text:
Can it be proven that 11. 0-0-0+ is legal in this position?
Because the chess site this was on takes its puzzles from real games and gives the move numbers, potential solvers knew that the following position was reached after exactly 10 moves by each player.
[fen "2bk2nr/p1p2ppp/2p5/2p5/2P1P3/2N5/Pr3PPP/R3KB1R w - - 0 11"]

Given that information, can one prove that 11. 0-0-0+ in the above diagram is legal?

(i.e., that neither the white King nor the Ra1 has moved so far)

It seems to me like that's not enough total moves for white to have spent two

moves "shuffling", but I can't come up with any proof or a counterexample-game.

This might be more appropriate on puzzles.SE, but when I searched this site I saw lots of retrograde analysis problems.  That position is taken from this game.

So the mission, if one chooses to accept it, is to provide an example game that has the above position after exactly 10 moves and 0-0-0 is still possible. Presumably it is white to move?

No. The "mission, if one chooses to accept it, is to" either "provide an example game that has the above position after exactly 10 moves and 0-0-0 is" not "still possible" or prove that white must still be allowed to castle.  (It is white to move.)

@Phonon: No. Since your definition of "redundant moves" is global rather than local, it's not quite clear that your example game does not actually have any redundant moves.

This game is a real game. THe last moves are 9. NxB(c5) dxc5 10. QxQ+(d8) KxQ 11. o-o-o+

The idea of 0-0-0+ reminds me of the game Feuer - O'Kelly de Galway: http://www.chessgames.com/perl/chessgame?gid=1104131

Reasoning by hand about proof games is fine, but is more fun for positions which have been designed by humans to be solvable and to contain interesting features. Automatic verification is standard for all but the most complex of compositions, and is normally done by specialized engine, of which there are several available for free online.
IMHO, the best proof game engine for OP's position is Natch. Running for 49.03 seconds, it found 2493 "solutions" for how to reach the position in exactly 10.0 moves. None of them contained the strings e1, a1 (or 0-0-0!) and so there is no way that White could have lost castling rights in the prior play.
Notes:
(1) The way that Natch reports consolidates results to reduce the length of the report, so there are rather more than 2493 actual proof games, but that doesn't affect the conclusion.
(2) What about other engines? Popeye is not the most performant for this kind of position, and Euclide would have terminated as soon as it found that there wasn't a unique solution. But both are excellent engines.

Ok after playing around with a couple of lines, I finally found one line that shows it's still perfectly legal to play long castles for white at move 11, here it is:
[Title "possible 11.O-O-O+"]
[StartFlipped "0"]
[fen "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1.e4 e5 2.Nf3 Nc6 3.c4 Rb8 4.d4 exd4 5.Nxd4 Bc5 6.Nxc6 dxc6 (6... bxc6 7.Be3 d6 8.Bxc5 dxc5 9.Qxd8+ Kxd8 10.Nc3 Rxb2 11.O-O-O+) 7.Qxd8+ Kxd8 8.Be3 b6 9.Bxc5 bxc5 10.Nc3 Rxb2 11.O-O-O+

Added another continuation, taking on c6 with the b-pawn, same position results and same number of moves needed!
To conclude, because I reached the given position in exactly 11 moves, and did not play any redundant moves (e.g. Nf3 then back to Ng1 again), it means that all the played moves were necessary, their order can be different, but point is there was no spare move to use and destroy white's castling (e.g. an impossible scenario would be black exchanging queen on d1, Kxd1, then black plays Kxd8, and white goes back to e1, but that took up 2 more moves than the line I showed, so impossible to reach the position you're looking for in 11 moves after such line)
Long story short, castling is perfectly possible here, and in 11 moves black could not have done anything to prevent us from castling and still manage to reach the final position we want. Interesting post by the way, +1.
Alternatively one can also just look at the final position and count the necessary number of moves, that must take place for this position, I elaborate: have the final position in mind: let's take black's point of view: Pawn moves needed to obtain the final position:

e5
exd4 (why black has to take on d4 and not white on e5 is explained in the diagramm below)
bxc6 or dxc6
b6 or d6
bxc5 or dxc5,

Development moves:

Nc6 (to be captured on c6, otherwise there cannot be a pawn on c6 and not have knight on b8)
Bc5 (otherwise c5 pawn impossible)
Rb8 (otherwise Rxb2 never possible)

Remaining necessary moves: Queen d8 capture and pawn b2 capture:

Kxd8
Rxb2

And we find ourselves at the 11th move again, where all we did was just consider the most straighforward ways our pieces could end up where they are in the shown puzzle.
Let's see if we reach the same position via another path, showing why exd4 is the fastest way to reach the final position:
[Title "Why black must take on d4 and not white on e5:"]
[StartFlipped "0"]
[fen "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1.e4 e5 2.Nf3 Nc6 3.c4 Rb8 4.d4 Bc5 5.dxe5 Nxe5 6.Nxe5 d6 7.Nc6 bxc6 8.Be3 Rxb2 9.Bxc5 dxc5 10.Qxd8+ Kxd8 11.Nc3

Here we are at move 11 and we still have to play Nc3... clearly because we played 2 knight moves for black.
Finally let's demonstrate why in the fastest path to the final position, white has to be taking on d8 (queen exchange) and not the other way around:
[Title "A line white cannot castle but the final position cannot be reached within the 10 required moves (so impossible for our purposes)"]
[StartFlipped "0"]
[fen "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1.e4 e5 2.Nf3 Nc6 3.c4 Rb8 4.d4 exd4 5.Nxd4 Bc5 6.Nxc6 dxc6 7.Nc3 Qxd1+ 8.Kxd1 b6 9.Be3 Kd8 10.Bxc5 bxc5 11.Ke1 Rxb2

We lost 2 king moves(capture on d1 then back to e1) for white in this line, hence the Rxb2 only happening at the 11th move.
So it was shown that the only line leading up the the final position within 10 moves, is one where white still must be able to castle.
EDIT: A summary of the discussed elements in the comments:
The proof presented in this answer is purely deduction based, in the sense that the simple fact of having reached the position in exactly 11 moves without having made any redundant (or insensitive to the position) moves, implies that 11.O-O-O+ should be legal without exception.
What does redundant mean here? "Redundant moves": here, are defined as moves that do not bring us any closer to the final position, or would even deviate us from it. For example playing Nf3, then back to Ng1, would be redundant. Playing Be2 then back to Bf1 would be redundant, and so on.
Point being, in any variation, you may come up with, that would take away white's castling rights, will imperatively entail redundant moves, that will in turn delay reaching the final position by a couple of moves. (As an exercise, try some of your ideas, it is interesting, and see how many moves it takes you.)
Looking at such problem from a combinatorics point of view, may be possible, but would be too complicated as we're looking at a depth of moves(tree lines) resulting from 11 moves. Instead, like most chess puzzles, one has to look at it from a purely heuristic point of view, and find the right ideas that would go in the direction of proving the question at hand. Finally, in chess, one usually has an easier time looking for counter examples(proof by contradiction), which is why it is encouraged to look into some of the lines on your own.

That it was possible to reach the position in 11 moves was obvious from the question, that was given. What's asked is proof that it can't be done any faster.

I added some more details just now.

Unfortunately, this answer just considers "the most straighforward ways our pieces could end up where they are in the shown puzzle", rather than all possible ways, so it doesn't give a proof.

It is a proof by deduction, in the sense that the simple fact of having reached the position in exactly 11 moves without having made any redundant (or insensitive to the position) moves, implies that 11.O-O-O+ should be legal without exception, as elaborated in the answer. Furthermore, had the puzzle asked for 12.O-O-O+, then your doubt about whether it is legal or not would be perfectly valid. Try to mull over this redundancy idea, and shortest path to the position, and I'm sure that you will see why these are sufficient elements for such proof.

Finally, the other examples (lines) in my post, have the purpose to showcase the fact that other variations that destroy the castling rights of white, will always exceed the 11 move limit if they are to reach/lead to the position given by the puzzle. As any move wasted to move the white king, or the queen side rook, will suffice in exceeding the limit, because such moves in this exact position do not contribute to reaching the final setup.

We are not given that the position was reach "without having made any redundant (or insensitive to the position) moves".  How do you show that black must have played e5?  How do you show that black must have played b6 or d6? (as opposed to taking on c6 twice and playing c5 in-between) How do you show that black's queen-knight must have been captured on c6? (as opposed to moving to a6 or d7; I believe that based on this answer I can prove it wasn't captured on d8) How do you show that "otherwise c5 pawn impossible"?  How do you show that black's queen must have made a capture?

All those scenarios are possible, to reach the final position, but they will exceed the 11 move limit, hence not of interest. Please read my answers carefully...Try a couple of these lines you have in mind, you will see for yourself, as I did, before answering.

You might be thinking that your idea of "redundant moves" works for the proof.  In order to get that, you would need to first define that term, rather than just give an example of it.    I'll read your answers carefully when I get back in a few hours, but so far I haven't seen any showing that the possibilities I mentioned would exceed the move limit.

I have defined what I mean by "redundant moves": here, they're defined as moves that do not bring us any closer to the final position, or would even deviate us from it. For example playing Nf3, then back to Ng1, would be redundant. Playing Be2 then back to Bf1 would be redundant, and so on. It is imperative that you try out the ideas (lines) you have in order to reach the final position, and observe my claims on your own. It would be pointless to put 10 diagrams in a post, when the point can be made with 1-2.

Looking at such problem from a combinatorics point of view, may be possible, but would be too complicated as we're looking at a depth of moves(tree lines) resulting from 11 moves. Instead, like most chess puzzles, one has to look at it from a purely heuristic point of view, and find the right ideas that would go in the direction of proving the question at hand. Finally, in chess, one usually has an easier time looking for counter examples(proof by contradiction), which is why I encourage you look into some of the lines on your own. It would be my pleasure to further discuss it with you.

A mathematician, a physicist, and an engineer are riding a train through Scotland. The engineer looks out the window, sees a brown sheep, and exclaims, “Hey! The sheep in Scotland are brown!” The physicist looks out the window and corrects the engineer, “Strictly speaking, all we know is that there is at least one brown sheep in Scotland.” ... (cont'd)

(cont'd) ... The mathematician looks out the window and corrects the physicist, “Strictly speaking, all we know is that at least one side of one sheep in Scotland is brown.” -- Source

As a physicist, I consider this sufficient proof ;) +1

We can deduce nine moves that white absolutely had to make to get to this position.

At least three moves were required to put white's pawns and its queen's knight there (3 total)
Either the c- or d-rank pawn was captured after it moved. That's another move (4 total)
The pieces captured on c5 and c6, whatever they were, needed at least two moves to get there. That's four extra moves. (8 total)
If the piece captured in c6 isn't white's missing knight (which needs 3 move to get there), that knight had to be captured in d4 by the e pawn, and that means the queen or bishop had to capture it on their way to capture on the c-file, adding another move anyway (not to mention what it means about the missing white pawn). That's another move. (9 total)

This position without possible castling requires two more moves (moving the castle or king back and forth), and it's impossible to fit them in.

Aren't you assuming that the Black king captured a piece? Technically it's possible for the b and d pawns to be captured even if they don't move.

Dear Circeus, you are just repeating the elements of the list I had posted in my answer. Please try to add something original to your argumentation, that I had not already covered. Thanks, and please by no means should you take this as offensive.

@Phonon My solution is not the same. Yours looks at black moves and deduces "there was no spare move to use and destroy white's castling". My solution deduces white does not have the spare moves to move its castle or king back and forth.

@Wes I had realized that and was fixing my solution while you were commenting.

Yes but that's the same point, turned upside down, I didn't add another list for white because it would been pretty much a list of similar elements, as neither sides can allow redundancies...which I also elaborated with an example (last diagram). Your post is a valid answer, but it does not bring new content I'm afraid, maybe I'm wrong.

I don't understand your second point. Couldn't the black queen have taken the white pawn on d2?

Sorry, no, White -cannot- castle queenside in this position.  Retrograde analysis has nothing to do with it.  The official rules of Chess explicitly state that, in castling (either side), neither the king -nor the moved rook- is allowed to pass over a threatened square.  The Black rook on b2 ruins it.

A rook is allowed to pass a threatened square. Please check the official FIDE rules.

Hey sorry about the downvotes. But if it makes you feel any better, even GMs forget the rules about castling


text:
Openings that keep the king in the center on purpose?
Discounting cheap tricks to mate in only a few moves. Are there any serious openings that keep the king in the center with no intention of castling?

There are many respectable opening lines where the king stays in the center. A popular opening at the highest level is the Berlin Defense:
[FEN ""]
1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. O-O Nxe4 5. d4 Nd6 6. Bxc6 dxc6 7. dxe5 Nf5 8. Qxd8+ Kxd8

There are some that have been played at the highest level.
Philidor Defense
   [Event "Grand Slam Final 5th"]
   [Date "2012.09.25"]
   [White "Vallejo Pons, Francisco"]
   [Black "Carlsen, Magnus"]
   [Result "0-1"]
   [WhiteElo "2697"]
   [BlackElo "2843"]
   [FEN ""]

   1. e4 d6 2. d4 Nf6 3. Nc3 e5 4. dxe5 dxe5 5. Qxd8+ Kxd8 6. Nf3 Bd6 7. Bg5 Be6
   8. O-O-O Nbd7 9. Nb5 Ke7 10. Nxd6 cxd6 11. Bb5 Rhd8 12. Nd2 h6 13. Bh4 g5 14.
   Bg3 a6 15. Bxd7 Rxd7 16. f3 Rc8 17. Kb1 Nh5 18. Nf1 f5 19. exf5 Bxf5 20. Ne3
   Bg6 21. Rd2 Ke6 22. b3 b5 23. Kb2 d5 24. Re1 Nxg3 25. hxg3 h5 26. c3 d4 27.
   cxd4 Rxd4 28. Rxd4 exd4 29. Nc2+ Kd5 30. Nb4+ Kd6 31. Rc1 Rxc1 32. Kxc1 h4 33.
   gxh4 gxh4 34. Nxa6 Bd3 35. Nb4 Bf1 36. Kd2 Bxg2 37. Ke2 Bh3 38. a4 Bf5 39. axb5
   d3+ 40. Ke3 h3 41. Nxd3 Bxd3 0-1

Old Indian Defense
    [Event "Gibraltar Masters 11th"]
    [Date "2013.01.23"]
    [White "Jameson, David"]
    [Black "Ivanchuk, Vassily"]
    [Result "0-1"]
    [WhiteElo "2143"]
    [BlackElo "2758"]
    [FEN ""]

    1. d4 Nf6 2. c4 d6 3. Nc3 e5 4. dxe5 dxe5 5. Qxd8+ Kxd8 6. Bg5 c6 7. Nf3 Nbd7
    8. Ne4 Kc7 9. Nxf6 gxf6 10. Bh4 Bb4+ 11. Nd2 f5 12. O-O-O a5 13. Nf3 a4 14. a3
    Bd6 15. Ng5 Rf8 16. e4 Nc5 17. f3 Ra6 18. Nxh7 Rh8 19. Nf6 Rb6 20. Bf2 Be7 21.
    Kc2 Rb3 22. Bxc5 Bxc5 23. exf5 Bxf5+ 24. Bd3 Be6 25. Ne4 Bd4 26. Rb1 f5 27. Nd2
    Rb6 28. b4 c5 29. h4 Rd6 30. Rh2 Rhd8 31. Rd1 cxb4 32. axb4 a3 33. Nb3 a2 34.
    Rhh1 a1=Q 35. Nxa1 Bxa1 36. h5 Bd4 37. h6 Ra6 38. Kb3 Rda8 39. Bb1 Ra3+ 40. Kc2
    Bxc4 41. h7 Bb3+ 42. Kd2 Bxd1 43. h8=Q Rxh8 44. Rxh8 Ba4 45. Bxf5 Ra2+ 46. Ke1
    Bf2+ 47. Kf1 Bb5+ 0-1

Sicilian Defense Taimanov Variation with 4 knights
   [Event "Rubinstein Memorial 35th"]
   [Date "1998.08.18"]
   [White "Shirov, Alexei"]
   [Black "Krasenkow, Michal"]
   [Result "1-0"]
   [WhiteElo "2720"]
   [BlackElo "2655"]
   [FEN ""]

    1. e4 c5 2. Nf3 Nc6 3. Nc3 e6 4. d4 cxd4 5. Nxd4 Nf6 6. Nxc6 bxc6 7. e5 Nd5 8.
    Ne4 Qc7 9. f4 Qb6 10. c4 Bb4+ 11. Ke2 f5 12. Nf2 Ba6 13. Kf3 Ne7 14. Be3 Bc5
    15. Bxc5 Qxc5 16. Qd6 Qb6 17. b3 c5 18. Be2 Rc8 19. Rhd1 Rc7 20. Ke3 Bb7 21.
    Bf3 Bxf3 22. gxf3 Qb7 23. Rg1 Rg8 24. h4 Nc6 25. Nd3 Nb4 26. Nxb4 cxb4 27. h5
    Qb6+ 28. Qd4 Kf7 29. Rg2 Qc6 30. Rd1 a5 31. Qd6 Qxd6 32. Rxd6 Ra8 33. Rd1 Rg8
    34. Kd4 Rc6 35. c5 Rc7 36. Rdg1 Rc6 37. Kc4 Rc7 38. Kb5 Ra7 39. Ka4 Raa8 40.
    Rd2 Ra7 41. Rd6 Rc8 42. Rc1 Ke7 43. Rb6 Kd8 44. Rc2 h6 45. Rb5 Kc7 46. Rg2 Rg8
    47. Rb6 Raa8 48. Kb5 Ra7 49. c6 g5 50. hxg6 dxc6+ 51. Rxc6+ Kd7 52. g7 a4 53.
    Rd2+ Ke7 54. Kb6 Rd7 55. Rxd7+ Kxd7 56. Rc7+ 1-0

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text:
Alternative plan in the Caro-Kann
I'm a Caro-Kann player who is coming up against the line 1. e4 c6 2. c4.
This line has a few names, such as the "Anti Caro-Kann" and the "Quasi Panov-Botvinnik".
The books recommend 2...d5. Afterall 1...c6 prepared 2...d5. But the line 2...d5 3. cxd5 cxd5 4. exd5 Qxd5 leads to a move down variation of the regular Panov-Botvinnik, so the books recommend after 4. exd5 to play 4...Nf6 to eventually regain the pawn.
My question is, can black feasibly side-step these tricky variations with 1. e4 c6 2. c4 b5(!?). Does this reach a playable middlegame for black?

This is a creative idea but unfortunately it does not look playable. After 7 minutes, Stockfish 5 gives the position after 2... b5 as +.87. This means that white is up a pawn for very little compensation.

Oh gosh... can't believe... asking engine for evaluation after 2nd move! 0.87, yay! And what about all those theoretical positions with even over 1.0? Like some of King's Indian? Seriously.

This is nothing like the King's Indian. You dropped a pawn.

And you need a chess engine here? After 2nd move?

Of course that b5 is complete nonsense but hey, it's not due to reason that "stockfish after 7 minutes says 0,87"!

What else do you propose? It's not like anyone's brain can match up to the evaluation power of a modern engine in an unknown position (unless it has a very specific set of characteristics, which this doesn't).

What else? To have a look at position and say: plain pawn down, opponent has a central pawn already which is going to be a lead in development. If something like this happens after 2nd move - no way b5 can be played. Using engine here is definitely wrong.

It seems to me that you could answer a question about 1. Nf3 f5 2. e4 the exact same way you just did and it would not be obviously wrong. The question asked if it would lead to a playable middlegame and an engine evaluation is a perfectly valid way to answer that. You could have written your own answer instead of commenting on mine with antagonistic sarcasm.

Not gonna comment that variation part. I am sorry if you're touched by my sarcastic comment. And if you think that analyzing such position with engine is cool thing, then I'm pretty curious what opening/defense you use. Is it some Nc3, Nf3, d4, Bf4 as white? Because that exactly is what engines are going to play if you turn off their opening books. There are positions for humans and for engines. After that 'b5' engine's help is redundant and unneeded, trust me

@user3447603, to reiterate part of Cleveland's previous comment, why not simply post your own contrasting answer along the lines you've suggested? That would be a most welcome addition to the thread.

Thanks @Cleveland. I think your computer analysis is a valid way to approach the question. I ran my own computer analysis, looked at some sample variations & discussed the position with friends. We concluded that the ...b5 idea is dubious. It's refuted by good play (black has no/little compensation). It was worthwhile looking into it because it challenges the automatic 2...d5

I noticed you posted you'd mostly found answer for yourself in the comments,  but...it reminded me of when I faced this while trying out the Caro-Kann.
It doesn't look like ...b5 works to me, either. If I were white I would play cxb5 and then let Black decide if and how to take back. There is no hurry to take on c6. The knight on b8 looks restricted, and a move such as ...a6 to force White to decide what to do with the b5 pawn wastes a move, and Black can't even get Benko-ish pressure on the a/b files unless ...c5 is played (which also gives up a move,) since White can just take back with bxc6. If black plays ...Qb6, then Nc3 (or even a4) defends the b5-pawn enough.
So from what I see Black doesn't get enough development for the pawn, and White has a pretty easy game with Nc3, d4, Nf3, etc.
When I played Black I found another pawn sac worked rather well: 4 ... Nf6 and while White can play Bb5+, Black can get it back. ...Bd7 5. Bc4 Qf7 6. Na3 Nxd5 as 7. Bxd5 Qe5 gets the bishop. This seems like a straightforward and low-risk way to equality.

b5 looks HORRIBLE. If there were not a pawn on c6, you could play a6, like in the Benko, but here, a6 would be answered by bc with a winning position.
It really does just drop a pawn for nothing as you gain no development advantage, or positional trumps.

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text:
Examples of recent early opening novelties at the top level
The world elite usually practises extremely deep opening preparation based on established theory, with the first move that has never been played before often coming after the 20th turn.
What are some recent (last 20 years) examples of top-class players deviating from theory early (say, on the 8th move or before)?

Aronian vs Anand at Candidates 2014 (http://www.chessgames.com/perl/chessgame?gid=1751406) was out of theory after Black's 3rd move, but only because White played an extremely odd opening which will probably never be repeated at the top level.
Aronian vs Leko at Morelia-Linares 2008 (http://www.chessgames.com/perl/chessgame?gid=1486033) featured a strong novelty on White's 9th move.

The problem with links is that they may break ... also they require an extra click to view.

The most bold novelty I have seen in recent chess is definitely the one played by Richard Rapport against Leinier Dominguez Perez on the 2014 Tata Steel tournament. You can find the game here. As a peek of the game, the first moves were:
[FEN ""]
[White "Richard Rapport"]
[Black "Leinier Dominguez Perez"]

1. c4 c5 2. Nc3 g6 3. g4!!

I find that Richard Rapport is a player that will most likely shock your chess, no matter what level do you have. He plays unconventional and uncompromising chess, trying new things against the best players. Even in this tournament, one of the best of the year, he played innovative chess in many of his games.
For a compilation of all his games in said tournament, click here.

Nice example! 1.c4 c5 2.Nc3 g6 3.g4 seems interesting. But it is not a novel idea to sacrifice the b-pawn or g-pawn for gaining a rapid bishop fiancetto in return. For example 1.b4 or 1.d4 d5 2.g4. Another thought on this variation is that black should perhaps start with 2...Nc6 and wait for white to move the g-pawn first!

Rapport mentioned that the whole idea was not to sacrifice it but as in the closed Sicilian one may play a KIA setup and eventually play g4, this "saves a tempo". Funny and original, but with drawbacks.

Another famous example is Zvjaginsev in the Russian Championship Superfinal 2005, against ex-FIDE World Champion Khalifman:
[FEN ""]
[Event "ch-RUS Superfinal"]
[Site "Moscow RUS"]
[Date "2005.12.20"]
[EventDate "2005.12.19"]
[Round "2"]
[Result "1-0"]
[White "Vadim Zvjaginsev"]
[Black "Alexander Khalifman"]
[ECO "B20"]
[WhiteElo "2659"]
[BlackElo "2653"]
[PlyCount "73"]

1. e4 c5 2. Na3 Nc6 3. Bb5 Qc7 4. Nf3 g6 5. c3 a6 6. Bxc6 Qxc6
7. O-O Bg7 8. d4 d6 9. d5 Qc7 10. h3 Nf6 11. Bf4 O-O 12. Re1
b5 13. Qd2 Bb7 14. Rad1 Rfe8 15. c4 Qb6 16. Bh6 Bh8 17. b3 e6
18. Ng5 exd5 19. cxd5 Re7 20. Re3 Rae8 21. Rde1 a5 22. Nb1 b4
23. Qc2 Nd7 24. Nd2 Ba6 25. Ngf3 Ne5 26. Bg5 Nxf3+ 27. Nxf3
Rd7 28. e5 dxe5 29. Nxe5 Rxd5 30. Nxf7 Rxe3 31. Rxe3 Kxf7
32. Re7+ Kf8 33. Qe4 Rd1+ 34. Kh2 Qd6+ 35. f4 Bf6 36. Bh6+ Kg8
37. Qa8+ 1-0

After 2.Na3!? Khalifman allegedly pointed at the knight and laughed out loud, but he still lost in the end. Zvjaginsev repeated the move quite a few times afterwards and other GMs have played it.
In general, novelties after move 20 are quite rare. Yes some opening theory goes that deep, and sometimes those lines are played, but especially the absolute top GMs tend to avoid such lines because the earlier both players are thinking on their own, the higher the chance the better player wins. Between move 10 and 15 is probably about normal.

I like 1.e4 c5 2.Na3, although I never play it myself. It actually makes sense: the knight is protected from the black Bf8, since the black c5-pawn is blocking the diagonal. It allows white to play c2-c3 and opens the c2-square for Na3-c2-e3. The knight can also do Na3-c4 followed by a2-a4 or Nc4-e3 controlling the center nicely!


text:
Anand - Carlsen Game 1 WCh 2014, why not 12.Qc3+?
In game 1 of the World Championship 2014 between Carlsen and Anand, Anand chose 12.gxf3. Why not play 12.Qc3+ instead? It takes control over the a1-h8 diagonal and prevents the black Nc6 to jump to d4 or e5. In addition, it gives white the option to grab on f3 with the queen, keeping the pawn structure on the kingside intact.
[FEN ""]
[Event "WCh 2014"]
[Site "Sochi RUS"]
[Date "2014.11.08"]
[Round "1"]
[White "Anand, Viswanathan"]
[Black "Carlsen, Magnus"]
[Result "1/2-1/2"]
[Eventdate "2014.11.08"]

1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.cxd5 Nxd5 5.Bd2 Bg7 6.e4 Nxc3 7.Bxc3 O-O 8.Qd2 Nc6 9.Nf3 Bg4 10.d5 Bxf3 11.Bxg7 Kxg7 12.Qc3+

I assumed it was because of 12...Ne5. That forces 13.Qxe5+ f6 14.Qsomewhere, after which the bishop can retreat, and Anand probably wanted the bishop over the knight. But I'm not sure enough of this to make it an answer.

@RemcoGerlich the answer is positional (involving some tactics).

doubled pawns are not as bad as you think

@David I think doubled pawns can cause serious problems and should be avoided when possible. It is a long term weakness and I prefer to avoid it. Having said that, every position should be judged individually. Still, in this example, gxf3 isolates the h2-pawn and creates weaknesses on f3 and f4 and I am not a big fan of that pawn structure.

@RemcoGerlich unfortunately that's not how the thinking process of a chess player works. As the answer has pointed out, there are concrete reasons why Qxf3 should be avoided. There is no way Black can attack the h2 pawn, which White can use as a "weapon" by playing h4-h5. There is also no clear way for Black to exploit the f3 and f4 weaknesses (...g5 is out of the question for now)

@David: As for your first sentence, I am a chess player and it is how my thinking process works, whereas the answer used an engine. Of course the chess content of your comment and the answer is better than my four moves...

@RemcoGerlich then you should definitely change how you think about evaluating chess positions. Concrete calculation should always prevail over abstract "principle".

@David while you have valid points, I think you can be more friendly in your comments. I think we are all exploring the game of chess and being friendly in our feedback is important to keep this community healthy and growing. Chess is not a tough and competitive quest for glory for everyone. For many people, I imagine it is a beautiful game that they enjoy. Dominating on the chess board is one thing, but dominating in the comment section is a different game in my view.

@David as for the evaluation of the position after gxf3, perhaps you can post a new question and it can be explored in the answer section of that question? I think this discussion is better suited for a new question, since my question focuses on Qc3+. I think doubled pawns is an interesting topic. It is always hard to interpret written text. Saying something like "definitely change" is more tough than "in my opinion" or "from my experience". English StackExchange next stop? Cheers.

           [FEN ""]
                [Event "WCh 2014"]
                [Site "Sochi RUS"]
                [Date "2014.11.08"]
                [Round "1"]
                [White "Anand, Viswanathan"]
                [Black "Carlsen, Magnus"]
                [Result "1/2-1/2"]
                [Eventdate "2014.11.08"]

                1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.cxd5 Nxd5 5.Bd2 Bg7 6.e4 Nxc3 7.Bxc3 O-O 8.Qd2 Nc6 9.Nf3 Bg4 10.d5 Bxf3 11.Bxg7 Kxg7 12.Qc3+ e5 (13.dxc6 Be4 14. Qe5 f6 15. Qc3 Re8 16. Be2 Bxc6)
    (13.gxf3 Nd4 )
   (13.Qxf3 Nd4 )
   (13.dxe6 Qf6 14. Qxf6 Kxf6 15. gxf3 fxe6)

Computer Houdini 1.5a w32 suggests 13... e5
Now four options for white 13.dc 13.de ep, 13.gf or 13.Qf3 anything else loses a piece.

After 13. dc black replies 13... Be4 and white cannot take pawn on e5. If 14. Qe5 then 14... f6 15. Qc3 (15 Qe4 loses a queen). 15... Re8 this forces white reply  16. Be2 and black just takes on c6 16.... Bc6 , this is a win for black.

13.gxf6 black moves its knight to the centre 13... Nd4 Knight on d4 cannot be moved. Pawn on f3 is weak. Black is better.

13.Qf3 Again same idea – black’s knight occupies the centre Nd4 and whatever white answer is black threatens to crush the white centre 14... c6. Again black is better (maybe not as good as after 13. gf)

13.dxe6 e.p. black needs to cover the diagonal – 13... Qf6 or 13... Qd4 anything else consolidates white’s position in the centre.
13...Qf6 14 Qf6 (otherwise black takes on c3) 14... Kf6 (forced) 15 gf (forced) 15... fe again black is better (weakness on f3)
13...Qd4 white cannot take on d4, so 14. e7 (if 14. gf black takes on c3 and again weakness on f3 is giving black an advantage)  14... Re8 15. gf again cannot take on d4. And now either 15...Re7 or 15... Qc3 and black has better pawn structure.

Good answer. I'd suggest upgrading from Houdini 1.5 to Stockfish 5 (https://stockfishchess.org/download/). Houdini 1.5 is the most advanced free version of Houdini but is quite old for a chess computer (released in 2010). Stockfish 5 is the latest version of Stockfish, a very small amount stronger than the most recent Houdini versions and is also free.

@Cleveland: Good point. Thank you for the link.


text:
Eating and drinking before and during a game
Food and liquid intake provides a human body with energy. Yet having a meal before a chess game can cause the body to focus more on digestion than chess. While lack of energy during a six hour game can cause loss of focus and thereby mistakes. Getting thirsty can have a similar adverse effect. When and what should one eat and drink before and during a chess game with classical time controls?

Related question: http://chess.stackexchange.com/q/1366/167 Though that one asks only about what to consume, and not about the timing of consumption, some of the answers there are pertinent to this question.

like the question!

Ideally a GM should answer this since only GMs usually play 6 hour games. But stackexchange isn't so lucky.

I already know the answer...besides the related question posted by ETD already has a lot of relevant information.

Even games with shorter time controls require focus and energy.

@RauanSagit, ya that is true.

It usually helps to keep orange juice with you during the game, just like Carlsen ;) I do it sometimes.

@Wes I've played many 6 hour games, and I'm only ~2000.

@JiK where? I'm 2150 but I never played a 6 hour game.

@Wes In Finland, there are some week-long tournaments with one game/day, allowing longer time controls than a normal weekend tournament with two games/day.

I have played tennis and chess both quite seriously for several years and my preparation towards a game when it comes to food, is basically the same. I try to eat around 4 hours before the game, some pasta with a light sauce or no sauce at all, avoid red meats 24 hours prior to the game and rink only water the day of the game. If I am to start in the morning then a light breakfast. In general I would rather play with a non-full stomach but here's the "secret", I do eat a chocolate bar at the beginning of my chess games and have a bottle of water at hand, this helps me greatly to keep my blood pressure normal, and able to focus on the game without feeling hungry even after 4 or 5 hours of play.
I guess my advice is to know what works for you, I have seen that avoiding heavy meals is generally good for performance but if you (like me) need an extra kick, pick up an energy bar of some sort (I would avoid coffee because of the possibility of needing to go to the toilet at a bad time).
All the best and hope it helps! :)


text:
Putting pressure on pawns
Why is it important to develop your pieces to put "pressure" on opponent's pawn(s)? I hear this a lot from YouTube videos in which experienced chess players commenting as the game develops. It's "just" a pawn! Why design a tactic or strategy around a pawn?

Attack is the best form of defense

Slightly related: http://chess.stackexchange.com/questions/2623

Attacking a piece is often not very useful: the piece does not feel any pressure but just moves away. A pawn won't escape so easily, so attacking a pawn forces the opponent's pieces to defend it and thus limits their freedom. There are a few possible gains of an attack on a pawn: the opponent cannot get enough pieces to defend the pawn so you immediately win the pawn, or his pieces are so badly placed defending the pawn that you can gain advantage on another part of the board, or the pawn has to move and leave weak squares on both sides of it because it cannot ever again protect the squares that it attacked a move ago.

Wow! Thank you so much for this great insight. Much appreciated.

In chess, pawns are the only pieces that cannot move backwards and the ones that have the less mobility. Thus, while in the opening a knight or bishop could simply retreat or be exchanged, a pawn usually has not so many options.
This is specially relevant in the opening. Consider for example the moves:
1.e4 e5 2.Bc4
In this position, black has may good moves: Nf6, Nc6 being the best, Be7, Bc5, Bb4 and d6 also being playable. Now, consider the moves:
1.e4 e5 2.Nf3
Now the e5 pawn is attacked and it black sees his options severely restricted if he wants to defend it, only Nc6 and d6 being sensible in order to do so.
Another important reason is that sometimes the pieces are unable to defend the pawn. This usually happens in the endgame or late middlegame, where some material has been exchanged, but also in some opening variations. To defend the pawn and not lose it, he has to be advanced, leaving behind him weak squares. Around those weak squares a player may be able later in the game to infiltrate the enemy territory and achieve a winning position.

Awesome! Thanks a lot. It feels wonderful to learn some deep insight about chess.

Yes, Be2 thank you @bof. I've corrected it.

Damn, yeah, Be7. Editing again. Thanks!

As a generality, you aren't going to win a good chess match with a singular, huge move that completely devastates your opponent. (If you do, they are not a worthwhile opponent and the playing level in question is novice.) Therefore, you need to coordinate attacks to be synchronized and cumulative. The more advanced the player, the more intricate and multi-faceted the attack. As your skill increases, you will start to use all of these minute details to your advantage, aspiring that they all add up to an insurmountable attack vector.
So, the more advanced you get, the more that these "tiny" things really matter.

First of all, the advantage of winning a pawn is usually enough to win the game (among good players). That's why they're worth attacking.
Second, pawns have the least mobility, that is the least ability to "run away." Their "tininess" also makes them the most vulnerable.
Third, because of one and two above, your opponent will (or at least should) make a major effort to defend pawns. In so doing, your opponent may create other (positional) advantages for you.


text:
Resources on the Bogo-Indian opening
I'm looking for good resources to learning the Bogo-Indian opening:
 [FEN ""]
 1. d4 Nf6 2. c4 e6 3. Nf3 Bb4+.

For background purposes, I play at around the 1750 elo level. I like closed positions (I play the Caro-Kann & Slav defence as Black, & always open with 1. d4 as White). Lastly, I'm motivated to learn the Bogo-Indian because I'd like to avoid the Nimzo-Indian.
Thanks in advance!

Just to confirm - it seems from your question that you want to play the Bogo from white's perspective. Is this correct?

Yes, that's right. I'd like to play the White side of this opening.

You probably want to take a look at a repertoire book for white with d4-c4-Nf3 - unfortunately I can't recommend any (I'm an Nc3 player myself - is the Nimzo really so bad? :)) sco-ish's suggestion of Avrukh seems like a good one.

There is a moderate chapter on it in Boris Avrukh's 1.d4 Volume 2, you can download a pdf excerpt from the website to see.
And the Sielecki book is at the time of writing (Nov 24 2014) not out yet (Jan 31 2015).
Other than that there aren't many decent works on this, and if so, most of them are outdated, scanning through databases and viewing GM games (preferably with annotations) can help a lot though.
There are also various videos on youtube, just search up the opening name
A Chessbase DVD by IM Andrew Martin covers it solely
Alternatively you can check the Chess Publishing Forum

One of my favorite chess you-tuber's - IM Christof Sielecki has written a book on it: Opening Repertoire: Nimzo and Bogo Indian http://www.amazon.com/dp/1781941092/
It would be worth to take a look at it!

The Complete Bogo-Indian Defense by International Master Maxim Chetverik is a pretty good resource. Here is the link.
https://www.newinchess.com/the-complete-bogo-indian-defense


text:
Is this continuation of D85, Gruenfeld Defence, Exchange Variation, tenable?
I am watching some commentary on the World Championship Games. This is from Game 1:
[FEN "rnbq1rk1/ppp1ppbp/6p1/8/3PP3/2B5/PP1Q1PPP/R3KBNR b KQ - 0 8"]
[White "Anand"]
[Black "Carlsen"]

The commentator states that Carlsen has several moves available to him at this point, including one which confuses me: 1. ...Bg4. I see that it stops White from castling, but after 2. f3 that Bishop seems silly. The pawn structure looks unfavorable but not fatally so after a bishop retreat. Alternatively, White can also play 2. Nf3, 2. Ne2 or 2. Be2 to set up an exchange.
What's the deal with 1. ...Bg4?

I'm not so sure about 2. f3. What about 2. h3, what has black achieved by provoking this move?

@DagOskarMadsen That's a good question. I guess it's a minor weakness if white castles kingside, but other than that I can't see much. I think we'd need a gruenfeld player to really say how the move fits in with black's common plans.

I have little idea about the Gruenfeld (hopefully someone who is more familiar or a better player than I am can give a more complete answer), but a few points you may have overlooked:

After 1...Bg4 2.f3, as you say the pawn structure is marginally weaker, but there's also a bigger problem of how white will develop the g1-knight. Nf3 is now impossible, Nh3 looks bad and if black's bishop stays on the c8-h3 diagonal he can then give white doubled h-pawns. Ne2 might look plausible,  but there's then a problem of how to move the knight from there. c3 and d4 can't be reached without a move vacating that square first, which will probably require other preparations as well, Nf4 too soon is dangerous as it could force white to make even more concessions in pawn structure if Bh6 is allowed, pinning the knight to the queen. Finally, g3 is a poor spot for the knight as the g6-pawn takes away two future squares and e4 is already being taken up by a pawn.
In grandmaster praxis, a draw with black is a respectable result, and trading off the bishops after 1...Bg4 2.Be2 gets black somewhat closer to this result.
1...Bg4 2.Nf3 gives white doubled pawns after the exchange, and the half-open file that results isn't that useful as it faces onto a reinforced pawn. It also leaves the knight on e2 (assuming white does not want to lose castling rights or lose the d4 pawn) with the same problems as mentioned above.

I think the purpose of Bg4 is to stop Nf3. Next, h2-h3 leads to a weakened pawn structure for white. While f2-f3 stops Ng1-f3, which is exactly what black wants to achieve. I think that white would seriously consider 1...Bg4 2.h3 Bc8 3.Nf3.


text:
How do I improve my checkmate skills?
I am able to develop my pieces systematically and purposefully. I am also good at defending my pieces. However, when the game gets closer to an end, I need to be able to see different mate variations easily. But alas I am having difficulty seeing them. As a result, I often start losing my positional advantage and win the game in more moves than it should actually take. Thanks in advance for your help!

Just so we're clear about what you're asking, do you want to improve calculating a mating sequence once you know there should be a forced mate, or are you looking for ways to improve your general attacking play?

I would like to be able to see forced mating sequences that are longer. I can see the mate if it is only 2-3 moves away. But I don't see forced mates that are more than a couple of moves. After the game I run an engine to see my performance and I see that my score towards the end of the game fluctuates a lot. It goes from +9 to +3 then +5 then +6 then +3 and so on. In other words, I guess I am looking for a little bit of both.

In that case, I suggest you keep this question about calculating mating sequences and asking another one about your general technique near the end of the game.

Do you know the basic checkmates K+Q, K+R, K+B+B and K+B+N?

Yes I am familiar with the basic checkmates.

The situation you find yourself in, is actually very common and also an issue for most amateurs. I think you will find out soon that there's no "one" answer that works for everyone. But there are of course suggestions that you may find useful:

Most promising way to improve your ability in finishing up games or checkmating, is solving puzzles. There are so many good puzzle books, websites/apps... you name it! Just start practicing and try to solve them, and in no time you will notice your improvement. Why it helps you may ask? think of it this way: Knowing how to finish games (or finding checkmates) means being familiar to the patterns present in your position (each game has its own details), and a pattern needs first to be noticed. To notice pattern/combinations/ideas, you first need to have been exposed to them in some way. That's what chess puzzles mainly do for you: they expose you to all sorts of ideas and force you to find them as otherwise you cannot solve the puzzle. Whereas just playing games over and over does not do the same for you, because there, you're not limited to one solution and instead of trying to find the right patterns(shortest finishes/checkmate paths) you just go with your already-made-intuition.
Second best suggestion I can think of, is reviewing your own games with an engine. Engines are in my opinion very much mis-used these days. They are amazingly productive when used to assist you while reviewing your already-played-games. With an engine, you will simply see where you may have missed out on some of the shorter paths towards finishing the game etc. Specially endgames where you have huge advantages, and you still find yourself playing out 20 moves, with an engine you will be fed the right ideas right off, so try to mull over them and don't just take them lightly. By doing this for most of the games you play, you will gather a very important amount of tactics/ or just useful ideas, that will help more easily concretize your advantages towards victories!

Some known and nice chess websites:

ChessTempo
ChessOK
Shredderonline
Sparkchess
Tactics and puzzles in chess dot com are great too.
Finally whatever phone you use, I'm sure you will find many free apps for chess puzzles.

Recommended chess books containing puzzles:

The Ultimate Chess Puzzle Book, very famous, written by John Emms
Another great one is, Garry Kasparov's Chess Puzzle Book, but of course it's not best if you just want checkmate puzzles.
A favorite of mine is, John Nunn's Chess Puzzle Book, which again is not only about checkmates, but instead contains all sorts of very advanced puzzles.
Of course the list can be very long, but do bear in mind that when it comes to checkmate puzzles, you don't really need to find the famous books, you just need any decent collection of them, (in any library you will find many relatively unknown puzzle books, that will perfectly do the job), as the idea here is to "gather as many ideas as possible" so in your own games you will notice and re-use the learnt patterns.

In order to conclude, the more puzzles you try to solve, the more games you study, the more you simply watch chess games, the richer your bag of ideas/patterns/combinations will become.

I'll try my best to answer this rather ambiguous question however I'd like to note that if you want help in chess your best bet is to familiarize yourself with terms like "tactics", "strategy" and so forth.
A little bit on 3 major terms in chess, or at least how I perceive them to be:

Tactics

patterns in chess(calculable) that lead to something factual such as winning a pawn, winning a piece, mating and so forth. Usually a forced sequence of moves.

Strategies

Really just the general plan you're following. If you try to pressure a certain square or use a sequence of moves to go on the offense and had that as your plan that's an implementation of a strategy.

Positional play

The most ambiguous term, it's generally just logical chess; Knights are strong in the center so you'd play your knight there if you had the opportunity. You don't follow a particular strategy nor did you calculate variations to see if this knight will lead to a definite advantage but because experience and general chess knowledge dictates knights are strong in the center you can conclude there is no downside to having it there, the opposite even.
All these terms can become moot easily, miscalculations, positional play that's not backed up by proper think-work and strategies that become invalid due to the opponent playing out his own game... You get the point.

So what we're looking for here is the term tactics, the pure act of seeing forceful moves that lead to a certain advantage. Tactics are something usually gained through practice and lots of experience, it also helps when you are familiar with the basic mates(mentioned before like King+Queen, King+rook, and King+2xbishop or King+bishop+Knight if you're feeling really up to the task) but also mates that simply involve certain patterns. Here's a supersimple one but you get the idea:
1K6/PPP5/8/8/8/4r3/3k4/8 b - - 0 1

There's a few ways to practice tactics:

Books

Books that involve endgames will always be great, they involve a great deal of tactics and will surely strengthen your ability to see them throughout the entire game.
Chess puzzle books are another great idea.

Websites

Let's not forget this great resource called the internet, there's websites out there with tactics trainers designed to take in account your playing strength as you do their puzzles. Two of these I'm aware of are:
www.Chess.com
www.Chesstempo.com
Especially Chesstempo is a great resource.

I have greatly improved my checkmate skills  by solving puzzles from John Nunn's 1001 deadly Checkmates book.I highly recommend this book.

This doesn't really add anything to this old question. This would be better as a comment on the accepted answer, but until you have enough rep to leave a comment, you should work on leaving good answers.

Solving tactics puzzles that end in mate should help a lot. Even if the puzzles are short (2-3 moves), you will learn all kinds of mate positions which is useful because you will know what to aim for in longer mate sequences.
In practical play, looking for long mate sequences is not necessarily the best choice, particularly if you don't trust your calculation skills. Often this happens when the mate requires you to make quiet (not forcing) moves or if you are under time pressure.
In some cases you might rather want to play a simple forced line that simplifies the position and leads to a clearly won endgame for instance.

I have found that the "Practice" section of Lichess.org has great examples, specifically because they guide you through standard Checkmating patterns (e.g. Boden's Mate, Arabian Mate, etc.) They also tell you how many moves you should make  for each of the problems (e.g. Checkmate in 3 if played perfectly), which I have found to be quite helpful. The site also has other helpful practice problems (tactics and pawn endgames), I highly suggest you check it out!


text:
Why is it rare to see unusual "special" opening preparation by trailing player late in a match?
Taking the recent Anand-Carlsen match as an example, I know that grandmasters spend incredible amounts of time in opening preparation, and Anand's play to refute certain lines of the Berlin defense was impressive.
But once reaching game 10, 11, or 12 and desperately needing a win, why don't players make an effort to force the game off into some opening line that the opponent almost certainly hasn't prepared for? Not into some fringe or unorthodox opening, but into solid openings that are just much less familiar for the opponent.
Much the same way that an American football team must spend at least some small amount of time practicing "trick" plays, like on-side kicks or throw-back passes, or much like a football (soccer) team might practice very special free kick formation for late in a game when a goal is needed very quickly -- shouldn't it be normal to prepare for a championship match by spending at least a small amount of time studying some very different openings that the opponent has not faced recently or does not appear to be as strong in?
I'm not endorsing these as candidates for specifically Anand v. Carlsen, but I might have expected to see some different variations of Sicilian, or to see Dutch Defense, Benoni Defense, or to see Reti opening, and to play in lines that don't transpose easily to positions that are similar to the main lines played (Grünfeld, Berlin, etc.).
I'm not saying Anand's openings were the problem in the match -- he often played well with great opening prep and blundered later on.
I am just asking why it is so uncommon to see players deviate to some "special preparation" in late stages of a match when they are trailing and need a win.
Wouldn't that be one of the scenarios that they prepare for specifically prior to the match starting? "What if I find myself down 1 point late in the match and my opponent has shown clear strength in the most frequent openings from the match? How will I steer the game into unknown territory?"

It happens, but there's a reason why it doesn't happen often, and, when it does, why it doesn't work.
First off, there's a psychological reason not to do it; it's uncomfortable. If the match is going badly for you, it's natural for you to fall back on familiar weapons: positions that you know how to play better than any others. When you do that, when you stand on familiar ("home," if you will) ground, you feel more secure and play better than if you're in less familiar territory. And when you play better, you're more likely to score better.
Also, there's the unknown. When you're down by a point late in the match, a single failure ends your chances. And, when you decide to divulge radically from your "normal" game approaches for this one game, you don't know with certainty how well your opponent can play those positions. So you divert time away from preparing to play comfortable positions even better than you currently play them (after all, no one plays their comfortable positions perfectly, there's always room for improvement) to learning how to play a completely different position passably well. And, when the day of the game dawns and you uncork it, you find out your opponent actually likes to play those positions, just never gets the chance to because opponents haven't so far let that happen. And down go your chances of leveling the match in a flaming crash.
Romantic notions like risking everything on one wild roll of the dice don't occur naturally to the vast majority of top chess players, because the tendency to do so keeps them from making it to the top, except in the rarest of circumstances.
A GM once told me chess was a little like tennis; "sometimes the only thing you can do is hit the ball back over the net and try to give your opponent another chance to make a mistake."
You're far more likely to see a player pull divergences like that that early in a match than late, such as Fischer pulling out 1.c4 to open Game 6 of the 1972 match (that match was for 24 games, so G6 there would have been like G3 of Carlsen-Anand). If it doesn't work, then the player still has the energy to save the draw if possible, and time to recover from the failure if not.

But even in a tennis match, there is the occasional need to change your serve when the opponent has demonstrated that if you use what you're comfortable with then she will crush it.

I think my question comes from a qualified position: Assume you have been playing the comfortable positions throughout the match, and you've been playing them well, but your opponent has repeatedly played them even better. You aren't looking to switch to someone unusual as a "roll of the dice" but rather out of complete necessity because it's clear your comfortable lines cannot beat this opponent. Then what do you do?

I looked through the WC matches since 1995 (Kasparov-Anand) to try to validate the claim that surprise openings aren't used very often at the end of matches. I found that generally this holds true, with some notable exceptions. Particularly, in both of his WC matches where he trailed with two games to go, Vladimir Kramnik has pulled out sharp tactical openings that he rarely or never played previously.
In 2004 vs. Peter Leko (http://www.chessgames.com/perl/chesscollection?cid=1002400) he was down 6.5-5.5 in a 14-game match when he played a Benoni in game 13. While he did not win that game, he generated excellent chances and likely missed a win in the endgame.
In 2008 vs. Viswanathan Anand (http://www.chessgames.com/perl/chess.pl?tid=65865), he was down 6-4 in a 12-game match when he played a Najdorf Sicilian in game 11. He did not win that game either, but he certainly avoided his renowned Berlin or the Petroff.
In 2013, Anand was down 5-3 going into game 9 of a 12-game match against Magnus Carlsen (http://www.chessgames.com/perl/chess.pl?tid=81142) when he played the 4. f3 Nimzo. He got a strong attack but ultimately blundered and lost the game.
However, there is an additional reason that surprise openings do not appear often, which is that many matches are level towards the end and both players want to get to the tiebreaks without expending too much effort. I find this to be the case in Kramnik-Topalov 2006, Anand-Gelfand 2012, and Anand-Topalov 2010 (although Topalov badly blundered in the last game and lost).
That leaves the following matches where a surprise opening did not appear: Kasparov-Anand 1995 (the last few games were sharp Sicilians, which had been played several times in the match already), Kasparov-Kramnik 2000, and Carlsen-Anand 2014. In Carlsen-Anand 2014, Anand had been getting good play from his openings as White and I see no reason that he should have deviated.
That leaves the only really inexplicable case as Kasparov-Kramnik, where Kasparov seems to have just lost his will to dominate after the match started out badly. He had been the dominant player in the world for over a decade and maybe finally being brought low was too fatiguing for him.

"both players want to get to the tiebreaks" … that was certainly not the case in Anand-Topalov. Topalov tried to avoid the tiebreak at all cost (quite sensibly, as he is unusually bad at rapid play for a top player and Anand unusually good), leading him to overpress and blunder. I also remember a case of "special" opening preparation from Topalov, when he was a point behind against Anand, a dubious exchange sacrifice, quite exciting to watch live: http://www.chessgames.com/perl/chessgame?gid=1581338

You're totally right. My mistake.


text:
Plans for White and Black in the Queen's Gambit Accepted
I often play this variation of the Queen's Gambit Accepted:
[fen ""]

1. d4 d5 2. c4 dxc4 3. Nf3 Nf6 4. e3 e6 5. Bxc4 a6 6. O-O c5 7. dxc5 Qxd1 8. Rxd1 Bxc5 9. a3 b5 10. Be2 Bb7 11. b4 Be7 12. Bb2 Nbd7 13. Nc3 O-O 14. Rac1

My question is, what are the plans for White & Black? I get a bit lost when I reach this position.
Also, any other tips on my opening would be most appreciated

I'm thinking about the merits of avoiding the Q trade using 7.Qe2, to maintain better winning chances.  Black can advance with 7...b5 and, if desired, 8...c4.  But is it really advantageous to open up the Q-side so early?  Black can also play 7...cxd4, but 8.Nxd4 looks comfortable for White.  Unless looking to draw, I think I would prefer 7.Qe2 to 7.dxc5.

I'm not an expert on this line, but one idea from "Study chess with Matthew Sadler" stuck in my mind: To play against the b7-bishop with f3 and e4. So that might be an objective for white. For black this is probably harder to archive, because the Nc3 is ready to jump into d5.
But this Nc3 instead of Nd2 gives black a different target: The square c4. Say after 14…Rc8 15.Nd4 Ne5 makes some sense, to jump into c4 and possibly acquire the bishop pair. Though after 16.Nb3 this doesn't yet work tactically, because of 16…Nc4 17.Bxc4 Rxc4 18.Na5 Rc7 19.Nxb5 …
So maybe 14…Rc8 15.Nd4 Nb6 is better, because on b6 the knight will be more stable. Then 16. Nb3 and possibly Nfd5 with the idea to exchange the Nc3 and go Bb7-d5-c4.
This was a bit of a stream of consciousness, but I'll try to sum up:

Playing f3 and e4 to blunt the bishop b7 is an idea.
The squares c5,a5 and c4,a4 are targets for the pieces. Especially the knights can be very annoying if they reach such a square.
There is always the idea of playing a4/a5 to try and liquidate the whole queenside, especially if there is still a rook on the a-file.
This might look like a very calm position, but with so many pieces still on the board, you should definitely look out for tactical possibilities.
If you don't find anything better to do, you can move your king closer to the centre: It is always possible, that some mass exchanges leave you in an endgame, where the king centralisation will be key.


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Beat the Polish defence
I was playing a game against a FIDE master which started with the Polish defence, Spassky gambit: 1. d4 b5 2. e4 Bb7 3. Bxb5 f5
[White "Bad_Bishop"]

[FEN ""]
1. d4 b5 2. e4 Bb7 3. Bxb5 f5

What are the main plans and variations?

You should probably exchange the rook for a knight + 2 pawns + exposed king, here's the line: 1.d4 b5 2.e4 Bb7 3.Bxb5 f5 4.exf5 Bxg2 5.Qh5+ g6 6.fxg6 Bg7 7.gxh7+ Kf8 8.hxg8=Q+ Kxg8 9.Qg6 Bxh1

I tried the line 1.d4 b5 2.e4 Bb7 3.Bxb5 f5 4.exf5 Bxg2 5.Qh5+ g6 6.fxg6 Bg7 7.gxh7+ Kf8 8.hxg8=Q+ Kxg8 9.Qg6 Bxh1 from the comments & gained dynamic equality.
The line from 1. d4 Volume 2 given by @magd gives a game more in my style & less in my opponent's, but only with a slight edge.

I have the book "1.d4 Volume 2" by Grandmaster Boris Avrukh in front of me. Not the line you're looking at but Avrukh says 3.Bxb5 Bxe4 4.Nf3 Nf6 5.0-0 e6 6. c4 Be7 7.Nc3 Bb7 is perfectly playable for Black.
Avrukh's mainline vs the Polish defence is 1. d4 b5 2. e4 Bb7 3. Bd3 (solidifying the centre and aiming to prove the centre pawns are better than the wing pawns.) Nf6 (3...a6 4.Nf3 transposes to the St. George defense) 4. Nd2 e6 5. Ngf3 a6 6. 0-0 c5 7.dc Bxc5 8. e5 Nd5 9. Ne4 Be7 10. a4 b4 11.Nfd2! (heading for c4 and and freeing the Queen on the d1-h5 diagonal) ... and eventually += on move 18. The main plan for White is to play with pieces in the free space in the centre and possibly aim to attack on the Kingside or fill the holes left behind in Black's pawn structure. For more details buy the book.

Your best bet here is 4.Nh3 so your opponent doesn't get a tempo with 4. ...fxe4
If he takes with his pawn 4. ...fxe4 You can simply continue 5.Nc3 followed by 0-0 and you're clearly better.
If he takes with his bishop 4. ... Bxe4 you can with no fear proceed with 0-0 and your knight will always pose a threat such as Ng5 attacking his bishop and with pressure on f7 and even e6 if he moves his d pawn, or Nf4 where your knight gets a secure,strong position but in that case you should be careful about his g pawn advancing. All things considered white is better in this position.

It is probably the worst response possible. You can accept the pawn with 4.exf5. Then, Black will play 4...Bxg2, then 5. Qh5. Black's kingside weaknesses will result in loss of material. Black is forced to play 5...g6, The following [best, probably] moves are:

fxg6 Bg7 7. gxh7+ Kf8 8.hxg8Q+ Kxg8

When Black's bishop captures on h1, then you can trap it with f2-f3. Stockfish evaluates the position at depth 22 as +2, approximately.
If Black does not go ahead with his plan of winning the exchange, with 4...Nf6 (prevents Qh5+), then you play 5.Nf3. Your rook is safe, you have more space, and Black's kingside has been weakened.
Stockfish evaluates the position as +4.4!?

In the other lines suggested, it seems that White has a large advantage.


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Is this line of the Grunfeld playable for White?
So, I was playing this line of the exchange variation of the Grunfeld: 1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. cxd5 Nxd5 5. e4 Nxc3 6. bxc3 Bg7 7. Bc4 c5 8. Ne2 O-O 9. Be3 Nc6.
[Fen "r1bq1rk1/pp2ppbp/2n3p1/2p5/2BPP3/2P1B3/P3NPPP/R2QK2R w KQ - 0 10"]

In my computer's opening book, the only recommended move for White is 10. O-O.
However, I want to know whether 10. dxc5 is playable?

The problem with this line is that this is exactly what Black is hoping for.
You give the center to "win a pawn", but Black has several compensation : first of all the black bishop on ...Bg7 is now very strong. Also with ...Qc7 follow by ...Rd8 black will win the d-file. If Black want then they can easily win back the pawn by the following plan : ...e5, ...Bf8 and ...Bxc5.

I tried this line out against a 1900 elo rated opponent. His next few moves were exactly ...Qc7 and ...Rd8. He didn't win the pawn back but got good piece activity, and the game ended in a draw.

The idea "...e5, ...Bf8 and ...Bxc5." seems extremely dubious to me. Not only Black is not garanteed to get their pawn back, moreover they lose time and weaken both the center (d5 in particular) and the kingside (all the dark squares). You rather focus on activity than on the meaningless Pc5. As often has not, the pawn sacrifice is made "definitive" by offering the pawn exchange ...b6 cb6 ab6 to open the queenside.

According to http://chessok.com/?page_id=352 this has been played five times (by weaker players) and gives black a very slight advantage (-0.11) after 10…Qc7.
So, depending on you level this is certainly playable. If you analyse it a bit you might even have practical chances to achieve an opening advantage. But probably black will just win back the pawn and you'll have to be careful not to just be left with your worse structure.


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What are the differences between the major online chess sites that allow to play?
I'm thinking of dedicating some of my free time to learn and play chess in a systematic and serious way and try to participate in a non-Internet tournament in a few months. I will take this activity as a hobby, but still want to keep it serious, cos I know that my progress will determine how much fun the thing will be.
I know that there are many websites that allow you play chess online, but I'm interested in what experienced users have to say about them taking in care my goals. I'm looking for a place that allows me learn, play and test myself giving me a kind of rating from which I could infer with more or less accurateness my FIDE ELO and then decide when I'm ready to spend time participating in a non-Internet tournament.

Nowadays there is really a abundance of good chess servers. And they are all relatively similar. I think you need a site where you can:

Play blitz chess
Play correspondence chess
Do tactics training
Learn via articles and/or videos

If you want everything on one site, www.chess.com is probably your best bet. As far as I know ICC, chess24, playchess and FICS don't have correspondence games. For beginners it is often hard to play blitz, and even later you might learn more from longer games.
The downside of chess.com is that the players are relatively weak. But if you are just starting out, this is not going to bug you for a few years.

Is www.chess.com one of the most popular chess server? Can I play games again peoples at almost every hour? Can you be more specific regards  why you said "The downside of chess.com is that the players are relatively weak"? I mean, what kind opponent (ELO FIDE or relative) I can hope easily find there?

Chess.com is immensely popular. (They claim 11 million users…). You can play 24/7 if you want to. I didn't use it too much and I never figured out how to get opponents stronger than, let's say, 2000 Elo. On ICC or chess24 on the other hand I play surprisingly often against IMs or even GMs, so that's where my personal preference lies. But as I said, I think having correspondence games as well, is important for beginners.

ICC had correspondence games back in ~2004-2005, did they get rid of them?

I recommend http://chesstempo.com with all my heart. It is free with no advertisements. The interface allows a large choice of board sizes and figurine fonts. You can play online against other people or against computers of various strengths even when people are not available. You can also do tactics training - the best site for this.

That site have ads

There is a small text ad on the home page but is there an ad when you actually play or do tactics? At chess.com you are bothered with ads while playing a game.

@user3456 If there is a small add, consider rewriting your answer to indicate minimal advertisement.  After all, minimal advertisement is better than intrusive advertisement.


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Chess books for master level players
Chess books written by Aagaard, Dvoretsky and Kasparov are suitable books for master level players. I have recently discovered the book Perfect Your Chess by Volokitin & Grabinsky which is similar in vein. What other chess books are suitable for master level players?
I use the term master level players to refer to players who are at a level equivalent to 2200+ FIDE rating. Books suggested should:

be suitable for a general master level player.
contain sufficient material that will stimulate a master level player.
be useful in the training of a master level player.

I'm not sure how good a fit this question is, but in any case, as there are tons and tons of such books that are potential answers and this could turn into a big list, I'm going to make this a community wiki question.

I doubt there are tons and tons of books for master level players. That's not a very lucrative target audience. Especially Workbooks for Elo 2300+ players are  quite rare, I only know about the Dvoretzky stuff, Aagaards new series and "Perfect your chess".

@BlindKungFuMaster, since the OP didn't rule out e.g. games collections, of which there are many that are well-suited to master-level players, I believe there are indeed a great many potential answers to this question. Not to mention opening tomes that might be of use to masters.

@ETD, Game collections where the games are not thoroughly analysed and annotated are not suitable for master level players. In this regard I can compare Kasparov's My Great Predecessors to Bronstein's Zurich 1953. I have also found that most opening books are either specific and thorough, or diverse and not thorough, which is not suitable to a general master level player.

Another question is what you regard as "master level" player. There is often a confusion because the USCF awards "master" titles to basically every decent club player.

@Nevermore, if you want to make your question more specific as regards exactly which sort of books you consider in scope, as well as exactly what class of player you intend to target, please do. It's your question, and that's what editing is for. As originally written, you left a great deal open to interpretation by the reader.

Openings:
Questions of Modern Chess Theory by Isaac Lipnitsky - a Soviet classic. Gets into the ideas behind opening theory in general.
For specific opening lines - the Grandmaster Repertoire series tends to be quite good.
Middlegame:
Dvoretksy's Analytical Manual - I didn't get too far through it but it is an incredible workout.
Endgame:
Dvoretsky's Endgame Manual, of course. If you learn everything in this book you will have endgame knowledge that far surpasses most masters.
Practical Rook Endings - Korchnoi. Quite expensive in this listing but I found one for $15 a few years ago.
Most books by John Nunn.
General:
Any well-regarded selection of annotated games from a GM is immensely helpful. Keres, Tal and Shirov's collections are great, to name a few.

Thanks for your response. I think that Questions of Modern Chess Theory is a great book and it is accessible by a large range of chess players. I have found it useful in other parts of chess and not only in opening theory. Practical Rook Ending's seemed promising and I should look at it again.

A few other good books targeting stronger players:
(1)  Imagination in Chess by Paata Gaprindashvili (master-level tactics problems)
(2)  How to Play Chess Endgames by Karsten Muller and Wolfgan Pajeken (a book about endgame technique, as opposed to endgame theory)
(3) Learn from the Legends by Mihail Marin (a study of world champions' play in position-types in which they were particularly strong);
(4) A Practical Guide to Rook Endgames by Nikolay Minev (lots of instructive material).
By the way, unless you are a rook endgame specialist and have mastered all the rook endgame material in Dvoretsky and the Minev book you should probably avoid Korchnoi's rook endgame book mentioned above, because Korchnoi's book is aimed at a really high level (more like 2400+ rather than 2200+).


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Recommend chess software for windows 8.1
I've been running an old version Chessmaster: Grandmaster edition on my windows 8.1 laptop when I found a bug (Chessmaster recommended an illegal move), and I thought it was time to change my software.
I'm rated around 2000 elo and would like a program that has tutorials (tactics exercises, annotated games, endgame courses etc.)
Any recommendations?
PS. I've checked that my Chessmaster program has all the latest updates from Ubisoft.

A very good piece of software would be ChessBase. Two good engines to run would be Houdini or Fritz (they are essentially indistinguishable to anyone below a super grandmaster standard, although Houdini is reputedly stronger). Besides playing against the engine, you could also store and analyse your games on them.
ChessBase is also the name of the company that produces it, i.e. it's a company that specialises in the development of chess programs, unlike Ubisoft, so you can expect a lot from them.

Lucas is a good software but in my opinion I would say that Chessmaster is better than Lucas. Well you can try Lucas and see...

Join chess.com and play against humans. Training against computer will not help your positional judgement which is what you need to improve to get you from 2000 to 2200.

Well, here I must ask you, suppose you are playing chess against someone of ELO about 2000-2200, can you tell whether you are playing against a human being or a machine?? Google "The Turk" and you will see that even chess masters could not say whether their opponent was a human or a machine.

So, if you cannot distinguish between a player and a machine, your answer is not valid and moreover, chess engines can be simulated to required ELO and style(defensive or attacking or sacrificial) while players have a particular style and ELO. To become a true master one must be able to play against all styles of chess, for which a chess engine can train a person better than a human opponent who is  susceptible to blunders.

I think its a good suggestion in general. Part of the reason why I asked for an engine is because Live Chess on chess.com operates time controls, which doesn't suit me when I want an ad-hoc game against the engine (I have a lot of family distractions. An engine doesn't mind me leaving it for a few minutes, but a real opponent would)


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Assigning Engines in Arena
How does one assign a specific engine to a specific color in Arena?  I load a PGN file and move to a specific point in the game.  At that time I want to assign Engine A to play black and Engine B to play white.  Then when I hit the calculate or demo buttons the game proceeds (after selecting "New Variation").  I've spent half the day searching for the answer with no luck.  Any guidance would be greatly appreciate.

Are you looking for setting up two engines playing against each other? In that case you can use the following in Arena 3.5: Engines > Tournament.

In Arena 3.5.1, go to Engines, load the engine that is playing on engine 1 first (by selecting the engine 1 Radio button at the bottom left of the dialogue box) then load the second engine on engine 2.
To Play The engines against each other,  click the analyse button


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Rating based off play level?
Is there a program that can tell your rating based off how well you play in the game? (NOT based on result). Thanks.

This is called Intrinsic Performance Rating.
There has been a Kaggle Competition in which the winner predicted the Elo on the basis of a single game with an average error of 150 points.
As far as I know there is no single piece of software that gives you these predictions, but the Kaggle Competition provides links to the code used by the participants.

+1 brilliant. I didn't know there was such a competition. Thanks for sharing!


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The most honourable way to lose?
When in a bad position, is it more honourable to resign or to face defeat? And if it is to face defeat then is there a time when resigning is considered an honourable thing to do, or is it always considered the cowards way out?

Throw the board ;)

Playing on in a hopeless position when it is clear to you that your opponent has the knowledge, skill and time to finish you off is never honourable. It shows a lack of respect.
If you have played your moves much faster than your opponent so that he is in serious time trouble and you aren't, then it is perfectly reasonable to play on. With just a few seconds left playing without increment he may not have enough time to deliver the coup de grace.
In the reverse situation where you are the one with very little time on the clock it is excusable but perhaps not particularly honourable to play on as you can always claim that with so little time to think the hopelessness of your position hadn't sunk in.
Note that positions where you have very few moves and so stalemate is a possibility are not hopeless. Nor are positions where, although material down and so expected to lose with best play, you have some prospects of counterplay in a double-edged position.

"Playing on in a hopeless position when it is clear to you that your opponent has the knowledge, skill and time to finish you off is never honourable. It shows a lack of respect." I agree in general, but I don't see it as entirely disrespectful in all cases. You may, for instance, want to see them deliver the win so that you can learn from their technique. However if you are just drawing out a position that both of you could win in your sleep just because you can then it'd probably be seen as disrespectful.

"Playing on in a hopeless position when it is clear to you that your opponent has the knowledge, skill and time to finish you off is never honourable. It shows a lack of respect." We all know what happened in Zurich 2014

It depends. When you are completely lost, and there is nothing interesting, you should resign. I say "nothing interesting" because it is etiquette to let your opponent mate you if he has a pretty force mate against you.


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Why did GM Kogan play such a bad opening in this 1997 game?
  [FEN ""]
  [Date "1997"]
  [White "GM Kogan"]
  [Black "IM Watzkin"]
  [StartPly "8"]

  1. Nf3 d5 2. c4 dxc4 3. Na3 a6 4. Nxc4 b5 5. Na5 c5 6. b4 cxb4 7. Qc2

The first four moves are common, but then ... 5. Na5 c5 6. b4 cxb4 7. Qc2
Why would a strong GM purposely go in to an opening that is so bad that it is already lost? After move 7 Stockfish evaluates the position as -1 or something like that.

Waitzkin analyses this game on youtube with Chessmaster edition. Do yourself a search and take a look!

The reason is probably that GM Kogan didn't have the opportunity to consult Stockfish during this game …
If you play unorthodox moves to pose unorthodox problems, sometimes you stumble yourself. And it's not like he played completely stupid moves. He sacrificed a flank pawn and has now a majority in the centre and b2 for his bishop. The knight on a5 at least hinders the normal development Bb7.
Humans don't play like computers. Of course he played risky and aggressive chess, but whether his opponent can punish him for it, is still entirely unclear at this point in the game.
If you take a look at Tal's games you might find that ideas don't have to be sound to be dangerous.

haha well, I was in inspired mode and played one of the MOST creative games of my career that brought me many compliments from genius creative GM as Benko (that watched the game LIVE) and few others too :-)  Not everybody can appreciate 'creative chess' or rather concrete chess with concrete ideas that created big problems and search for HARMONY (for a pawn gambit!)disturbing opponent's normal DVP, while fighting for big center etc and Josh was also shocked and even after the game didn't really appreciated what happened.. (he was 'too conservative' as a player and I could already feel he will never become a GM...) in one point I was with big edge close to winning, but did the old sin to enjoy the position too much and made a blunder... Greetings from Spain! Arthur www.olalachess.com

Great! Nice to hear your perspective, grandmaster.