# Question
Title: Does depth (number of ply) still matter once it is high enough?
*This isn't real, just imagine this happening.*

`Computer A` is supercomputer. It can calculate 30 ply deep within 20 seconds.

`Computer B` is supercomputer. It can calculate 15 ply deep within 20 seconds.

They play against each other chess.

Does these 15 depths really matter? I guess that within these 15 depths there may be trillions way to escape a checkmate or capture of important piece. Sure, `Computer A` knows more. But `Computer B` is able to predict future quite far too, in my opinion, far enough to defend himself really well.

# Answer
Yes, those 15 depths very much matter.

Consider this position that occurred in Kasparov's Immortal Game vs Topalov.

```
  [White "Kasparov"]
  [Black "Topalov"]
  [FEN "b2r3r/k4p1p/p2q1np1/NppP4/3R1Q2/P4PPB/1PP4P/1K2R3 b - - 0 24"]

```

I tested this position with several engines. Some engines, at depth 15, failed to detect that **24...cxd4** is a losing move and thought it was winning. Those same engines, at a greater depth, played the correct move **24...Kb6!**

For example, even an engine as powerful as Stockfish 4 initially at depth 21 thinks the losing move **24...cxd4** is correct.

```
Stockfish DD 64 SSE4.2: 24...cxd4 25. Re7+ Kb6 26. Qxd4+ Kxa5 27. Qc3+ Kb6
28. Qd4+ Qc5 29. Qxf6+ Bc6 30.Qxc6+ Qxc6 31. dxc6 Rd1+ 32. Ka2 f5 33. c7 Rc8
34. Rxh7 Rxc7 35. Rh6 Rc6 36. g4 f4 37. g5 Rd2 38. c3 Rxc3 39. Rxg6+ Kc5
40. Bg4 Rcc2 41. Rxa6 Rxb2+ 42. Ka1 Rbc2 43. Kb1
(-1.45/21)

```

The same engine, when kept on for a little more depth, shows **24...Kb6** to the correct move.

```
Stockfish DD 64 SSE4.2: 24...Kb6 25. b4 Qxf4 26. Rxf4 Nxd5 27. Rxf7 cxb4
28. axb4 Rhe8 29. Rxe8 Rxe8 30. Nb3 Re1+ 31. Kb2 Re2 32. Rxh7 Nxb4
33. Kc3 Nd5+ 34. Kd3 Rxh2 35. Rh4 Ne7 36. Nd4 Nc6 37. Nxc6 Bxc6 38. f4 Kc5
39. Be6 Rxh4 40. gxh4 Bd5 41. f5 gxf5 42. Bxf5 a5
(-0.78/26)

```

Fritz 11 SE, at depth 15, also failed. But it found the correct move at depth 16!

```
Fritz 11 SE: 24... cxd4 25. Qxd4+ Qb6 26. Re7+ Nd7 27. Qe5 f6 28. Qc3 Qg1+
29. Ka2 Bxd5+ 30. Nb3 f5 31. Qc7+ Ka8 32. Rxd7 Rxd7 33. Qxd7 Bxf3 34. Qd6 Qa7
(-1.44/15)

Fritz 11 SE: 24... Kb6 25. b4 Qxf4 26. Rxf4 Nxd5 27. Rxf7 cxb4 28. axb4 Nxb4
29. Nb3 Bd5 30. Rf6+ Nc6 31. Nd4 Rdf8 32. Rd6 Kc5 33. Rxc6+ Bxc6 34. Ne6+ Kd6
35. Nxf8
(-0.59/16)

```

Also consider this incredible problem like position that I found here.

Stockfish was not able to find the winning line 1. Be2+! until depth 31 and up until then it thought it was a bad move. I demonstrate the win here. The point is that Black is in zugswang because of mate threats and has to either give up the queen or move the a pawn which would allow White to create a passed pawn and win.

```
   [FEN "8/2p1q3/p3P3/2P4p/1PBP2kP/2N3P1/7K/8 w - - 0 1"]

   1. Be2+ $1 Kf5 2. Nd5 $1 Qxe6 3. Bd3+ Kg4 4. Be4 $3 Qh6 (4... Qxe4 5. Nf6+)
   5. Nf4 Qg7 6. Nd3 $1 Qxd4 7. c6 $1 a5 (7... Qxe4 8. Nf2+ Kf3 9. Nxe4 Kxe4
   10. Kg2 Kd4 11. g4 hxg4 12. h5 Ke5 13. h6 Kf6 14. Kg3 Kg6 15. Kxg4 Kxh6
   16. Kf5 Kg7 17. Ke6 Kf8 18. Kd7 Kf7 19. Kxc7) 8. b5 $1 a4 9. b6 cxb6
   10. c7 Qxe4 (10... Qc3 11. Nf2#) 11. Nf2+ Kf3 12. Nxe4 1-0

```

Here's the engine log from Stockfish 4. As you can see, it detects that 1. Be2+ is winning, only on depth 31!

```
Stockfish DD 64 SSE4.2: 1. Be2+ Kf5 2.Bc4 c6 3. Ne2 Qf6 4. Kg2 Kg4 5. Nf4 Qxd4
6. Bd3 Qe3 7. Be2+ Kf5 8. Bf3 Qd2+ 9. Kh3 Qxb4 10. e7 Qe1 11. Ne2 Qf1+ 12. Kh2 Qf2+
13. Kh3 Qe3 (-1.05/22)

Stockfish DD 64 SSE4.2: 1. Be2+ Kf5 2. Bc4 Qf6 3. Ne2 c6 4. Bxa6 Qxe6 5. Bd3+ Kf6
6. Nf4 Qe1 7. d5 Qxb4 8. dxc6 Qxc5 9. Be4 Ke7 10. c7 Kd7 11. Nd5 Kd6 12. Kh3 Qc4
13. Bg2 Qg4+ 14. Kh2 Qc8 15. Be4 (-1.15/26)

Stockfish DD 64 SSE4.2: 1. Be2+ Kf5 2. Bc4 Qf6 3. Ne2 c6 4. d5 cxd5 5. Bxd5 Qb2
6. Bc4 Kf6 (-1.01/28)

Stockfish DD 64 SSE4.2:  1. Be2+ Kf5 2. Nd5 Qxe6 3. Bd3+ Kg4 4. Be4 Qh6 5. Nf4 Qf6
6. Nd3 Qxd4 7. c6 Qxe4 8. Nf2+ Kf3 9. Nxe4 Kxe4 10. Kg2 Ke5 11. Kf3 Kf5 12. g4+ Kf6
13. gxh5 Kg7 14. Kf4 Kf6 15. h6 Kg6 16. h5+ Kh7 17. Kg5 Kg8 18. h7+ Kxh7 19. Kf5 Kg7
20. Ke6 Kh6 21. Kd7 Kxh5 22. Kxc7 Kg5 23. Kd7 (6.06/31)

```
> 14 votes

# Answer
The relationship between performance gains and search depth has actually been an active area of research for quite a long time in the computer chess programming communities. There was a theory that increases in search depth resulted in diminishing returns in strength... this seemed to be verified in experimental results.

From my perspective, there is an intuitive foundation for this. Imagine your hypothetical match up between two supercomputers, starting from endgame tablebase positions. Most forced wins in tablebases happen at a horizon less than (for instance) 50 ply. The majority of the remaining positions are drawn, only a small fraction resolve to wins at a higher depth. A computer searching at 100 ply would have limited advantage over a 50 ply computer, because (as you mention) the weaker program is able to navigate through nearly all the losing lines, all occurring at more limited depth. A 50 ply program would actually have a much bigger advantage over a 25-ply program... as would a 4 ply program have an even bigger advantage over a 2 ply program.

I first came across this concept about 15 years ago, in the series of papers on Dark Thought, experimenting in deep searches. These are a great read if you are interested in computer chess.

Although I couldn't find an online reference, there is a paper from last year on this topic...

Diogo R. Ferreira (2013). The Impact of the Search Depth on Chess Playing Strength. ICGA Journal, Vol. 36, No. 2
> 5 votes

# Answer
The question is: Do you mean 15/30 ply of exhaustive search, or a nominal depth/iteration of 15/30 of a modern chess engine like Stockfish?

If you meant the latter, 15 ply does not necessarily mean much. Modern chess engines heavily prune and reduce moves that are supposedly bad, so it might be that a sacrifice that seems to be bad at first sight, at a nominal depth/iteration of 15 is actually only searched to a depth of e.g. 5-10. At depth/iteration 30, the move probably is still searched only to a reduced depth, but then it might be an effective depth of 15-20, which could be sufficient to find that the sacrifice is actually good, and as soon as the engine discovers that the move is promising, it will decrease the reduction, so that the move is searched to a depth closer to 30 ply (or even deeper due to extensions and quiescence search). So yes, I think it can make a difference, even if the combination is within the nominal horizon of 15 ply.

If you were referring to an exhaustive search, then I think an engine with a depth of 15 would be very strong provided that it has a good evaluation function and some kind of quiescence search (after the leave nodes at depth 15). Due to diminishing returns, I think the gain by doubling the depth would be much less than what you would get for a match between two modern engines with depth 15 vs. depth 30. But that is of course only theoretical, since an exhaustive search to depth 15 would take several orders of magnitude longer than what engines usually take to reach depth/iteration 15, so such an experiment would only be feasible at lower depths.
> 2 votes

# Answer
FWIW When the ARM was new, I wrote an optimised ARM exhaustive search program with a material only position evaluation after ply 1.

I used tricks with optimised machine code, iterative deepening, alpha-beta windowing on sorted moves (almost all positions had value 0, so got near-optimal alpha-beta pruning) - and hash tables which reduced the branch factor to much less than the theoretical square root for alpha-beta, typically around 4 at the worst part of the game.

In a competition against the standard programs at the time, my E6P program got into terrible positions, but with an extra ply or two exhaustive search compared to pro software at the time (ie typically 6 ply exhaustive + quiescent search in the worst stage, with up to 12 ply as the game simplified), it kept wriggling out of actually losing, despite the confidence of its opponents. Almost all the games went to adjudication after many hours because the opposing programs couldn't actually win.

Later I optimised it for StrongARM, where it moved to 10 ply. This version could easily beat all the non-chess players, though obviously it lacked any strategy awareness, so the famous comment applied: yes, they are chess moves - but it isn't chess!

This was quite a few years ago, but I am tempted to try exhaustive again with a more strategic position evaluation at ply 1 - and with an Intel XEON theoretically 10,000-100,000x faster (and with 30k times more hash table memory) than a 4MIPS ARM2 Acorn Archimedes.

Admittedly not mainstream, but fun to play.
> 0 votes

# Answer
+1 ply is estimated +55..70 ELO gain (a lot of researches on this topic)

> I guess that within these 15 depths there may be trillions way to escape a checkmate or capture of important piece.

The thing is that all this "trillions" were calculated by A @ D=30, and if A choose move with winning eval, it mean that it calculated all this "trillions" and no matter which of "trillions" moves opponent reply - move is still winning
> -2 votes

---
Tags: engines, calculation, ply
---


title: To what depth has chess been solved?

text:
# Question
Title: To what depth has chess been solved?
Starting from the starting position, how many moves deep have we analyzed the possible continuations?

# Answer
Chess doesn't work like that. It isn't "solved" from the start position. It is "solved" from the end.

Currently chess has been "solved" for all positions where there are 7 or fewer pieces on the board.
> 3 votes

# Answer
Are you talking about Perft (https://chessprogramming.wikispaces.com/Perft%20Results)? Take a read on the article.

Don't use "solved", that's why you're getting negative votes, use "Perft".

To my knowledge, we have searched every single possibility up to depth of 15. Nobody has done 16 yet.
> 2 votes

---
Tags: theory
---


# Question
Title: How do you deal with the pinned knight on f3 in the Ruy Lopez (as white)?
I find myself in positions like this a lot when playing the Ruy Lopez:

```
[fen ""]

1. e4 e5
2. Nf3 Nc6
3. Bb5 d6
4. O-O Bg4

```

If I try to kick the bishop out with 5. h3, they back up to h5 and I'm in the same spot I was, essentially. What tends to end up happening is after my queen comes out, they take on f3 and I end up with doubled pawns, which makes me pretty uncomfortable on my King's side.

So what's the best way to deal with this pin? Or are doubled pawns a typical consequence of playing this line? Maybe I could have done something earlier? According to the chess.com database, this isn't a super common line anyway.

# Answer
> 10 votes
Black cannot exploit the pin with ...Nd4: not at once because the Nc6 itself is pinned, not later because c2-c3 is on your plan anyway. This means that you should not panic and can concentrate on developing before taking measures about the Bg4.

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

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

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

# Answer
> 0 votes
I'm not an expert on the Ruy Lopez, but it seems that its downsides outweigh the upside of potentially creating a doubled pawn on f3.

After 5. h3 Bh5, you are in fact not quite in the same spot: From h5, the light squared bishop can't assist to defend the light squares on the queenside anytime soon, so you can put *your* pin on the c6-knight to good use.

The weakness of c6 also allows you to easily get rid of the doubled-pawn threat because your queen can relocate with tempo (either by checking on c6, or d8 as soon as the d-file is opened).

For example:

```
[fen ""]

1. e4 e5
2. Nf3 Nc6
3. Bb5 d6
4. O-O Bg4
5. h3 Bh5
6. c3 Nf6?!
7. d4 {Threatening 8. d5.} a6 (7...exd4 8. cxd4 {Isn't prettier. Now a following Qc2 hits c6 and e4.})
8. Bxc6 bxc6
9. dxe5 dxe5 (
9. Qa4 {Another possibility.} Qd7 (9...Bxf3 10. Qxc6+ {Winning a pawn.})
10. dxe5!? Bxf3 (10...dxe5? 11. Nxe5)
11. exf6 {Hard to assess, maybe this line is a bit too risky.})
10. Qxd8+ Rxd8
11. Nxe5 Nxe4
12. Nxc6 {Looks fine.}

```

Of course, Black doesn't have to play Nf6, but any other move except 6...Qd7 or 6...a6 (e.g. 6...Be7) won't change anything essential. Black still has to deal with the pin somehow. 6...Qd7 only replaces it with another pin, while 6...a6 still allows the Qa4 manoeuvre. I'd be pretty comfortable with the situation as White.

---
Tags: opening, ruy-lopez, pins
---


# Question
Title: How to reply to an early c5 in the London System?
I've played the London System for about 3 months and am liking it alot, however I have run across several games where Black played a weird, but good, move early in the opening, c5.

example: `1. d4 d5 2. Bf4 c5`

Here, c5 is threatening to take on d4, a key position in the London System.

How does one play with a threatening move such as this with the London System, or what style of play has generally come of this move.

My last question, when Black plays c5, does this generally spell the end for typical London System lines, if played out with typical responses?

# Answer
> 5 votes
How you respond depends on your tastes.

If you like tactical play then 3. e4 is the Morris Gambit. This is basically the Albin Counter Gambit with colours reversed and an extra tempo. It can lead to very exciting play.

If you are more conservative and prefer a quiet life then 3. e3 is the normal move when play can quickly return to more normal lines.

---
Tags: opening, london-system, refuted
---


# Question
Title: Calculation and visualisation exercises - do they work?
I would like input from actual experience of improving calculation and visualization: can anyone testify to achieving actual and significant improvement in ability to calculate and visualize as a result of deliberately doing exercises set to train this skill? If so, if you could describe the delta of improvement (before, after), and the time it took, that would be appreciated.

My own definition of significant improvement would mean going from missing move possibilities that lie 4-5 moves down the road, to actually seeing them as almost as easily as if the position was on the board now.

# Answer
My performance rating was four to five hundred points above my actual rating in tournaments where I prepared primarily with calculation/visualization exercises; while tournaments without tactical training showed a performance rating closer to actual. So, I would say these exercises definitely make you sharper. There are permanent gains over time but I think you have to continue to use the ability or it will atrophy to some extent.
> 6 votes

# Answer
I have heard that solving chess puzzles is not exactly the greatest thing to do to help improve your chess game. That being said though, I myself have seen a major improvement once I started working puzzles on a regular basis. I would say that some of this is talent-based, however you can teach yourself pretty much anything you put your mind to.

My advice is this: Don't work yourself too hard with puzzles, if you do, you'll start making mistakes and bad habits. If you over do it, then you will become bored quickly, do just enough so that you improve a little, but don't try to make a giant leap in improvement in a short amount of time.
> 2 votes

---
Tags: training, calculation, visualization
---


# Question
Title: Please critique my game (Caro-Kann, Fantasy variation)
I'm an avid player of the , yet I recently came across the Fantasy Variation for the first time. Although I won, I wanted to post my game for review:

```
[FEN ""]
[White ""]
[Black "Bad_Bishop"]

1. e4 c6 2. d4 d5 3. f3 Qb6 4. Nc3 dxe4 5. fxe4 e5 6. Nce2 {I knew we came out of book here, but I didn't know how to exploit it. I ended up trading pawns as my e-pawn was hanging} exd4 7. Nxd4 Bc5 8. c3 (8. Nde2?? {This simple line is interesting, as it shows the pressure on white's game even at an early stage} Bf2+ 9. Kd2 Qe3#) Nf6 9. e5 Bg4 {This move helps develop my queenside, as well as trading down against the isolated d-pawn} 10. Be2 Bxe2 11. Ngxe2 Nd5 12. Rf1? {White begins a kingside attack when his king is still stuck in the middle} O-O 13. h4 Nd7 {I wanted to open the centre and attack white's king. This move aims to either win the e-pawn, or provoke e6} 14. e6 fxe6 15. Nxe6 Rxf1+ 16. Kxf1 Be3? {My eyes lit up when I saw the possibility of a knight fork on e3, but there is no way to force it. My thinking here was just to lay a cheapo trap and hope for the best} 17. N2d4 (17. Bxe3?? Nxe3+) N7f6 (17...c5 {Immediately after playing 17...N7f6 I saw 17...c5 instead, but I don't think it works here} 18. Nxg7 Kxg7?! 19. Qg4+) 18. g4? Bxc1 {OK, it turns out 16...Be3 wasn't so poor, as I can remove the defender of g4 and win a pawn} 19. Qxc1 Nxg4 20. Qg5 {From this stage of the game, white is treatening mate, so almost all of the following moves have to be checks} Nde3+ 21. Ke2 Qxb2+ 22. Kd3 g6 23. Qe7 {I missed this move, as I thought white would play 23. Rg1} Qxc3+ {Forced, intending to trade queens and win a pawn} 24. Ke4 (24. Kxc3 Nd5+ {White should have opted for an inferior endgame rather than letting his king be pulled up the board}) Nf2+ 25. Ke5 (25. Kf3 Nd5+ {This shows the difficulty white is in. He either faces mate or large material losses}) Nc4+ 26. Kf4 (26. Kf6 Ne4#) Qe3#

```

My questions are:

1. How could black have played better?
2. I played 16...Be3 as a 'cheapo', which my opponent didn't fall for. What would have been better than 16...Be3?

# Answer
> 2 votes
On move 6, I'm not really sure why White didn't just play Nf3. After that, Black should play exd4 Qxd4 followed by (after Qxd4 Nxd4) just Bc5.

After Nce2, well surely exd4 makes sense, but I think Nf6 should have been considered, attacking the e4 pawn. Notice that anytime dxe5? is played then you have Bc5, with that mate threat that you already diagrammed (Bf2+ Kd2 Qe3#), so therefore you didn't have to give up the tension so early with dxe4. Nf6 develops and attacks e4 which is a critical point (a critical point is an unprotected piece/pawn or a piece/pawn with the same number of defenders and attackers on it. A critical point can also be a king or just like in the caters somewhere where you have weak squares and stuff. Attacking critical points is a key concept in torturing opponents or putting pressure in strategic chess).

By the way, I think Be3 is a medium good move... You are establishing a piece on the enemy's third rank or your sixth rank, which can be so strong in some middlegame positions that it is worth sacrificing an exchange for that piece and a pawn or something. The only other move I can think of is Re8, because there is a critical construction on the e-file with 2 knights on the e-file.

A critical construction is a rank, file, or diagonal where there are 2 or more pieces in opposition or just like a lot of pieces (regardless of color) on the same rank/file/diagonal. Critical constructions are very good for finding important tactics or defensive tactical resources that can involve double attacks, skewers, interference, etc. Therefore I think Re8 instead of Be3 makes a lot of sense. You are creating a lot of tension on the two knights and activating the rook.

Here is a sample line. 16...Re8 17. Nxc5 Nxc5 18. Nd4 Qa6+ 19. Kg1 (all other moves like Kf2 and c4 are just a worse version) Qd3 20. Bd2 (Qxd3? Nxd3 and now you are attacking 2 critical points which is the b2 pawn and c1 bishop, and you can take advantage of the critical construction on the second rank with Re2. On top of that, your knights easily get to the sixth rank or other strong squares) Ne4 21. Be1 Qe3+ 22. Kh1?! (Kh2 is just more accurate) Bxf2 23. Qxf2 and this should win, and all of White's lines were backed up by an engine.

P.s. On move 18 you missed ...c5, removing the defender of e6.

P.s. I think understanding critical points is something you mind as well learn anyway, and a technically possible answer to how you could have played this better. I think the opening was fine but you should have played Nf6 instead of exd4, because Nf6 develops while attacking a critical point which is e4, and you have a strong critical construction on the c5-g1 diagonal and tactical pattern if dxe5 which allows Bc5 and stuff.

# Answer
> 0 votes
On move 5, capturing with the knight is what I would've done. On move 6 as white, I would have pushed d5, ..cxd5 7. exd5 leading to an obviously good position for white. Move 8. defending with the bishop would put a counter attack on both attacking pieces and making an exchange in the center of the board means the black queen would run with free development. Using this you can point out some errors with black as well.

---
Tags: opening, caro-kann
---


# Question
Title: Wrong lines of play to illuminate right lines
De Firmian's *Modern Chess Openings* is a good book. I like it. However, the book teaches right lines of play. It teaches few wrong lines.

Should one not also study wrong lines—the blunders, the pitfalls, in otherwise good openings—to learn why the right lines are right?

If so, then how can one go about studying the wrong lines?

```
[FEN ""]
[TITLE "Example: Sicilian Defense, Accelerated Dragon variation"]
[STARTFLIPPED "1"]

1. e4 c5
2. Nf3 Nc6
3. d4 cxd4
4. Nxd4 g6
5. Nc3 Bg7
6. Be3 Nf6

```

If an example helps, then see the defense diagrammed above. De Firmian gives Black the right moves in the right sequence, which is nice; but his book apparently lacks space to explain also why Black should not, say, venture Nf6 earlier than move 6. I believe that de Firmian knows why not, but his book is not conveying this knowledge to me.

This tells me that I am probably using the book improperly.

Merely memorizing the right moves seems insufficient. I wish also to grasp why wrong alternatives are wrong. By what method can I study wrong moves for this purpose? How do you do it, please?

(If you answer, then please feel free to give whatever example you like. You need not speak of the Accelerated Dragon. I have arbitrarily diagrammed the Accelerated Dragon merely to put a concrete opening on the board for purpose of illustration, in case this helps.)

# Answer
> 13 votes
A healthy approach towards learning openings is to retain the key ideas involved, and not to necessarily memorise move by move unless it's an extremely precise sequence in a very theoretical line (as is often the relevant case at high level chess). It's a bit analogous to how one would learn physics, by understanding the principles, drawing connections between them, learning to how reason with them and so on, such that ultimately, you can reconstruct theorems in your head, as opposed to memorising them symbol by symbol.

Now in chess, *understanding the ideas* in the opening phase simply starts by asking yourself questions when you're exploring an opening: for example: "what is the point of an early `h6` here? what I am preventing and why is it with such priority?" or "what is `Qc2` achieving in this situation? can't I achieve the same with `Qd3`?" or "Could I not have played `Nf6` first without loss of tempo?" and so on.

In trying to answer those questions for yourself, you will automatically uncover the pitfalls, or the wrong/less optimal alternative moves, without necessarily seeing them listed in a book. Now of course one can never exhaustively do so, as there are simply too many variations in each opening or certain very hard to grasp ideas involved, and that's why there are thick books written on almost every opening, but that said, the essential part of any improvement you are going to make, will result from the struggle of trying to understand a position on your own. It is this struggle that will form your mindset for how to reason about openings in general, one that will continuously evolve for as long as you study chess.

Now in order to find the answers to the type of questions I had mentioned earlier, you need to consider two important aspects: **a)** a general strategy in mind for what the opening is trying to achieve, **b)** a concrete assessment of the variations involved such that the strategy in a) can be efficiently implemented, i.e., avoiding redundancies or other loss of tempi, not creating weaknesses or easy targets, and worst case avoiding blunders. This is the part where engines can immensely simplify the task.

Both are equally important. Luckily, the bulk of opening theory we have stems from human play and not computers, meaning players at some point attempting to tackle a certain move differently by emphasizing a set of key new ideas. *Luckily,* because it means we have a chance of understanding them if we manage to trace the original ideas.

In your example: the essential part of the Dragon variation for black in the Sicilian is the fianchetto'ed bishop on `g7.` Simply put, unlike most other Sicilian variations where the dark-squared bishop has very little active scope (instead being developed as a purely defensive piece), the Dragon is an alternative that provides more active prospects for the bishop, with a safe developement (fianchetto - making it hard to trade/challenge the piece) and with a follow-up that emphasizes undermining white's dark square control. This is a rough sketch that goes along the point a) we were discussing above. Now more along point b), namely the more concrete aspects of the opening, contains the answer to your `Nf6` question: by not playing `Nf6` too early you i) entertain the possibility of potentially developing the bishop to `g7` with tempo, as it will directly eye the `d4` knight and ii) you prevent the option of an immediate `e5` from white. As you show, `Bg7` forces a reaction such as `Be3` and then you include `Nf6` (rendering immediate `e5` less critical after `Nxc6`, see diagram) Whereas with for example `5...Nf6` (so before the bishop), you allow white an easy path to playing `e5` closing down the long diagonal and dislocating your `f6` knight. The comparison is illustrated below:

```
 [title "Importance of early Bg7 in Dragon"]
 [fen ""]

 1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 g6 5. Nc3 Bg7 (5...Nf6 6. Nxc6 bxc6 7. e5 Ng8 {without tempo, white is free to develop aggressively, no tempo invested on Be3 or on the defense of e5} (7...Nd5 {with 5...Bg7 and Be3 included, this is a good gambit, with about equal play} 8.Nxd5 cxd5 9.Qxd5 Rb8 10.e6! fxe6 11.Qe5 {forking black's rooks : this tactical shot wouldn't be available after 5...Bg7}) 8. Bc4 Bg7 9. Qf3 e6 {rather forced} 10. Bf4 {white is objectively better as they have fully developed, they have the better minor pieces with central control, they have induced important dark square weaknesses in our position by forcing e6. Instead, black is critically under developed and without any real active prospects.}) 6. Be3 Nf6 7. Nxc6 bxc6 8. e5 Ng8 {the knight is retreated with tempo as e5 is under attack. Sure it's a bit slow, but black has a healthy pawn structure, a target on e5, and a relatively easy development to follow. Two main variations exist here, 9. Bd4 Qa5 and 9. f4 f6, see Kasparov-Ivanchuk 2002 for a nice example. }

```

So you see, by bearing in mind that with a tool such as the Dragon black intends to play actively and eventually for the initiative, and going through the respective variations of `5. Bg7` and `5. Nf6` we've come to the conclusion that `Bg7` *is* the key move here for black in order to not lose pace with white's development/play while keeping active prospects open (make sure to go through the Ivanchuk game I mentioned in annotations).

In fairness, there are much simpler examples to use for the purpose of our discussions. Let's choose a line in the queen's gambit exchange variation (see annotations for discussions):

```
 [title "example #2: queen's gambit exchange variation"]
 [fen ""]

 1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 exd5 5. Bg5 c6 6. Qc2 {One wonders, why Qc2 so early? as opposed to e3 for example. In the exchange variation, black often struggles to create active play, and one reason is the c8 bishop which has a hard time of becoming useful. Qc2 is played early to take away the only remaining active bishop move, namely, Bf5!} (6. e3 Bf5 {black has developed their only potentially poor piece in this variation, as it went unchallenged by white.})

```

In short, in the exchange variation white is committal about the centre early on (`cxd5`) and continues to play actively with `Bg5` forcing `c6`, followed by the simple usual setup of `e3-Bd3-Ne2-f3` setting up `e4` push (once castled of course) and a potential minority push on the queen-side. Concretely speaking, you want to achieve all this while not allowing black to develop easily or to create active play. So you start looking more carefully at the position, and only then realise the importance of nuanced moves such as `Qc2.` You may argue, why can black not play `g6` immediately after `Qc2` in order to revive the `Bf5` idea while preparing to fianchetto the `f8` bishop? whether or not a case can be made for that idea, the important thing is that this process of asking these kinds of questions and trying to find the answers to them on your own is how you should learn openings and how you eventually form a mindset for how to think about them in general such that you can even start developing your own systems for facing various things.

# Answer
> 7 votes
In essence this is why databases are used. No book has room for such data. Basically if someone leaves your preparation, you need to pause and ask "what is wrong with that move", or when studying lines ask yourself "what about x". Of course the more you know the less you have to think over the board -- so yes, study the refutations to inferior replies, etc. Using a chess engine can help too.

---
Tags: opening, opening-traps
---


# Question
Title: I wanted to understand the chess engine comparison. What does this result matrix show?
For example in the first row and second column, Stockfish vs Houdini, the result is 27-25+7-3=-16. I understand that 27 signifies Stockfish's number of wins+ draws, similarly 25 signifies that of Houdini. But what does "7-3" signify? and how is the result -16?

And what does the blank in Row 1, column 7 mean? similarly in (6,11), (7,1), (7,10), (7, 12), (10,7), (11,6), (11, 12), (12,7), (12,11). Do they signify that those matchups have never happened? If so Where should I look for if I want comparison of such matchups?

This question may be weird, but please at least guide me where should I ask these questions if not the answer.

# Answer
@muclux is right on the results. Check his comment. I'll answer what "16" mean.

Scroll further down on the page.

The number is the **rating change**. Stockfish lost 16 rating point to Houdini, similarly Houdini won 16 points from Stockfish (convince yourself by going to the Houdini vs Stockfish cell).
> 1 votes

# Answer
I believe the answer to the meaning of the numbers is at the top of the list above that matrix.

As for the blank spots, yes I believe those are for games which did not occur.
> -1 votes

---
Tags: engines
---


# Question
Title: London System with Nc3 -- what's the idea?
Recently top GMs are playing a London system type setup with Nc3 before c4. I can't imagine they are going for cheap tricks with Nb5, but I am not seeing a valid positional idea behind the move either. For example Carlsen-Ding 2017

```
[FEN ""]
1.d4 Nf6 2.Bf4 g6 3.Nc3 d5

```

# Answer
If you want to know whether the knight is badly placed on c3, you have to think about your plan. Normally, in d-pawn openings you want to play c4 to attack Black's hold on the center on d5. Here, this is not White's plan. Instead:

* White may want to play h4-h5 and attack Black on the kingside. This means White may want to follow up with Qd2 and 0-0-0.
* Another idea is the play a gambit with e4. If Black takes dxe4, the knight isn't so bad on c3.

The badly placed knight on c3 is a small price to pay for "getting it out of the way", since it wouldn't do much for the attack elsewhere (it's block in the queen's best square on d2, and a3 is an even worse square).

You are right that according to conventional chess wisdom, you shouldn't play like this. But this kind of system is not conventional! Highly creative players like Jobava play this way (In fact, this setup is named after Jobava). Check out some of his games here.
> 4 votes

# Answer
It's normal developing move after all. I doubt the knight stands there so badly. It keeps Bg7 stupid as c5 can now be hard for black to achieve. It controls d5 and e4. You probably don't see much point in white's play, but try to find what's black going to do. If you make weird looking move only to force opponent to do the same, your move is probably not so bad. I don't say it's briliant, but it doesn't look bad, too. The knight doesn't have to be there forever and black may be forced to make a lot of concessions too.
> 3 votes

# Answer
A black player who wants to play the King's Indian, but encounters the London instead, often chooses a system with the move ...d6. For instance, the book "Fighting the anti-King's Indians" by Yelena Dembo advocates such a system. The pawn on d6 restricts white's bishop on f4, and common white plans such as putting a knight on e5. This system scores very well for black.

With the move order 2.Bf4 3.Nc3, white threatens to play 4.e4, transposing into a Pirc. The move Bf4 isn't common in that, but Be3 and Bg5 are and they are often followed by a later Bh6 by white, so this system can transpose into a reasonably normal Pirc. That's an opening black may not want to play.

So black plays ...d5 to prevent e4.

As a result, Nc3 is in a slightly strange square, but Black has been prevented from playing his very favourable ...d6 setup and now has to make the slightly unusual combination of ...d5 and ...g6 work somehow. This is a little explored situation and the players are on their own. The best player is likely to win.

That's what Carlsen wants, as he is the best player.
> 3 votes

---
Tags: opening, london-system
---


# Question
Title: Is this endgame (sort-of Q vs K) a draw?
I think the following endgame is a draw.

```
[FEN "7k/5BpP/3K2P1/8/8/8/8/4q3 w - - 0 1"]

```

My reasoning: I'm playing white. I will only move my king, always. Black's king cannot move. If the queen decide to capture any of my pieces, I will take back, so that won't work. And the queen alone cannot checkmate me, but black cannot bring a piece to help, so it looks like it is a draw.

Is there any flaw in my reasoning, and if yes, what is the flaw? Is this endgame really a draw?

# Answer
> 21 votes
Here's a simpler way to see why it's winning for black: You're right that the queen cannot checkmate the king by itself, but it can *stalemate* the king \[\*\] (an example pointed out by Ionut Deaconu) and that's all we need here as that would force the bishop to move. Once the bishop moves it's clear that material loss is unavoidable as either the bishop \[\**\] or the `g`-pawn will drop.

\[\*\]: Take any queen vs king situation (relevant here as the bishop cannot move and thus unable to prevent the queen from shouldering the king to a stalemated situation).

\[\**\]: The idea here is that with a cornered king there's no way for the bishop to move to a square guarded by its king while still protecting the `g6` pawn.

Below a dummy example is showcased:

```
 [title "Stalemate the king to win, example"]
 [fen "7k/5BpP/3K2P1/8/8/8/8/4q3 w - - 0 1"]

 1. Kd5 Qe3 2. Kd6 Qe4 3. Kd7 Qe5 4. Kc6 Qd4 5. Kc7 Qc5+ 6. Kd7 Qb6 7. Ke7 Qc6 8. Kd8 Qd6+ 9. Kc8 (9. Ke8 Qc7 10. Kf8 {Alternatively any bishop move drops the g6 pawn. E.g., 11. Be6 Qc6+ 12. Ke7 Qe4} Qd8+ 11. Be8 Qd6+ 12. Kf7 Qf6#) Qe7 10. Kb8 Qd7 11. Ka8 Qc7 {King stalemate reached} 12. Bg8 Qc6+ 13. Kb8 Qxg6 {The win is trivial now.}

```

---

Additional clarifications in regard to the question asked by Ionut Deaconu in comments:

> Why 4.Kc6? You cannot push me to the corners after 4.Be8. If you want to try a zugzwang I can play Bf7 back.

The diagram above focused on the case where white tries to survive only by king moves (as is of particular interest to the OP). White can of course try to keep the king near the bishop on `f7` and make waiting bishop moves in order to avoid their king from being cornered altogether. However, this is to no avail as the queen will first start off by **disconnecting** the king from the bishop and only then proceed to **shouldering** the king towards a corner and achieve the king-stalemate scenario. The disconnect is easily achieved by maneuvering along the *dark* squares to enter the 7th row and then push the king out. Illustrative variations are shown below:

```
 [title "Variation in regard to questions in comments:"]
 [fen "7k/5BpP/3K2P1/8/8/8/8/4q3 w - - 0 1"]

 1. Kd7 Qe5 2. Be8 Qd5+ 3. Ke7 Qc5+ 4. Kd7 Qa7+ 5. Ke6 (5. Kd8 Qb7 6. Bf7 Qc6 7. Ke7 Qc7+ 8. Ke6 Qd8 {and we reach the wanted scenario again. For the rest see the main variation.}) (5. Kd6 Qb7 6. Bf7 Qc8 7. Ke7 Qc7+ 8. Ke6 Qd8 {Again the wanted scenario is reached, the rest is similar.}) Qc7 6. Bf7 Qd8 {The hard part, which is the disconnect, has been achieved once this scenario is reached, the rest is trivial now again as there are no more useful waiting bishop moves there to deal with. The rest of this variation may be done more optimally.} 7. Kf5 Qf6+ 8. Ke4 Qg5 9. Kd4 Qf5 10. Ke3 Qe5+ 11. Kd2 Qd4+ 12. Kc1 Qc3+ 13. Kd1 Qb2 14. Ke1 Qc2 15. Kf1 Qd2 16. Kg1 Qe2 17. Kh1 Qf2

```

# Answer
> 24 votes
According to the Lomonosov tablebases, it's mate in 40 for black. While the queen can't force mate by herself, she can force a zugzwang. In this case, when the bishop is forced to move to e8. Then, it's a matter of giving checks until the queen forks the king and bishop.

One of the longest variations given is as follows:

```
[FEN "7k/5BpP/3K2P1/8/8/8/8/4q3 w - - 0 1"]
[Result "0-1"]

1. Kd7 Qb1 2. Be8 Qb8 3. Bf7 Qb7+ 4. Kd6 Qc8 5. Kd5 Qc7 6. Kd4 Qc6 7. Ke5 Qd7 8. Ke4 Qd6 9. Ke3 Qe5+ 10. Kd3 Qf4 11. Kc3 Qe4 12. Kb3 Qd4 13. Ka3 Qd6+ 14. Kb3 Qc5 15. Kb2 Qe3 16. Kc2 Qa3 17. Kd2 Qf3 18. Kc2 Qe3 19. Kb2 Qd3 20. Ka2 Qc3 21. Kb1 Qd2 22. Bb3 Qb4 23. Ka2 Qa5+ 24. Kb2 Qb6 25. Kc3 Qxg6 26. Bc4 Qd6 27. Bd3 g5 28. Be4 Qc5+ 29. Kd3 g4 30. Bh1 Qa3+ 31. Kd2 Qb2+ 32. Kd3 Qb1+ 33. Ke3 Qxh1 34. Kf4 Qe1 35. Kxg4 Qe3 36. Kh4 Qg1 37. Kh3 Kxh7 38. Kh4 Kg6 39. Kh3 Kf5 40. Kh4 Qg4# 0-1

```

# Answer
> 12 votes
You're right, at the first sight it looks like a draw: Black's king is kept out of play and the Queen cannot checkmate alone. Black's only idea for a win would be to sac the Queen on h2 and try to promote the other pawn, but that's obviously impossible because of the White Bishop still in play.

However, there's a trick: White can be put in zugzwang by Black's Queen, which could force him to move the Bishop and lose material. For instance, if the Queen manages to push White's King to a8 with the Queen on c7, White need to move (and lose) the Bishop.

Bearing that in mind, White should try to keep his King on the d8, d7, or e7 squares, so that he can move the Bishop to e8 in case of zugzwang.

# Answer
> -2 votes
If black takes the bishop when it's on f7, white wins. If the king is on f7, the bishop on e8, and the queen on the a1-h8 diagonal, then black wins. The bishop has to be protecting the g6 pawn, otherwise, black takes that pawn and wins. If anything else, it's a draw.

EDIT: the starting position is in black's favor FEN: 7k/3K1BpP/6P1/8/8/8/8/4q3 w - - 0 1 PGN:\[Variant "From Position"\] \[FEN "7k/3K1BpP/6P1/8/8/8/8/4q3 w - -"\]

---
Tags: analysis, endgame, draw, fortress
---


# Question
Title: Which chess position requires the most moves to reach?
For each legal chess position there exist a shortest sequence of moves from the starting position to that position.

Which position requires the most moves to reach?

# Answer
This was published about in the latest entry of Tim Krabbé's Chess Diary. Harry Goldsteen has put some research into this and came up with a position which is reachable only in 185 moves:

```
[FEN ""]
[StartPly "371"]

1.a4 g5 2.Ra3 g4 3.h3 g3 4.Rh2 gxh2 5.Nf3 h1=R 6.d3 d5 7.Kd2 e5 8.Nh2 a5 9.Ke3 d4+ 10.Kf3 e4+ 11.Kg3 e3 12.Qd2 exd2 13.Rb3 d1=B 14.Bf4 b5 15.Nd2 bxa4 16.Rb7 Be6 17.Ne4 Ba2 18.Nd6+ Kd7 19.Nc8 Kc6 20.Nb6 Kb5 21.Be5 Bb1 22.Bf4 a3 23.Be5 a2 24.Bf4 a1=B 25.Be5 { As in the 183- and 184-move games, White makes many waiting moves. Black ´leads´, as Goldsteen puts it - he must play optimally, although some changes in move-order are possible for him, too. } 25...Kb4 26.b3 Kc3 27.Nd5+ Kd2 28.Nb6 a4 29.Nc8 a3 30.Nb6 a2 31.Nc8 Bb2 32.Nb6 a1=B 33. Nc8 Bc1 34.Nb6 Bc3 35.Nc8 Bcb4 36.Nb6 c5 37.Na4 c4 38.Nb2 c3 39.Kf3 cxb2 40.c3 Bdc2 41.Ke4 Ne7 42.Bc7 Nd5 43.Be5 Ne3 44.Bc7 Nd1 45.e3 h5 46.Be2 Qh4+ 47.Kd5 Na6 48.Bg4 hxg4 49.Kc4 g3 50.Rb5 gxh2 51.Rb7 Re1 52.Rb5 h1=R 53.Rb7 Nc5 54.Bh2 Ne4 55.Rb5 Ng3 56.Rb7 Rhf1 57.Rb5 Nh1 58.g3 { Now White has created the smallest possible box in which Black´s promoted Rooks and Bishops manoeuver like tar through a sieve. } 58...Ke2 59.Rb7 Kf3 { The black King makes room for the white Rook so it can go to g2. In the next phase, the black Rooks must leave the box, otherwise the white Rook cannot pass. } 60.Rb5 Bfc5 61.Rb7 Re2 62.Rb5 Ba2 63.Rb7 Bcb1 64.Rb5 Rc2 65.Rb7 Re1 66.Rb5 Ree2 67.Rb7 Bd2 68.Rb5 Be1 69.Rb7 Rc1 70.Rb5 Bc2 71.Rb7 Ra1 72.Rb5 Bcb1 73. Rb7 Rc2 74.Rb5 Rc1 75.Rb7 Bc2 76.Rb5 Bab1 77.Rb7 R1a7 78.Rb5 Ba2 79.Kd5 Ra1 80.Kc4 Bab1 81.Kd5 R1a6 { Now the white Rook can enter via a5. } 82.Ra5 f5 83.Ra1 Ba2 84.Rc1 Bcb1 85.Rc2 Qh5 { Or Qg4; the Queen must be able to reach e2 in one move. } 86.Re2 Bd2 87.Re1 Bc2 88.Rg1 Bab1 89.Rg2 { The Rook has arrived. } 89...Ra1 90.Kc4 Ba2 91.Kb5 Rc1 92.Kc4 Bab1 93.Kb5 Ra1 94.Kc4 Ba2 95.Kb5 Be1 96.Kc4 Bcb1 97.Kb5 Rc2 98.Kc4 Re2 99.Kb5 Bc2 100.Kc4 Rc1 101.Kb5 Bab1 102.Kc4 Ra1 103.Kb5 Rha8 104.Kc6 Bd2 105.Kb5 Re1 106.Kc4 Rg1 107.Kb5 Ba2 108.Kc4 Bcb1 109.Kb5 Rc2 110.Kc4 Bc1 111.Kb5 Re2 112.Kc4 Ree1 113.Kb5 Ref1 114.Kc4 Bc2 115.Kb5 Bd2 116.Kc4 Rc1 117.Kb5 Bab1 118. Kc4 Ra1 119.Kb5 Ba2 120.Kc4 Be1 121.Kb5 Bcb1 122.Kc4 Rc2 123.Kb5 Ke2 { The black King must enter the box now; his first goal is a3. } 124.Kc4 Kd2 125.Kb5 Kc1 126.Kc4 Re2 127.Kb5 Kd2 128.Kc4 Bc2 129.Kb5 Rc1 130.Kc4 Bcb1 131.Kb5 Rc2 132.Kc4 f4 133.Kb5 Kc1 134.Kc4 Rcd2 135.Kb5 Bc2 136.Kc4 Kb1 137.Kb5 Ka1 138.Kc4 Bab1 139.Kb5 Ka2 140.Kc4 Ka3 141.Kb5 Ba2 142.Kc4 Bcb1 143.Kb5 Rc2 144.Kc4 Rc1 145.Kb5 Bc2 146.Kc4 Ra1 147.Kb5 Bcb1 148.Kc4 Rc2 149.Kb5 { Only now can the black Queen treacle into the box. } 149...Qe2 150.Kc6 Qd2 151.Kd5 Qc1 152.Kc6 Re2 153.Kd7 Qd2 154.Kc6 Bc2 155.Kb5 Rc1 156.Kc6 Bcb1 157.Kd7 Rc2 158.Kc6 Qc1 159.Kd7 Rcd2 160.Kc6 Bc2 161.Kd7 Qa1 162.Kc6 Bcb1 163.Kb5 Rc2 164.Kc6 Bd2 165.Kd7 Bc1 166.Kc6 Ree1 167.Kd7 Rce2 168.Kc6 Bd2 169.Kd7 Bc2 170.Kc6 Qc1 171.Kd7 Bab1 172.Kc6 Ka2 173.Kd7 Ka1 174.Kc6 Ba2 175.Kd7 Bcb1 176.Ke8 Qc2 177.Kd7 Bc1 178.Ke8 Rd2 179.Kd7 Ree2 180.Ke8 Rfe1 181.Kd7 Rgf1 182.Bg1 f3 183.Rh2 Ba3 184.Ke8 Bcb4 185.Kd8 Ba5+ { and the diagram has been reached. }

```

This is the current record, but

> Goldsteen does not have proof that 185 is unsurpassable - in fact, he thinks it is likely that it *can* be surpassed.
> 10 votes

---
Tags: problems, records, retrograde-analysis
---


# Question
Title: Can White win in this game (Q vs R+N+P)?
Is there any percent chance for the white to win? Seems like greed for the opposite queen on behalf of sacrificing his pieces has cost him this game.

The view is from the white player's end.

# Answer
No, there is no chance for white to draw, let alone win, this game. In fact, if you enter this into an endgame tablebase it will tell you that it is mate in 13 moves with perfect play from both sides. One possible line is:

```
8/4K3/8/4Q3/8/4nk2/3p4/4r3 w - - 0 1

1. Qh5+ Ng4+ 2. Kd6 d1=Q+ 3. Qd5 Qxd5+ 4. Kxd5 Rd1+ 5. Kc5 Ke4 6. Kc6  Ne5+ 7. Kc5 Rd2 8. Kb5 Kd4 9. Kb6 Rb2+ 10. Kc7 Kd5 11. Kd8 Kd6 12. Kc8 Rb1 13. Kd8 Rb8++

```

Even if you don't have a tablebase, the position is quite obviously won for black. White's only hope in this position would be if he could capture the black pawn or if there was perpetual check. Neither of this is possible here, basically because all black pieces are working together and can protect each other and (and this is **important**), black is threatening a discovered check/pin which helps to prevent perpetual checks: basically if white checks with the queen black's knight can block the check, while at the same time giving check himself, thereby gaining a tempo for queening the pawn.

If you moved the white king away from this pin, it might very well be draw by perpetual check. For instance the same position with the white king on b8 is a draw.
> 8 votes

# Answer
If, as you claim, it's viewed from White's side, then the black pawn is almost promoted and according to Shredder, White will even *lose* in 13 moves or less.

<sub>(no time right now to analyze/post variations, sorry)</sub>
> 4 votes

---
Tags: learning, endgame
---


# Question
Title: What should be White’s move here in which each side has just a king and a knight?
```
[FEN "8/8/8/2k2N2/2n1K3/8/8/8 w - - 0 1"]

```

Is this position a draw?

# Answer
Most people agree that this is a draw due to insufficient material, but FIDE and some chess websites say that a mate is possible. Once you could also claim insufficient losing chances, but with increment clock, this rule has vanished.

To eliminate any possible mate, I would try to lose the knight. The best move is Nd6 and chase the black knight until the draw is agreed upon. An equally good move is Ne3 with the same objective.
> 8 votes

# Answer
If you have used up your clock time in this position, you have lost the game since a mate is possible.

If you have some time left and with increment clocks it is easy to make 50 moves and claim a draw (the opponent will normally agree to a draw long before).

If you are not in increment mode and have less than 2 minutes left, you may claim a draw and every arbiter will agree to it.
> 3 votes

# Answer
It's 99.99% a draw. The only reason why it's not 100% a draw is that if one side is just being lazy, they could be checkmated by the other side.

The mate would be the king in the corner, the knight right beside it, the other side's king 2 square in front of it, and the other side's knight on the only other square where it can check the enemy king.

FEN: 6nk/5N2/6K1/8/8/8/8/8 w - -

URL: https://lichess.org/editor/6nk/5N2/6K1/8/8/8/8/8\_w\_-\_-

(did the position on lichess)
> 3 votes

---
Tags: analysis, endgame, draw, knights
---


# Question
Title: Three Pawns for a Knight - Why Doesn't Stockfish Like it?
In a recent game I swapped off a knight for 3 pawns:

```
[Event "County Match"]
[Site "Deepest Darkest Southern England"]
[Date "2018.01.20"]
[White "English Player"]
[Black "Ian Bush"]
[Result "0-1"]
[FEN ""]
[StartPly "41"]

1.c4 Nf6 2.Nf3 g6 3.g3 Bg7 4.Bg2 O-O 5.O-O d6 6.Nc3 c5 7.a3 Nc6 8.Rb1 Bf5
9.d3 Nd7 10.Nd5 Nb6 11.Ne3 Bd7 12.b4 Qc8 13.b5 Nd4 14.Nxd4 Bxd4 15.a4 Bh3
16.a5 Bxg2 17.Kxg2 Bxe3 18.Bxe3 Nd7 19.Bh6 Re8 20.Qd2 Nf6 21.h3 Qf5 22.e4
Nxe4 23.dxe4 Qxe4+ 24.Kh2 Qxc4 25.Rfe1 Rad8 26.Re3 f6 27.Rbe1 e5 28.Rd3
Re6 29.Rc3 Qxb5 30.Qd5 Rde8 31.Rb3 Qc6 32.Qxc6 bxc6 33.Rb7 R6e7 34.a6 Kf7
35.Be3 Ke6 36.f4 Rxb7 37.axb7 Rb8 38.Rb1 a5 39.fxe5 fxe5 40.Kg2 a4 41.Kf2
a3 42.Ke2 a2 43.Ra1 Rxb7 44.Rxa2 c4 45.Kd2 d5 46.Kc3 Rb3+ 47.Kd2 d4 48.Bf2
Kd5 49.Ra5+ Ke4 50.Rc5 c3+ 51.Kc1 d3 52.Rxc6 d2+ 53.Kc2 Rb2+ 54.Kd1 Rb1+ 0-1

```

I've started here as this was the plan after Qf5, and I played this way as I thought it a good way to get winning chances - it was a match and as it all looked fairly even wins were the order of the day. But Stockfish really doesn't like it, putting me down ~1.5 pawns, and I don't really understand why. Can somebody turn the "thoughts" of the metal monster into human terms for me?

# Answer
> 8 votes
Counting material is only one portion of evaluating a position. Stockfish considers space, piece mobility and activity, king safety, etc.

All of that produces an evaluation of the position, and for this one SF grades it (using LiChess) as about +2.2 (depth 31).

I note that before your knight sac Stockfish thinks you were already down by about 1.2, despite roughly equal material. That bishop on h6 controlling your weakened dark squares, for example, is clearly worth more than your knight.

As for your decision to sac the knight, from a practical point of view it seems a reasonable choice in a bad situation, because if you simply move your queen to e6 or e5, as SF suggests, white has a clear and natural plan of f4 followed by eventually opening up that file, and your clumsy rooks will not be nimble defenders.

SF suggests for white an immediate b6 after your queen takes on c4, and with that you will not get the pawn storm as you did in the game. White will have an open line to invade with his rooks (which one depends on your reaction to b6) and his extra piece will tell.

# Answer
> -2 votes
Well, sometimes knight are useful to fork pieces and stuff, but 3 of your pawns for a knight, in this position, is bad because now black has two connected passed pawns that could be put into good use during the endgame.

---
Tags: engines, analysis
---


# Question
Title: Which opening will develop both bishops like the following diagrams?
I'm looking for a chess opening that would result in something similar to the following end-positionings:

A nice open diagonal for the bishops.

or maybe the other way:

Also, what are the strengths & weaknesses?

# Answer
> 5 votes
As far as putting your light-squared bishop in d3 with an open diagonal is concerned, you could look at the London system as an example. The difference with respect to your first diagram is that the dark-squared bishop goes to f4 and the b, c, and d pawns stay one square behind.

Getting your pawn to d5 in the opening can be difficult because Black has to allow it; in many queen's pawn openings black replies ...d5 on move 1 or 2. One example where Black doesn't is the king's indian defense, but in that one Black quickly takes control of the a1-h8 diagonal which can stop you from opening it safely (you could start with 1.b3 to take that diagonal first, but then you are unlikely to be able to complete the rest of your plan).

In short, I think it's unlikely that you'll be able to develop in such a way. Five out of your first seven moves are pawn moves and Black has lots of ways to interfere with your plan.

(I see now an answer that does get the bishops where you want to, but at the cost of two pawns. Not sure if that's a price you are willing to pay.)

# Answer
> 9 votes
Danish Gambit is a possibility. There is **no free lunch**, no strong players will allow you develop your bishops like what your described without any compensation. You will need to gambit two pawns for this line.

From wikipedia

# Answer
> 3 votes
It is quite meaningless to discuss openings for one side only. Any opening between reasonably advanced players is always a struggle for an advantage and black has many ways to interfere with your plans.

Taking your first diagram for instance as an example, with the same number of moves (7), black could for instance achieve the following setup:

```
rnbq1rk1/ppp3bp/3p1np1/3Ppp2/2P5/1P1BP3/PB3PPP/RN1QK1NR w KQkq - 0 14

```

which looks perfectly fine to me. White's bishops are not all that much threatening anymore and black has good control of central squares and potential for a king side attack. You can get a similar setup for your second example.

If you do want to play an opening without having to care what black does (a so called *system opening*), I suggest to look into the **Colle-Zuckertort** system

```
8/8/8/8/3P4/1P1BPN2/PBPN1PPP/R2QK2R w KQkq - 0 1

```

or **King's Indian Attack** like structures, both of which might appeal to you.

---
Tags: opening, bishops
---


title: What is the "increment" in chess?

text:
# Question
Title: What is the "increment" in chess?
I saw this in many online games, but I do not understand how it works. With every move we can gain time, but what is it dependent on how much we get? Can please somebody explain the system behind it.

# Answer
Take a look at Wikipedia's time control article:

> **Fischer delay (or time increment)**, invented by Bobby Fischer. When it becomes a player's turn to move, the delay (or increment) is added to the player's remaining time. For example, if the delay is five seconds and the player has ten minutes remaining on his clock when his clock is activated, he now has ten minutes and five seconds remaining.

And in the usage of chess servers:

> On chess servers (like Internet Chess Club and Free Internet Chess Server) the time control is usually expressed with a formula: time+increment. Where time is a fixed amount of time (in minutes) assigned at move 0 for the entire game, and increment (in seconds) is the amount added after each move.
>
> When the increment is 0 the time control turns into a sudden death: so a 5+0 game is a game with sudden death at 5 minutes.
>
> When the increment is bigger than 0 the time control is a Fischer delay: e.g. a 2+12 is a game with Fischer delay with 2 minutes + 12 seconds each move.
>
> A game can even have a time set to 0: the clock is set to 0 and started after the first move with the increment only on both sides, and each move each player is granted only the increment: a 0+10 is a game where after the first move each player has 10 seconds to move.

---

**To sum it up:**

Time increment gets added to your current time to compensate for a probable delay (for humans is the reaction time and for servers may compensate for latency etc.). If you are fast enough to play your move before the increment ends, the extra time gets added to your current time thus augmenting your remaining time.
> 13 votes

# Answer
I second John Moutafis' answer. The increment here is always the time which is basically for a few secs like 3, 5, 10, 15, 30 or may be even longer in some cases.

Now, why this increment and how this works. When two players play a game with a time limit on the clock, the time decreases.

For example, playing in Chess.com with a time of 5 mins each for both players. So total time is 10 mins. Within this stipulated time, each player can think of the moves. Now, because of this limited time, both players have to be careful not to lose the game on time and make sure they play the best moves from their own side. Now, as we all know, chess requires thinking, so either player can run out of their clock if they tries thinking too much deep. Even you will see that 1000s of games are being lost by top players because of time deficiency.

Hence, if you have an increment on your clock, you would see that during endgames, the players take a refuge and they are able to play better and never become nervous due to the time factor. Understanding how the increments happen is on every move each player gains a respective number of secs.

Let's assume that the game lasted for 40 moves each for either player and then one resigns. So 40x3 (increment time value in secs) = 120 secs or 2 mins extra both players get on their clock which makes the game a bit longer and the players were able to perform better. At least I would suggest playing with some time increments in any chess website and you would feel the difference yourself.
> 2 votes

# Answer
Nobody mentioned that you have to be quick enough. So if the increment (or delay or bonus) is 5s, the effect is when your turn comes and you move within the increment value of 5s, you gain 5s. If you make a move after that 5s has passed, nothing gets added. Example, your, say at 17th turn, you have 4:07 left on your clock. You starts to think and after 2s, when your clock is left with 4:07-:02=4:05 you move. Your clock increases to 4:10 from 4:05. On the other hand, if you make the move after 6s, when the clock is at 4:01, it remains at 4:01.

Why the term 'delay'? Not sure. The effect is not same if the clock starts with a delay of 5s. So if you move within that, the clock remains same and if not it starts counting down.
> 0 votes

---
Tags: rules
---


title: Taking notes of time usage during game

text:
# Question
Title: Taking notes of time usage during game
While I know taking making any notes during a game is against the rules (and Wesley So was disqualified for this), does this include denoting the time usage after each move?

# Answer
> 15 votes
FIDE rules allow you to record the time:

> 8.1.4 The scoresheet shall be used only for recording the moves, the times of the clocks, offers of a draw, matters relating to a claim and other relevant data.

https://www.fide.com/fide/handbook.html?id=208&view=article

USCF rules also allow you to record the time:

> 20C. Use of notes prohibited. The use of notes made during the game as an aid to memory is forbidden, aside from the actual recording of the moves, draw offers, and clock times, and the header information normally found on a scoresheet.

U.S. Chess Federation. United States Chess Federation's Official Rules of Chess, Sixth Edition (Kindle Locations 1925-1927). Diversified Publishing. Kindle Edition.

---
Tags: rules, time-management, wesley-so
---


# Question
Title: Which chess variant has the largest board?
The largest I could find was for Double Chess, with a 16x12 board. Is there a variant with a bigger board? It doesn't have to be a variant in which chess pieces follow their orthodox movement rules.

# Answer
From wikipedia(emphasis is mine):

> **Infinite chess** is any of several variations of the game chess played on an unbounded chessboard. Versions of infinite chess have been introduced independently by multiple players, chess theorists, and mathematicians, both as a playable game and as a model for theoretical study. It has been found that even though the board is unbounded, there are ways in which a player can win the game in a finite number of moves.
> 5 votes

# Answer
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.
> 4 votes

# Answer
Another contender is Kubikschach. A 3-dimensional variant played on an 8x8x8 board (512 squares total)
> 3 votes

# Answer
Suppose we only allow chess pieces (so excluding all shogis) and only a 2-dimensional board. Then there are:

* Double Chess (II) (Hayward, 1916) (16 files x 12 ranks = 192 squares)
* Fortress chess (16x16 minus 8x2 off the centre of each side = 192 squares)
* Four-handed chess (many variants use a board 14x14 minus 3x3 off each corner = 160 squares)

s: David Pritchard. The Encyclopedia of Chess Variants. pub. Games and Puzzles Publications.
> 1 votes

---
Tags: chess-variants, chessboards
---


title: Chess tactics training software

text:
# Question
Title: Chess tactics training software
Is there a software/app/website to train chess tactics (forking, pins, deflections, decoys, overloading)?

Please help!

# Answer
There are many websites that offer tactical problems. A few allow an unlimited number of tactics without having to pay.
> 6 votes

# Answer
Best software I've ever seen for this purpose: CT-Art from Convekta. It's amazing. It's based on Blokh's tactical manuals, gives you positions to solve, and hints when you fail to solve them. And it's cheap (I've seen it new for $20 or so).

Best. Tactics. Software. Evar.
> 6 votes

# Answer
I would recommend lichess, as it's just completely free to do chess tactics whenever you want and everything else.

https://lichess.org/
> 3 votes

# Answer
Garry Kasparov's MasterClass at https://www.masterclass.com/classes/garry-kasparov-teaches-chess has some great examples.
> 1 votes

# Answer
Chess Hero is a good program with computer analysis, but you have to provide your own pgn file(s).
Any pgn reader will display pgn files, but a chessbase reader allows for special question-based training.
> 1 votes

---
Tags: software
---


# Question
Title: Why do we increase depth of search for a mate detection in alpha beta pruning?
I was following a tutorial for making a chess engine and in that, while writing the alpha beta pruning function the tutorial before checking for all possible moves generated , checks weather the current side is in check or not. If in check the depth was increased and i couldn't understand the reason. I am fairly new to chess engine programming and have searched about this but couldn't find anything relevant. Any help will be much appreciated.Thanks.

Here is the code for alpha beta pruning.

```
function AlphaBeta(depth, alpha, beta)
{
    SearchController.nodes++;
    if (depth <= 0)
    {
        return Evaluate();
    }

    //fiftyMove rule or if a position is Repeated
    if ((IsRepeated() || GameBoard.fiftyMove >= 100) && GameBoard.hisPly != 0)
        return 0;

    if (GameBoard.ply > MAXDEPTH - 1 )
        return Evaluate();

    //this is the line i am talking about
    var InCheck = SqAttacked(GameBoard.pieceList[Kings[GameBoard.side] * 10] , GameBoard.side ^ 1 );
    if (InCheck)  {
        depth++; //<---------HERE
    }

    var score = -INFINITE;

    GenerateMoves();

    var Move = NOMOVE, MoveNum = 0, BestMove = NOMOVE;
    var legal = 0; // To see weather any legal moves are possible
    var start = GameBoard.moveListStart[GameBoard.ply], end = GameBoard.moveListStart[GameBoard.ply + 1];

    for(MoveNum = start; MoveNum < end; MoveNum++)
    {
        Move = GameBoard.moveList[MoveNum];

        if (!MakeMove(Move))
            continue;

        legal++;

        score = -AlphaBeta(depth - 1, -beta, -alpha);

        TakeMoveBack();

        if (score > alpha)
        {
            if(score >= beta)
                return beta;

            alpha = score;
            BestMove = Move;
        }

        console.log('For move : ' + PrMove(Move) + ' Score : ' + score );
    }

    if (BestMove != NOMOVE)
    {
        StorePvMove(BestMove);
    }

    if (legal == 0)
    {
        if (SqAttacked(GameBoard.pieceList[Kings[GameBoard.side] * 10] , GameBoard.side ^ 1))
        {
            return MATE - GameBoard.ply;
        }
        else return 0;
    }

    console.log("");
    console.log("Best Move at Height : " + depth + ' Move : ' + PrMove(BestMove) + ' Score : ' + alpha);
    return alpha;

}

```

# Answer
> 5 votes
I can see more than one reason for that.

One reason is that after a check there are very few moves available: usually there are 30 moves available, but after a check there are usually at most 4 or 5. So that move doesn't count as a full ply if you want to measure the size of the resulting tree, and in the same search time you can go deeper.

Another reason, and I think it is the most important, is that a check is a forcing move, and consequences of a forcing move must be considered more deeply. So it is good to go deeper after a check.

Note that in this way, the program will tend to analyze all forced sequences of consecutive checks very deep, in this way it can easily find all perpetual checks and many forced mates. So this is can be very useful.

# Answer
> 5 votes
This is known as **Quiescence Search**.

> The purpose of this search is to only evaluate "quiet" positions, or positions where there are no winning tactical moves to be made. This search is needed to avoid the horizon effect. Simply stopping your search when you reach the desired depth and then evaluate, is very dangerous. Consider the situation where the last move you consider is QxP. If you stop there and evaluate, you might think that you have won a pawn. But what if you were to search one move deeper and find that the next move is PxQ? You didn't win a pawn, you actually lost a queen. Hence the need to make sure that you are evaluating only quiescent (quiet) positions.

---
Tags: engines, chess-ai
---


# Question
Title: Can one use alternative identifiers (from languages other than English) for chesspieces in PGN?
I came across this in the PGN standard on this site, section 17, for alternative piece identifiers (emphasis mine):

> English language piece names are used to define the letter set for identifying chesspieces in PGN movetext. However, authors of programs which are used only for local presentation or scanning of chess move data may find it convenient to use piece letter codes common in their locales. This is not a problem **as long as PGN data that resides in archival storage or that is exchanged among programs still uses the SAN (English) piece letter codes: "PNBRQK".**

Followed by a table of symbols for different languages.

The first part seems to suggest that one can use identifiers from other languages to represent the pieces if one so wishes.

However, the highlighted part seems to contradict that, saying that, ultimately, the PGN should use the English identifiers and not those of any other language.

It appears that a mistake in my understanding caused this contradiction, so I'd be glad if someone could please clarify it.

### My question

Can one use symbols from languages other than English for representing pieces in a PGN file?

Would something like this work (using the piece identifiers in German)?

```
[Event "Casual game"]
[Site "Hogwarts"]
[Date "2018.03.09"]
[Round "1"]
[White "Malfoy, Draco"]
[Black "Weasley, Ronald"]
[Result "*"]
[TimeControl "1/15+1"]
[FEN " "]

1. e4 e5 2. Sf3 Sc6 3. Lb5 Sf6 4. O-O Sxe4 *

```

# Answer
I read it like this:

> The standard is to use the English piece names. Of course, we can't stop authors to adapt this standard in their own programs (sometimes, it might make sense). But pretty please, do always stick to the English names for any data that might be shared between multiple programs.

For example, if I write a program to automatically scan games from old German chess magazines, it makes no sense to let my program try to parse the standard PGN piece names. I'd use German piece names instead, and this is fine in the environment of my own program.

But as soon as I want to store the PGN files in a database, I must translate them to English piece names or my database browser or whatever other program won't be able to read them.
> 4 votes

# Answer
The specification you have in your link has no practical meaning as the format is not enforced consistently. Steven J. Edwards introduced the format, but he didn't have authority to control how programmers implement PGN.

**Most PGN parser would only support the English language.**

I've been distributing PGN parsing softwares for years, but I don't think I'll add foreign language support. I assume anyone who is intelligently capable of playing chess would be able to read English piece identifiers.
> 4 votes

---
Tags: pgn
---


# Question
Title: Why is en passant possibility recorded in FEN regardless of whether there is a pawn ready to make the capture?
If a pawn has just moved two squares ahead, one records the square right behind it in the part of FEN for recording en passant possibility, regardless of whether there is a pawn of the opposite color ready to make the capture.

For example, the FEN for the position after 1. e4 is:

```
rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1

```

## My question

Why is this done? It sounds superfluous, since an en passant capture can be made only on the very next move of the opponent's, so recording it as such when there is no pawn in position to make the capture seems unnecessary.

Is there some historical or technical reason for this?

# Answer
> 5 votes
Easier for everybody. No need to check enpassant possibility.

---
Tags: history, fen
---


# Question
Title: The principal variation is always wrong!
I read in an internet blog that when analyzing my games with an engine, it is often useless to copy the principal variation to my annotations, because (they say) it is well known that the principal variation is almost always wrong. By this, they mean that the principal variation often does not contain the best moves from both sides, as one would expect.

I am thinking about this and I am trying to understand what they really mean and why is it so. I can see two reasons:

1) If I analyze at 20 plies depth, then the fifth move in the principal variation was probably analyzed only at 10 plies depth, so it is less reliable than the first move. This probably does not apply very much to tactical positions, where, thank to quiescence search, positions are analyzed deeper when needed.

2) The engine is optimized to find the best move, but it doesn't care to find the best principal variation. This can be relevant when alpha-beta pruning is combined with aspiration window heuristic and incremental search.

Imagine that the engine first analyzes at 10 plies, and it finds that the best move is evaluated at +0.50 and the other moves are all less than +0.20. When increasing the search depth to 18 plies, the engine can analyze the best move with an aspiration window between +0.20 and +0.40, asking the search to find the exact value only if lies in the interval, or a cutoff value if it lies outside. If the search finds that the best move is valued more than +0.40, the engine only has to verify that the other moves are valued less than 0.40 and this can prove that the candidate best move is actually best without figuring out the actual value of the best move, nor the exact principal variation.

In the example, to prove that the best move is valued more than +0.40, at some point of the principal variation some second best move from the side to move can be sufficient to prove that the variation is better than +0.40, so the principal variation will contain that second best move, and the absolute best move for that position does not need to be determined.

See below for a more clear example of this.

My questions are:

1) Do you think I understand the reasons for the sentence "The principal variation is almost always wrong", or is there some other important reason that I am missing?

2) When analyzing my games with Stockfish or another popular engine, is there a way to turn off the optimizations I discussed above, and force the engine to compute the actual precise value of the best move, and a precise principal variation?

EDIT

Let me give a concrete example, otherwise what I wrote above is not so clear. This new example is super simplified, just to show the principle. Consider this case:

```
[FEN "1k3r2/pp6/3p4/8/8/n5B1/5PPP/5RK1 w - - 0 1"]

1.Bxd6+ Kc8 2.Bxa3

```

Here it is clear that the best move is 1.Bxd6+, since no other move wins a piece. Assume the engine suspects from previous analysis that 1.Bxd6+ is the only move that wins a piece. It analyses 1.Bxd6+ with an aspiration window in the interval from +1.00 to +2.00, asking for the exact value of the moves if it lies in the interval, or a cutoff it the moves wins at least two pawns. After every possible Black's reply (1...Ka8, 1...Kc8) it tries the move 2.Bxa3 first, evaluates it at +4.00, goes out of the window and returns this cutoff (without any need to try 2.Bxf8 at all). At the end, the engine happily concludes that 1.Bxd6+ is worth at least +4.00. Then the engine tries the other possible first moves by White, does not find anything worth so much, and correctly concludes that 1.Bxd6+ is the best move by White. But it returns an incorrect evaluation of +4.00 and an incorrect Principal Variation 1.Bxd6+ Kc8 2.Bxa3. The program never needed to find the exact evaluation to find the best move.

The thing I would like to write in my annotations is, instead, that this move has an evaluation of +6.00, with Principal Variation 1.Bxd6+ Kc8 2.Bxf8

So the fact that the engine is optimized only to find the best move, gives problems if I want to use it for analysis. And the mistake can be big.

I know that this example will not manage to confuse Stockfish, it was just an illustration, but I think this kind of problems can really happen, and probably this is what the blog post mentioned above wanted to say.

# Answer
It is difficult to say anything about it without reading the blog post.

Regarding your thoughts:

Evaluations of +0.2, +0.26, +0.32 are for all practical purposes the same and basically mean that the position is equal. If you use another engine you will very likely find different numbers around zero.

Computer engines are not good for deciding on one opening variation over another, since in practical play there are more important factors than what the computer thinks is a centipawn advantage.

Above all, for practical play you want to pick a variation that you are *comfortable playing*. Also in many cases you want to avoid variations where you are forced to make 20 precise moves in a row (or be lost otherwise) while your opponent has a large margin for potential errors. Depending on the tournament situation sometimes you might also pick more drawish lines over risky double-edged lines.

So, all in all, using a computer engine for opening preparation in the way you suggest does not make much sense. It is better to use a database of human games, which will tell you how successful humans are in various variations, how risky (draws vs. decided games) it is, etc.

A computer engine is still useful for checking how to punish non-theory moves or for finding novelties (typically only done by top players).
> 3 votes

# Answer
No. I **don't** think so. The point of aspiration windows to introduce better alpha-beta cutoffs.

In your example, if your search gives +4.00 **within** your aspiration window that would be the best evaluation from your engine.

> concludes that 1.Bxd6+ is worth at least +4.00.

No. +4.00 **is** the score, there is no such thing as "worth at least".

We only talk about "at least" when the score is **outside** the window. In this case, you'd have to do a new search with a wider window. Aspiration windows doesn't make your score less reliable, it makes the search quicker by introducing more cutoffs.

1. Principal variation is the moves that the engine considered the best. Of course, it's not the only way to play a position. To me, "The principal variation is almost always wrong" is not making any sense. There're many ways to play chess.
2. You shouldn't because aspiration windows is not causing you any problem. But if you insist, you could disable the aspiration margin in the source code, and then recompile from source.

Do you get the point? If you fail at your aspiration window, you'd have to do a new search. Otherwise, everything works. Please discard the "principal variation is always wrong" theory.
> 2 votes

---
Tags: engines, analysis
---


# Question
Title: Do chess engines really prune more than 90% of branches?
I was looking at Fritz Online (https://fritz.chessbase.com/) engine's parameters/performance. Here is screen relating to one of made moves.

It means that there was a general depth equals to 15 but some branches were even explored to depth 39. Engine was analysing at average speed 530k positions per second. It lasted 5 sec. so ~2.6M nodes were evaluated.

Let's consider branching factor 3 at each level. Then there are 3^15=14M leaves to evaluate (not taking into account internal nodes). As we see in case of branching factor 3 we have more nodes to analyze (14M) than it really took place (2.6M) (not even considering branches explored deeper than 15).

Branching factor in chess is aproximately 35. I'm aware there are many, many sophisticated techniques to prune branches in search tree. But really from 35 to less than 3? How it's possible that more than 90% of branches are pruned?

Two remarks:

1. Provided parameters/performance come from phase between opening and middlegame. This is NOT taken from ending where branching factor is significantly lower.
2. Depth 15 is not something unusual. In most cases program performed analysis to depth between 13 and 16 in couple of seconds.

# Answer
> 4 votes
Yes. Chess engines prune moves quite extensively. Chess programming is all about pruning.

When an engine says "search up to depth 15", it really mean depth as in iterative deepening depth-first search. It **doesn't** mean that the engine attempts to search everything up to depth 15. No good chess engine would search everything to depth 15.

It's complicated, but most of the bad moves should be reduced by depth (or even eliminated), and some critical lines variations extended beyond depth 15.

90% pruning is not uncommon, in fact it'd be more like 99.999999999999999999% according to your definition.

---
Tags: engines, depth
---


title: Five Knights Problem

text:
# Question
Title: Five Knights Problem
Many years ago, I was shown a problem involving three white pawns promoting to knights and ending up with a ring of five knights encircling the mated king. Does anybody know the starting position?

A few more thoughts:
(1) I think it was mate in seven.

(2) Unusually, every white move is forced because there is a mate threat from black.

(3) Unless I have the memory of the board upside down, the black king starts in the middle of the board and ends up on his sixth or even seventh rank surrounded by two pairs of white knights protecting each other and the fifth one executing the mate.

(4) The white king is somewhere really odd like h7 and the black mate threat comes from a minor piece - a bishop, perhaps?

# Answer
> 13 votes
In one of my books I found this "uncredited" problem, it is probably not the problem you are referring to but I thought you may find it interesting, hope you like it.

2018 Update, thanks to user @Evargalo for adding some light about the author, we can know it was composed by Gijs van Breukelen.

```
8/3P3k/n2K3p/2p3n1/1b4N1/2p1p1P1/8/3B4 w - - 0 1

1. Nf6+ Kg7 2. Nh5+ Kg6 3. Bc2+ Kxh5 4. d8=Q Nf7+ 5. Ke6 Nxd8+ 6. Kf5 e2 7.Be4 e1=N 8. Bd5 c2 9. Bc4 c1=N 10. Bb5 Nc7 11. Ba4 Ne2 12. Bd1 Nf3 13. Bxe2

```

White, with material inferiority, must act energically:

**`1.Nf6+ Kg7`** if 1...Kg6 2.Bc2+! Kg7 3.Nh5+ Kf7 4.d8=Q and black has lost the possibility of check on f7.

**`2.Nh5+ Kg6`** The black King cannot go to the last rank, d7 will crown with check.

**`3.Bc2+ Kxh5 4. d8=Q Nf7+ 5. Ke6 Nxd8+ 6. Kf5`** This is the first part of the study: White has accomplished to place the black king in a mate position. In the next set of moves each defensive move by black will be forced.

**`6...e2 7.Be4!`** Threat on f3 the only move to prevent checkmate is a sub-promotion.

**`7...e1=N 8.Bd5!!`** Threats 9.Bc4 10.Be2#

**`8...c2 9.Bc4 c1=N! 10.Bb5!`** With the idea of checkmate on e8

**`10...Nc7 11.Ba4!`** and 4 Knights cannot prevent checkmate

**`11...Ne2 12.Bd1 Nf3 13.Bxe2`** followed by 14.Bxf3#

# Answer
> 11 votes
You must be thinking of this classic Korolkov study (I-II Prize "64" 1937, according to Chernev's *Chessboard Magic!*; P1288537 in PDB). It's not a problem, nor in 7 moves, but seems to match the rest closely:

```
[Title "White to play and win (Korolkov 1937)"]
[Fen "4N3/2PP2P1/6b2/2bN2R1/6pk/p7/K1pn4/8 w - - 0 0"]

1.Rh5+ Kxh5 2.Nf4+ Kh6 3.g8=N+ Kh7 4.Ngf6+ Kh6 5.Nxg4+ Kh7 6.Nef6+ Kg7 7.Ne6+ Kf7 8.d8=N+ Ke7 9.c8=N#

```

In the starting diagram Black threatens mate with, appropriately, a checking Knight promotion: c1N+ and either Ndb3# or Bd4+ and mate. If Black diverges from the main line then White usually promotes a Queen with check; exceptions are 1...Kg3 2.Rh1 and 4...Kh8 5.Nxg6#.

It is possible that youur friend showed you the problem without the first two moves, thus making you think that it was a mate in 7.

# Answer
> 3 votes
I don't know about 5 knights, but it has been shown that 3 knights and a king can force mate.

The method is given in Reuben Fine's Basic Chess Endings, ISBN 0-679-14002-6, my copy of which seems to have disappeared, along with the memory of its contents in this instance. I do however, distinctly remember that this endgame situation is covered in the book.

---
Tags: knights
---


# Question
Title: Beautiful retrograde analysis problem by Alexsey A. Troitsky
I saw this beautiful, subtle & accessible problem a couple of days ago, and wanted to share it with you folks. (It's by the ground-breaking endgame theorist who e.g. invented the "Troitsky line" in KNNvKP analysis.)

```
[title "A.A.Troitsky - Bohemia 1910"]
[fen "1B6/bp3ppp/BR1pPp2/RPp1kP2/bpK5/3P2P1/1PP3PN/5nrr w - - 0 1"]

```

White to play and mate in 2?

The forward play is pretty obvious. But, as is common in retrograde analysis, you need to justify the forward play by figuring out what was Black's last move.

Even if/when a speedybrain supplies a full answer, I hope that you can still enjoy solving the puzzle.

# Answer
> 7 votes
Short answer: last move was -1. c7-c5, and before that -1...Rc6-b6, the white bishop returns to c1 and -d2-d3 unlocks the cage, enabling -Kd3-c4 and everything unlocks. -1. c6-c5 doesn't work because the white bishop will definitely end up trapped behind the black bishop in the northern dark squares and can't get out - -c6-c7 will leave the two bishops on d8/e7/f8 and not a7/b8 because of tempo concerns (retro-opposition), and they can't leave.

(Notice the use of minus signs, white moves noted with ..., and I said the white bishop "returns" to c1 - I'm *retracting* moves from the diagram position, which makes this kind of problem much easier.)

---

Long answer: Now how to explain this without fluff or skipping too many "obvious" details? From a pedagogical point of view, I will insist on talking about this problem using ***retractions*** rather than the usual forward chess moves; it's easier and far clearer to play moves *backwards from the diagram* than it is to create some arbitrary position, assert that it's legal then play forward moves to reach the diagram. It also ensures we don't miss anything - easier to check every possible retraction from the diagram than to check that every possible chess position leading to the diagram has ends with a certain move.

Those who already understand retraction can probably see the cage themselves, skip the first two bolded points and jump right to the section -1. c7-c5.

**Pawn captures, basics of retraction explained**

Standard approach is to look at pawn structure. Each side has 14 units and 8 pawns. White's captures were hxg3 and axb, black's were exf6 and axb. So from the diagram, we can't magically retract (take back) an uncapture immediately.

Also, the fact that all bishops are on the board and each side has their full 8 pawns means we can't retract exf6, d7-d6 or ...d2-d3 without the corresponding bishop being at home. (In the forward direction, it means that the pawn move was played while the bishop was at home and hadn't yet moved.)

A side can retract themselves into check but the other side must retract immediately to remove the check (once again this is seen in reverse - in the forward direction, one side checks and the king moves away.) For instance -1. c6-c5 Kb3-c4 would be possible, except that black can't remove the check from Ba4. -1. Kf4-e5 is impossible as white needs to retract -1...hxg3 to answer (pawn structure.) -1. Ne3 is impossible as one cannot deliver check by retracting (in the forward direction, that would be black moving away from check.)

**What is a retrocage?**

Usually, once all pieces have enough freedom of retraction, the position shouldn't pose any legality problems. We therefore want to retract moves with the goal of freeing as many pieces as possible. By considering all retractions (it's not hard once you're used to it, like seeing legal chess moves), we notice a few things:

* The kings can't retract at the moment.
* The southeast (bottom-right) corner unlocks with retracting a knight move, impossible for now because of the kings.
* The west (left) side, specifically the 8 pieces in a rectangle except bBa7 and wRb6, is a cage that unlocks only with -Bb3-a4, which is again impossible because of the kings.

So to unlock the position, we need to free the kings by giving them a retraction. So a bishop has to go home to c8, f8 or c1 to enable a pawn retraction to (respectively) d7, e7 or d2. The black light bishop is trapped on a4, so that leaves just the two dark bishops.

**Position is legal: -1. c7-c5**

We retract for example -1. c7-c5 Rc6-b6 -2. Be3-a7 Bb8-a7 -3. Bh6-e3 Be3-a7 -4. Bg5-h6 Bc1-e3 -5. Bh6-g5 d2-d3 (the white dark bishop came home) -6. Bg5-h6 Kd3-c4 and the cage unlocks. The white king moving frees everything, as explained above.

**En passant is legal: -1. c6-c5? is impossible**

The crux of the matter. If we try to retract this, then the two dark bishops are locked in step on the 6 dark squares in the north. They can't pass each other, nor can they lose a tempo since there are no other legal retractions except -c7-c6, which incidentally commits the bishops to the dark squares to the left or right of c7. There are only 3 cases:

1. Both bishops on the left (bBa7/wBb8). This is impossible - the bishops can't lose tempo, and with the bishops in such a position (i.e. right now, the only chance) it's white to retract, not black.
2. Both bishops on the right (bBd8/wBf8). Once -c7-c6 is retracted, the bishops are trapped in these squares. The only way to let them out is to retract e7xf6 (impossible; the black bishop can't find itself on the right of the white one to be at home on f8), or to retract -d7-d6 (also impossible; the black light bishop on a4 can't come home before the cage is unlocked.)
3. Black bishop on the left, white bishop on the right. The same problem as in (2), we can't get either bishop home as they're each trapped on the wrong side of the pawn wall.

With no other way to unlock the position, we conclude that -1. c6-c5 is impossible.

**Conclusion:** Therefore -1. c7-c5 was the last move (no other possibilities), so en passant is provably legal and forward mate is 1. bxc6 e.p.+ Bb5 2. Raxb5#.

# Answer
> 5 votes
Pawn still being `d2` allows us to complete the answer: `c7-c5` must have been Black's move. Please see the added discussions below.

*Some initial thoughts:*

To get started, by a trivial process of elimination we can boil the choices down to only two black candidate moves: `c6-c5` or `c7-c5.` Now we have to resolve the dilemma by stepping further back and figuring out what aspect of the position allows to distinguish between the two. It seems to me that the **main twist lies in how the queen-side came to be**, that is: which events and in which order took place for the two rooks to end up on `b6` and `a5`, the bishop on `a4` and the two pawns on `b4` and `b5.` Some initial observations:

1. It seems the only route for the king to get to `c4` is via `c3`, which puts a constraint on when `axb4` took place.
2. Moreover, `Kc4` must have been played after `Ba4,` as otherwise, if the king is on `c4` the bishop can never reach `a4.`
3. Easier points: `Ra5` is played after `axb4` (not to say immediately after), `Ba6` is played before `axb5` (because the capture closes all paths to `a6`) and `Ba4` is played once `axb5` has taken place.
4. Point 2 suggests that the king must have the square `c3` available in order for the bishop to reach `a4`. This would imply that `axb5` capture happens first, the bishop gets to `a4` then `axb4` takes place.
5. If 4 is true, then how the heck can the rook get to `a5?` :) If we can't resolve this, i.e., find a sequence of events that allow the above points together with the rook reaching `a5,` then point 4 contains a mistake/contradiction.
6. Slightly different consideration would be: to assume the white bishop is for the moment on `d7` for instance, so neither captures on `b4` and `b5` have taken place yet. The white rooks are on `a6` and `b6,` (that they've reached e.g. via `f4-c4-a6/b6`) and the black knight (to be captured on `b5`) is on `c7`. We consider `axb4` to happen first (assume it captures a white knight): then the rook gets to `a5,` the bishop goes to `a6` via `d7-b5,` then the knight goes to `b5` which leads to `axb5` which in turn frees `a4` for the black bishop, so `Ba4` takes place. Everything seems fine at first glance, but in all of that, how the heck will the white king reach `c4?` :)

**Quick recap:** according to point 5., we cannot resolve how the rook gets to `a5`, whereas if we follow point 6., the rook problem is resolved but we cannot(?) account for how the king reaches `c4` eventually. I believe if we can solve this dilemma of the queen-side, the distinction between whether `c6-c5` or `c7-c5` is correct will follow immediately.

---

*A follow-up to complete the answer*

A possibility that resolves the aforementioned queen-side problem:

Point 6 would actually work if white king had the `d3` square available in order to allow the black bishop to get to `a4`. More precisely, these are the sequence of events:

7. We are considering the case `axb4` happens before `axb5,` the rooks are on `a6` and `b6,` the white bishop is on `d7`, the white pawn is still on `d2` so the king sits on `d3.`
8. 7 implies that `c1` bishop is still locked in and gets to reach `b8` very late. `axb4` frees `a5` for the rook, so `Ra5` takes place immediately after. Then `d7` bishops returns to `a6` via `b5` after which `axb5` happens (for instance capturing a knight, which could without any loss of generality have come from `c7` to `b5`). After `axb5,` the black light square bishop gets to `a4`, e.g., via `b3` directly. Now the king can hop to `c4,` allowing `d2-d3.`
9. Now comes another crucial step: in the previous points we've assumed the black bishop is just sitting on `a7,` that means that if the `c1` bishop is to ever reach `b8,` the `a7` bishop must be able to move freely along the `a7-f2` diagonal, which in turn implies the black `c` pawn cannot be on `c6` as that would not only impede the rook from moving and freeing the `a7` bishop's diagonal but also trap the white bishop on `b5` or `d7`. Thus, the pawn must be on `c7`, which allows `Rc6` and the aforementioned bishop maneuver, followed by a simple sequence (after `kc4` and `d2-d3`) to get the two bishop to `a7` and `b8,` e.g., black bishop to `d4` and then `c3` to let the white bishop to pass first, i.e., white bishop to `e3-a7-b8`, then the black bishop returns to `a7`, the rook on `c6` returns to `b6` and black plays `c7-c5.` Summary of that last dance of bishops: `1. Rc6 Bd4 2. Be3 Bc3 3. Ba7 Bd4 4. Bb8 Ba7 5. Rb6 c7-c5`. It must be noted that the pawn still being on `d2` does not interfere with the occurrence of any of the other events other than that of the dark squared bishops, which has been already resolved. Thus, it can safely be considered without leading to contradictions.
10. In short, previous attempt in point 4 and 5 was deemed to be impossible as the rook on `a5` could never be accounted for in those variations. Instead following up on the approach in point 6 in conjunction with the idea of the pawn still being on `d2` before the exchanges on `b4` and `b5` have taken place and naturally in turn the moves `Ra5` and `Ba4,` we seem to have found the only way the current queen-side situation could be reached, which required the black `c` pawn to be still on `c7` throughout.

# Answer
> 1 votes
Nice.

> Black has 8 pawns, so his bishops are original, so Black hasn't just played d6 or exf6. If Black has just moved a piece, it must've moved from a square where it was already checking; this is impossible. So Black has just moved the pawn now on c5. Why not c6-c5? The problem is that White can't give Black a penultimate move; wNh2 can't retract to retro-release bRh1 because wN would move from a square where it was checking. Black is missing only 2 units, so White played axb & h2xg3, so may not retract f2xg3. Bc7-b8 doesn't relieve Black's retrostalemate. White's only way to give Black a penultimate move is retro -1 ... c7-c5 -2 Rc6-b6 retro-releasing bBa7.

Except that

> with a black pawn on c7, the pawns on c7, d6, f6 and g7 lock the bBa7 out and prevent it retracting to f8. So before bBa7 can retract to f8, bPd6 must retract to d7. This entails retracting bBa4 to c8. This entails moving wK. Seeing as wPd3 can't go back until wBb8 is home on c1, moving wK entails moving bK, which entails retracting f4-f5. So retro -1 ... c7-c5 -2 f4-f5 Kf5-e5 -3 Kd4-c4 Bb3-a4 and now bBb3 and bPd6 can go home, wRb6 can retract to c6, bBa7 can go home to f8 and finally it unravels.

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Tags: problems, retrograde-analysis
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# Question
Title: What service can be used to save and replay/analyze a chess match?
I've been starting to write down my chess matches in a scorebook, but would like to find a site where I can transcribe the match and then replay move by move by game to help me analyze what I did well and where I made mistakes.

I remember accidentally finding this kind of a SAAS a while ago, but I never bookmarked it, and don't even know what to search for anymore.

Can anyone give me some pointers what to search for, or recommend a site that can provide this kind of service?

# Answer
For an online tool, lichess is good. You can enter your game and have it analysed by a computer engine.

The analysed game will have annotations in plain language ("mistake/blunder/inaccuracy") and of course contain the computer evaluation score after each move.

Once you have a game analysed on lichess, they have another good feature called: "Learn from your mistakes". Here it will ask you at every mistake/blunder to find a better move.

Another feature which might help you is called "chess insights", basically statistics of your games (e.g. which opening did you score best, etc).

You can do much the same (and more) offline using a chess database software. Scid is a popular free one, chessbase a popular non-free one. However as a beginner you might find the lichess features sufficient and more easy to use. In any case you can import/export between lichess and chess databases.

Particularly for a beginner it is difficult to properly analyze a game. Computers will tell you about tactical mistakes, but finding problems in strategy/positional play using computers will be just about impossible on your own. Therefore I would suggest to find a stronger player look over your games and give you tips. Ideally you'd join a chess club, but if that's not an option you could also post your games in online forums.

Another way to improve is to read or watch commented games, particularly those in the openings you play.
> 7 votes

# Answer
Lichess.org allows (free) registered players to upload games and have stockfish analyse them. The site lets you adjust what score difference the computer will consider an inaccuracy, mistake, and error.

Many (almost all) chess forums allow you to post a game and ask the other players to comment on the games.
> 6 votes

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Tags: analysis, notation
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title: Automated annotation of good moves

text:
# Question
Title: Automated annotation of good moves
It is easy enough to use a chess engine to "annotate" a game to the extent of pointing out mistakes and blunders: when the evaluation function drops by greater than a certain amount, the move is deemed bad enough to merit a "?" or a "??".

Has anyone tried to develop a program to add exclamation marks to good/brilliant moves? In the eyes of a chess engine, those moves would usually be the best move for the position, but just being the best move does not make a move brilliant, because the best move may be obvious. Exclamation marks are added to moves that are hard to find by humans, which is somewhat subjective. But I imagine one could come up with some rules or heuristics, at least for things such as recognizing sound sacrifices. Or maybe there is a way to train the system using a library of annotated games.

I wouldn't expect such a tool to be better than a good human annotator, but I find the question interesting from an artificial intelligence perspective.

# Answer
> 3 votes
Chesstempo has this function now.

Ref: https://beta.chesstempo.com/blog/9/good-move-annotations

# Answer
> 3 votes
It is not an answer, but an extended comment.

A great question, and a very interesting functionality proposal.

I don't know if such a tool exists - however if I were to implement it I'd consider analysing the same position using different strength settings. For example, if the move is only found by the top strength, it is a good candidate for `!!`. It is more or less easy to implement, but may require some effort tuning up.

# Answer
> 1 votes
Lichess has an excellent import tool with computer aided analysis.

After uploading a game and analyzing with Stockfish, you can download an annotated PGN of the game. It adds alternate lines and annotated symbols (?! for inaccuracy, ?? for blunder, etc.)

In the PGN, move 23. Qf3 looks like: `23. Qf3?? { (3.13 → 0.10) Blunder. Best move was Qg4. }`

Here's an example game I uploaded and analyzed. Use the tabs/links below the game "FEN & PGN" \> "Download Annotated" to export the annotated PGN.

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Tags: annotation
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