 g5+ 32. Kg4 Kg6 33. g3 Nf6+ 34. Kf3 Kf5 35.h3 g4+ 36.hxg4+ Nxg4 37.Bc1 Nh6 38.Bd2 Nf7 39.g4+ Kg5 40.Kg3 e5 41. dxe5 Nxe5 42.e4+ Kf6 43.exd5 cxd5 44. b5

White has some counterplay and should draw.

So the most dangerous plan is probably to gain even more space with e6-e5-e4, place the king on g4, and target Pg3.

It looks promising:

[Title "jasonhaller-RewanDemontay"]
[FEN "6k1/1pn3p1/p1p1p1p1/2Pp4/PP1P4/4P3/1B4PP/5K2"]
[startply "67"]

1. d4 d5 2. Nf3 Nc6 3. c4 e6 4. Nc3 Bb4 5. Qc2 Nf6 6. e3 O-O 7. a3 Bxc3+ 8. Qxc3 Bd7 9. Bd3 Qe7 10. c5 a6 11. b4 Na7 12. O-O Bb5 13. Re1 Bxd3 14. Qxd3 c6 15. Nd2 Nb5 16. a4 Nc7 17. Bb2 Rfe8 18. Nf3 Rab8 19. Ne5 Nd7 20. f4 Nxe5 21. fxe5 f5 22. exf6 Qxf6 23. Rf1 Qg6 24. Qxg6 hxg6 25. Rae1 Rf8 26. Rxf8+ Rxf8 27. Rf1 Rxf1+ 28. Kxf1 Kf7 29. Kf2 Kf6 30. Kf3 Ne8 31. Kf4 g5+ 32. Kg4 Kg6 33. g3 Nf6+ 34. Kf3 Kf5 35.h3 g4+ 36.hxg4+ Nxg4 37.Bc1 e5 38. Bd2 {38. dxe5 Nxe5+} e4+ 39.Kg2 Nh6 40.Kh3 {40.Be1 Kg4 41. Bf2 Nf5} Nf7 41. Bc3 Ng5+ 42.Kh4 Nf3+ 43.Kh3 Kg5 {Ng1}

Black's winning chances are very serious. This third plan would be my favorite choice.

Computer analysis will refine this and probably prove me wrong more than once, but it also spoils all the fun of searching for the truth...


Is there an engine that finds the best "practical" move?

You're describing something that's very similar to contempt. The idea with contempt is that if you keep more dynamism in the position, a weaker opponent is more likely to make mistakes that you can then exploit. Therefore, given two moves that yield similar evals, an engine with high contempt score will choose the one that keeps more dynamism in the position. The current-strongest traditional engines all have contempt implemented (example for Komodo).

The danger of contempt is, against a strong opponent, high contempt can get you killed - you are after all forcing the engine to play a weaker move just to keep the game alive.