# Question
Title: HalfKP Structure for Stockfish / Shogi NNUE - how does it work?
Stockfish now uses a neural network for position evaluation. The structure of this neural network was introduced for Shogi by Yu Nasu in the paper dubbed "Efficiently updatable neural network - NNUE". Unfortunately it is in Japanese.

It is a fully connected neural network with four layers. The first layer receives an encoded chess position. The second and third are hidden layers and then there is final output layer that gives the evaluation.

The input layer receives a chess position encoded as a "HalfKP" structure, and this is where I am completely lost. A picture is available here.

The encoding seems to work like this. Suppose we have the starting position. We first consider only the white pieces. We encode the position by always considering the position of the white king together with a white non-king piece for each square. The resulting value is then either '1' or '0'.

Consider the starting position. We have

```
King on a1, Pawn on a1 -> 0
King on a1, Pawn on a2 -> 0
...
King on e1, Pawn on a2 -> 1
...
King on e1, Pawn on e2 -> 1
...

```

and so on. This input is fully connected to the next layer. Then we do the same for the black pieces.

Question 1.) Is my understanding correct?

Suppose we have the move `e2e4`. There are only two inputs which change:

* `King on e1, Pawn on e2` changes from 1 to 0
* `King on e1, Pawn on e4` changes from 0 to 1

There is apparently some efficiency gain here claimed in the original paper, but I do not see where. After all, the two nodes above are connected to *every* node in the second layer, so we have to update *all* second layer nodes.

Question 2.) Why is this efficient?

An encoding that would be much more straight-forward would be to simply use bits to indicate positions of the pieces, similar to bitboards.

```
King on a1 -> 0
...
King on e1 -> 1
...
Pawn on e2 -> 1
Pawn on e4 -> 0

```

If we use such an input encoding, we have less input nodes. Also updating for the move `e2e4` just changes two input nodes. Such input seems to be common in other approaches, like AlphaZero and Lc0.

Question 3.) Why does one not use such a much easier encoding? Why do we use combinations of King + Piece? What do we gain here?

Question 4.) The first layer uses 16 bit integers, the next layers 8 bit integers. What is the reason for this choice? Obviously we need to limit the range to operate with fixed-point arithmetic due to memory constraints, but why 16 and 8, and not 16 and 16, or 32bit and 32bit?

The first half of the input layer (for white) is fully connected to the first 256 nodes of the second layer; the second half of the input (for black) is fully connected to the latter 256 nodes of the second layer.

Question 5.) Why do we consider the white and black pieces separately? What is the benefit? What is the so-called (full) `KP`, and what is the relation to `HalfKP`?

Question 6.) Is it possible to illustrate the update and efficiency gain with the above `e2e4` example?

# Answer
> 8 votes
**\[1\]** Your understanding is correct, with one slight adjustment. Instead of thinking about it as "King on a1, Pawn on a2", you should think of it as two things: "King on a1, Friendly Pawn on a2", and "King on a1, Enemy Pawn on a2". The input layer knows the colors of the pieces. Note that I do not say White/Black, but Friendly/Enemy, which are relative. This is because the weights are the same for both sides, but flipped around and rotated a bit (depends on the engine)

**\[2\]** Suppose we have a full board. All 32 pieces on the board. To compute the first layer of neurons (but not apply an activation), we will in essence perform 30 (we don't care about the king's directly) vector additions. You pointed out rightly that the inputs are 0s and 1s, so we use addition and not multiplication.

I now take a record of the values in each neuron (before activation). Now you make the move e2e4. You correctly point out that (for each side) two things change. Turn one bit off (King on X, Friendly Pawn on E2) and turn on (King on X, Friendly Pawn on E4). To update the remembered neurons, we only need to take the original values, subtract a vector of E2 pawn weights, and add a vector of E4 pawn weights. 31 additions (operations) now becomes 2.

**\[3\]** As to your comments about using a simple input system. Your example is 768(=6x2x64) input bits. "Is piece A of colour B on square C". This works just fine. There is a chess engine named Halogen using this scheme, and I've trained networks for it. It is strong, but not as strong as the halfkp style networks. The theory is that the overspecialization allows for more knowledge, but without additional computation cost.

**\[4\]** This one is a technical question, and it (in my view) relates to the first comment where the inputs are 0s and 1s, so really we use addition and not multiplication. Suppose you have two numbers, both of which are stored in 8-bits. If you multiply them, the result will need upto 16-bits to be represented.

Now consider the later layers of the network (ignoring the input for now). You take an 8-bit input, multiply by an 8-bit weight, sum a whole bunch of these up, and then output an 8-bit weight. In the intermediate steps you are dealing with 16-bit types, but later that information is packed down into 8-bits.

Multiple times I typed (before the activation) in my earlier answers. This is important. The intermediate data for computing the next layer of neurons is 16-bits. And since we are constantly adding and subtracting little pieces (from your e2e4 move), we are dealing with the intermediate data, and thus we want it available in 16 bits. For technical reasons, you might as well use 16-bits for the input weights, even though they are actually going to be within an 8-bit range. This is all subjective, and you or anyone else could use another scheme and be fine.

**\[5\]** HalfKP allows us to reuse the same weights for both sides. Some engines will flip, some will rotate. For example, the weight for (White King on A1, White Pawn on A2) will be the same as the weight for (Black King on H1, Black Pawn on H2). This makes training much easier, as it "halves" the number of weights to be trained, which is akin to having more data.

Other solutions like HalfKA (accounts for the enemy King) are also viable, and are being used in an engine named Seer. The halfkp paradigm has some other ramifications to something called I call factorizorss, during training, but that is a much more complex discussion.

**\[6\]** I'm not one for making big graphics, but I suppose "Yes" does answer your question :)

Source: I programmed all of this at one point https://github.com/AndyGrant/EtherealDev/tree/openbench\_nnue/src/nnue which involved me going through each of your questions. I happen to have a different setup than Stockfish, but I considered the same issues and came to my own solutions while understanding the alternatives.

---
Tags: software, stockfish, programming, shogi
---


# Question
Title: Does the new Netflix series "The Queen's Gambit" resemble any real life chess master?
Recently, a Netflix series has been launched entitled **The Queen's Gambit** which surely created a lot of hype in the chess community. Does the protagonist Beth Harmon resemble anyone (fully or partially) in real life? This is although the makers of the series said the character is fictional. Sill, I am kind of sceptic about this.

# Answer
The character Beth Harmon is purely fictional. The series is based off a book by the same title by Walter Tevis. The author had a tendencie to base books drawing from personal experiences but he wasn't a chess prodigy that's for sure. He was however a good club level player which is why the book has such strong chess knowledge. In that time period, there are no valid players that could fit as inspiration for the character (that I can place at least). The chess advisors in the show were Bruce Pandolfini and Garry Kasparov which really shows the high-calibre efforts the production team went to to get the show's chess moments bang on.

EDIT: Found the following article https://www.radiotimes.com/news/on-demand/2020-10-29/the-queens-gambit-book-netflix/

> Tevis previously told The Times that the character was created as a “tribute to brainy women” adding that “I like Beth for her bravery and intelligence. In the past, many women have had to hide their brains, but not today,” he said.
>
> He listed his daughter and his aunt – who had gifted him with his first chess set – among the women who had inspired the character.

Regarding the games however that is a different story; Most the games are based on famous games. The final game in the series where she beats Borgov is based off a game between Vassily Ivanchuk and Patrick Wolff at the Biel Interzonal in 1993 for example. An absolute monster of a game to watch though;

Those researching the film did a fantastic job in finding great games to base their games on. Specifically move *38 Ne6* which is a more direct and simplified line.

**The Movie Game (Simplified Ivanchuk v Wolff)** The movie is a simplified and more modern line than the game it was based on.

```
[FEN ""]
[Event "?"]
[Site "?"]
[Date "2020.08.24"]
[Round "?"]
[White "Harmon"]
[Black "Borgov"]
[Result "1-0"]
[ECO "D20"]
[PlyCount "105"]
[SourceVersionDate "2020.10.31"]

1. d4 d5 2. c4 dxc4 3. e4 Nc6 4. Be3 Nf6 5. Nc3 e5 6. d5 Ne7 7. Bxc4 Ng6 8. f3 Bd6 9. Qd2 Bd7 10. Nge2 a6 11. Bb3 b5 12. a4 O-O 13. O-O Qe7 14. Rac1 Nh5 15. g3 h6 16. Bc2 Rab8 17. axb5 axb5 18. Ra1 Ra8 19. Bd3 Bb4 20. Rxa8 Rxa8 21. Qc2 Bc5 22. Nd1 Bd6 23. Nf2 Nhf4 24. Rc1 Qg5 25. Kh1 Qh5 26. Ng1 Nxd3 27. Nxd3 f5 28. Nc5 Bc8 29. Rf1 Ne7 30. Qd3 fxe4 31. fxe4 Qg6 32. Kg2 Kh7 33. Nf3 Ng8 34. Nh4 Qg4 35. Nf5 Nf6 36. h3 Qg6 37. Ne6 Ra4 38. b3 Rxe4 39. Nxd6 Bxe6 40. dxe6 cxd6 41. e7 d5 42. Bc5 Qe8 43. Qf3 Qc6 44. b4 Qe8 45. Qf5+ Kh8 46. Qxf6 gxf6 47. Rxf6 Qh5 48. Rf8+ Kg7 49. e8=Q Re2+ 50. Kf1 Qxh3+ 51. Kxe2 Qg2+ 52. Rf2 Qe4+ 53. Kd2 1-0

```

**The Game that its based off**

```
[FEN ""]
[Event "Biel Interzonal"]
[Site "Biel"]
[Date "1993.??.??"]
[Round "1"]
[White "Ivanchuk, Vassily"]
[Black "Wolff, Patrick G"]
[Result "1/2-1/2"]
[ECO "D20"]
[WhiteElo "2705"]
[BlackElo "2585"]
[PlyCount "144"]
[EventDate "1993.07.??"]
[EventType "swiss"]
[EventRounds "13"]

1. d4 d5 2. c4 dxc4 3. e4 Nc6 4. Be3 Nf6 5. Nc3 e5 6. d5 Ne7 7. Bxc4 Ng6 8. f3 Bd6 9. Qd2 Bd7 10. Nge2 a6 11. Bb3 b5 12. a4 O-O 13. O-O Qe7 14. Rac1 Nh5 15. g3 h6 16. Bc2 Rab8 17. axb5 axb5 18. Ra1 Ra8 19. Bd3 Bb4 20. Rxa8 Rxa8 21. Qc2 Bc5 22. Nd1 Bd6 23. Nf2 Nhf4 24. Rc1 Qg5 25. Kh1 Qh5 26. Ng1 Nxd3 27. Nxd3 f5 28. Nc5 Bc8 29. Rf1 Ne7 30. Qd3 fxe4 31. fxe4 Qg6 32. Kg2 Kh7 33. Nf3 Ng8 34. Nh4 Qg4 35. Nf5 Nf6 36. h3 Qg6 37. g4 Bxc5 38. Bxc5 Ra4 39. Rf3 Rc4 40. Be7 Bxf5 41. Rxf5 Rd4 42. Qe3 Rxe4 43. Qf3 Rf4 44. Rxf4 exf4 45. Bxf6 Qxf6 46. Qd3+ Qg6 47. Qe2 c6 48. Kf3 cxd5 49. Kxf4 Qf6+ 50. Kg3 Qd6+ 51. Kf3 b4 52. h4 Qf6+ 53. Kg3 Qd6+ 54. Kf3 Qf6+ 55. Kg3 g6 56. Qe8 Qd6+ 57. Kf3 Kg7 58. g5 hxg5 59. hxg5 d4 60. Qe4 d3 61. Qb7+ Kf8 62. Qc8+ Ke7 63. Qb7+ Ke6 64. Qe4+ Kd7 65. Qb7+ Kd8 66. Qa8+ Kc7 67. Qa7+ Kc8 68. Qa8+ Kc7 69. Qa7+ Kc6 70. Qa6+ Kc5 71. Qxd6+ Kxd6 72. Ke3 Ke5 1/2-1/2

```

I believe the Kentucky game to be based of Nezhmetdinov vs Kasparian game as well.

```
[FEN ""]
[Event "Spartak Team Ch (1955), Riga LAT"]
[Site "?"]
[Date "1955"]
[Round "?"]
[White "Rashid Gibiatovich Nezhmetdino"]
[Black "Genrikh Kasparian"]
[Result "*"]
[ECO "B11"]
[PlyCount "93"]

1. e4 c6 2. Nf3 d5 3. Nc3 Bg4 4. h3 Bxf3 5. Qxf3 e6 6. g3 g6 7. Bg2 Bg7 8. O-O Nd7 9. Qe2 d4 10. Nb1 e5 11. d3 Ne7 12. f4 Qc7 13. a4 O-O 14. f5 f6 15. Nd2 Bh6 16. Kh2 Kh8 17. fxg6 hxg6 18. Nf3 Bxc1 19. Raxc1 Nc5 20. c3 Nb3 21. Rcd1 Rad8 22. Nh4 Qc8 23. Bf3 Qe6 24. Bg4 Qf7 25. Nf3 Qg8 26. h4 Kg7 27. Rf2 Rd6 28. Rdf1 Rdd8 29. Qc2 b6 30. h5 c5 31. hxg6 dxc3 32. bxc3 c4 33. d4 exd4 34. cxd4 Nxd4 35. Nxd4 Rxd4 36. e5 f5 37. Bxf5 Qd5 38. Be6 Rh8+ 39. Bh3 Nxg6 40. Rf7+ Kh6 41. Qxg6+ Kxg6 42. R1f6+ Kg5 43. Rf5+ Kg6 44. R7f6+ Kh7 45. Rh5+ Kg7 46. Rg5+ Kh7 47. Bf5# *

```

*I will try to pin all the games I can find in the show so this list is likely to grow.*
> 23 votes

# Answer
I take it you're referring to Beth Harmon, the protagonist of the series. There's no single chess master that resembles her, but various masters resemble her partially:

* **In the fact that she's female**: there's only been one woman who's reached the top 10 players in the world: Judit Polgar. Two other women, Hou Yifan and Vera Menchik, come close as well.
* **In the fact that she's alcoholic and used drugs, and her health suffered for it**: see Mikhail Tal. Tal didn't use drugs, but he was a heavy drinker and smoker, and his health was poor for this reason. Tal also loved chess so much he did other extreme things, such as leaving the hospital to play in a chess tournament. Former world champion Alexander Alekhine also springs to mind, in fact it's been argued that Alekhine lost the 1935 world championship to Max Euwe because he was drinking too much during that match.
* **In the fact that she took on and defeated Soviet masters**: this clearly resembles Bobby Fischer. Fischer's career is similar in other ways, such as the ups and downs he went through, and his eccentricity.
* **In the fact that she's a prodigy**: there've been lots of chess prodigies. Some names that immediately spring to mind are Paul Morphy and Jose Raul Capablanca, both of whom defeated strong masters while still young children, and Sergey Karjakin, who at 12 years old became the youngest person ever to become a grandmaster in 2002, and held the record until 2021. Wikipedia has an article on chess prodigies with more names, as well.
> 9 votes

# Answer
Yes it correctly describes the life of a chess player. Wesley So has been adopted. The face of Alexandra Kosteniuk. Prodigy of Morphy. Life of Fischer against the Russians. Drinks of Alekhine. Beth Harmon is the combination of the lives of the greatest chess players.
> -1 votes

---
Tags: history, famous-players, fiction, film, famous-events
---


# Question
Title: Does taking tranquilizers count as cheating in chess?
In the second episode of *The Queen's Gambit*, from Wikipedia's summary:

> After her overdose, Beth is forbidden to play chess. Time passes and Beth is adopted as a teenager by suburban couple Alma and Allston Wheatley. Allston is emotionally distant and frequently leaves for "business trips"; it soon becomes clear that their marriage is not a happy one. At her new high school, Beth is bullied by the popular girls from the "Apple Pi Club" for her drab clothes. Beth discovers her adoptive mother is taking the same tranquilizer pills that she was given at the orphanage and secretly steals some for herself, allowing her to play mental chess again. She also steals a chess magazine and learns about the upcoming Kentucky State Championship. She writes to Mr. Shaibel, who sends her the money for the entrance fee. As she cruises through her games, she develops a crush on one of her opponents, a young man named Townes. After the second day of the tournament, during which her periods start, Beth comes home to find that Allston has deserted them. Beth fears that she will be sent back to the orphanage, but Alma tells her they will lie so she can stay. **During her final game of the tournament against Harry Beltik, the highest-ranked player, Beth becomes flustered and runs to the restroom, where she takes a tranquilizer pill, then wins the game.** Upon learning of the prize money on offer in a tournament in Cincinnati, Alma hatches a plan for the two women to support themselves.

(emphasis mine)

This description makes it sound like tranquilizers are a performance-enhancing drug. Does taking tranquilizers count as cheating in chess? I'm aware that there is some kind of anti-doping tests in chess, but I do not know what the tests test for.

# Answer
The *World Chess Federation (FIDE)* uses the list of prohibited substances published by the *World Anti-Doping Agency*.

I did not see tranquilizers on the list, although I can't say I'm familiar enough with the names of medications to know for sure.

Tranquilizers would seem to be a rather counterproductive way to cheat in most sports, which might explain why they're not on the list.
> 19 votes

---
Tags: rules, cheating, film
---


# Question
Title: What is 'Depth' in Lichess game analysis?
I have started analyzing my games in Lichess. I'm wondering what does `Depth` mean in the Stockfish analysis?

# Answer
It means how many half moves ahead stockfish looked from the current position. It doesn't mean it looked at all the moves possible to that extent thought, it trims what it analises, otherwise it would be unable to reach such depths, this means a mate in 10 for example may only be found when stockfish searches in greater depths. In general, greater depths mean better analysis and moves suggested by stockfish. The only limiting factor is time and processing power.
> 10 votes

# Answer
Depth counter shows the latest status of the algorithm in the search tree. Depth 10 means the algorithm checked all moves in 10 node distance. Each node is a position (each half move changes the position, so depth of 10 translates to 5 moves).

As you wait longer and longer it will get deeper thus will provide better evaluation.
> 1 votes

# Answer
Wrong answer: "Depth 10 means the algorithm checked all moves in 10 node distance."

Right answer: "It doesn't mean it looked at all the moves possible to that extent thought, it trims what it analises, otherwise it would be unable to reach such depths, this means a mate in 10 for example may only be found when stockfish searches in greater depths."

Stockfish isn't a pure brute force engine. It uses alpha-beta pruning.
> 0 votes

---
Tags: stockfish, lichess, depth
---


# Question
Title: How do endgame tablebases calculate checkmates to do retrograde analysis on?
I understand that once endgame tablebases get checkmates, they do retrograde analysis and are able to calculate forced wins. However, how do they calculate the checkmate in the first place? Do they just use brute force?

# Answer
> 4 votes
Yes, endgame tablebases are calculated by brute force. That's why we only have complete 7-men tablebases today (which were published in 2012).

When stockfish finds a mate with more pieces than stockfish has calculated until only 7 men are on the board and the tablebases give stockfish the solution for the rest.

# Answer
> 2 votes
Roughly, yes. To build a tablebase for a certain material combination you will want to have every legal configuration of those pieces in memory. (in practice one can optimize that a bit) Then you check which of the positions are already checkmate. And yes, then you work backwards and find longer and longer wins. (and then all remaining positions that aren't wins for either side are draws)

---
Tags: engines, software, tablebases
---


# Question
Title: How does competitive chess affect players' mental health?
I suppose that participation in international open tournaments has a positive mental effect on most amateur players. As for the professionals involved, if they have other sources of income and also don't suffer from untreated issues then I can't see any mental health risk. Concerning international closed tournaments, there players have already been preselected both by their coaches and the organisers, thus I assume most of them should be well-adjusted.

# Answer
> 1 votes
> if there are certain talented players who should not become competitively active cause of their mental health status

On the contrary, there are many chess players, successful and otherwise, who get relief from their mental problems by playing chess. Fischer and Bloodgood are probably at the extreme end of mental disturbance but there are many at all the levels below that.

Victor Kortchnoi, in his famous world championship match with Karpov, is another famous example at a lower level of mental disturbance.

> others who could become successful only under the supervision of a mental health practitioner

Again, I think you have it the wrong way round. Without their mental health problems many strong GMs wouldn't be that strong.

---
Tags: psychology
---


title: Why does white not play cxd4 here?

text:
# Question
Title: Why does white not play cxd4 here?
I am Black and my opponent is White. Here the computer recommends Rxd4, which I have done (the rook captured bishop here).

```
[FEN "4r1k1/1pp2pp1/p6p/4q3/P2rPn2/2P1QP1P/1P4P1/R4RK1 w - - 0 1"]

```

It's obvious then that Qxd4 is a blunder, because then I play Ne2 to fork the king and queen and the game is over. I would expect the computer to play cxd4 here to go up material, but the computer plays Rfe1.

Why not cxd4 here? What future sequence am I not seeing?

# Answer
Stockfish, at depth 20, evaluates Rfe1 with a score of -8.5, while cxd4 has one of -2.6. With so large a difference, the explanation is that you were playing against a *weak* computer. There is usually a gradient (e.g. from 1 to 10) of difficulty to choose from when playing against a computer, so you have probably chosen something far from 10. Chess.com (guessing from the screenshot) also has adaptative opponents that will grow stronger/weaker according to your performance.

For what it's worth, shortly after cxd4 White gives up a rook and a pawn for Black's knight and has an exposed king and piteous pawn structure —so Black wins anyway—, as follows.

```
4r1k1/1pp2pp1/p6p/4q3/P2rPn2/2P1QP1P/1P4P1/R4RK1 w - - 0 6

1. cxd4 Qg5 2. Kf2 Qxg2+ 3. Ke1 Qxb2 {Double threat: Qxa1+ and Ng2+ (a royal fork)} 4. Qxf4 Qxa1+ 5. Ke2 Qxd4

```
> 3 votes

---
Tags: analysis, computer-chess
---


title: Is 1...d5 ever a bad move?

text:
# Question
Title: Is 1...d5 ever a bad move?
I notice that as Black, I virtually always play d5 as my first move. It's usually in response to 1. e4 (Scandinavian Defense) or 1. d4 (Queen's Pawn Game). As a hypothetical, if I premoved 1... d5, what is the worst that could happen? Are there any openings in which it is not a strong move?

# Answer
Against `1.c4`. This will allow white to exchange their c-pawn for black d-pawn and later gain a tempo. `2. cxd5 Qxd5 3.Nc3`, or `2...Nf6` at some point will be followed with `e4` with tempo. All in all, white can take control of the center.

According to lichess' database `1.c4 d5` is very rarely played.

However, the move is probably not losing; stockfish gives it: 0.6. The significance of this advantage varies a lot depending on the player's strength.
> 22 votes

---
Tags: opening
---


# Question
Title: How can I make chess interesting and fun for beginners and doubters?
I love playing chess, but I find that it is difficult to find people who are willing to commit time to play games with me. I'm not a great player (I've never memorized moves or openings) but I have played enough to know my way around. I invite people over to my apartment every week or so, and I provide drinks and snacks, but it seems that there are some common reasons people don't want to play:

* They aren't good at chess, or think it's too complicated to learn.

Sometimes, this answer is just a defensive comment so that when they do play they don't feel humiliated. But sometimes it is just an excuse not to play, and it doesn't matter how good I or any other opponents are. How can I convince people that they don't need to be "good" to enjoy playing a game?

* "It's too big of a time commitment."

This is sort of the same reason that nobody will play Risk or Settlers of Catan with me. Especially since we've all heard of games that last whole weekends--and in chess games can last years! But the reality is that they aren't willing to dedicate just an hour or two to the game, while they are willing to sit in front of a TV for that same time period and don't see it as a problem. How can I convince people that it's worth their time?

* "I'm a girl."

I think women tend to think a group of people playing chess will be a bunch of nerdy guys talking about and doing stuff they're uninterested in. How can this perception be changed?

* "Chess is boring."

I get this, because it looks kind of boring when you're watching, but once you get into it and you have a basic grasp of tactics and strategy, it's not boring at all. How can I help people see how fun chess really can be?

* Other reasons?

What are some other reasons people avoid playing chess? What are some strategies to help get people in the door for the first time, and what are some strategies to help people have a fun time on their first visit so that they'll want to come back again?

# Answer
You need to show them *how to win*! Letting them win, or going easy on them, I don't think is the answer. Communicating a few simple chess concepts can go a long way.

Here's how I would approach it (once they understand the rules):

* **play** a few games (noting the moves)
* show them **a few simple concepts** such as the pin and the fork, the three opening principles, knights in pawn holes and good/bad bishops, the concept of the king net, and *some simple patterns* such as the back-rank mate, KRRvK mate and the rook-roll, or KRvK mate.
* go over the previously played games and **spot these concepts appearing**.
* go on and **play some more** games and *note their improvement*.

The problem is, *most people have the mistaken impression that chess skill is directly related to intelligence*. Because it's common for people to underestimate their intelligence, they don't believe they will be any good at the game and will most likely lose, while at the same time being perceived to be unintelligent because they failed at chess — no fun at all.

The key is to show them how to win via the communication of a few simple chess principles, which has the added benefits of improving their self-esteem, while at the same time giving them a glimpse into the underlying, invisible-to-the-non-chess-player beauty of chess.
> 18 votes

# Answer
I agree with what @xaisoft had to say, but I wanted to add a couple of points. In general though, someone who doesn't want to play won't enjoy the game.

For those who do want to try, but are hesitant, there are a few things you can do. Over the last 10 years I have kept a board in my office and encouraged software developers (as well as others) working with me to play the occasional game. It's a great mental exercise and fun way to break up the day.

First make sure that everyone has at least one individual who is a near match for them. If you are just playing bad to try and not be too competitive to a new player they won't appreciate their wins. Instead try and find two people interested in learning to play. They can then enjoy playing against each other and use games against you to improve their skills.

Second, when possible set your board up away from distractions. When I have been successful showing the game to children it has usually been away from technology. This might be in a library, or park, or a quiet room in the house without computer/TV.
> 12 votes

# Answer
One thing i would consider is starting with endgames. Give them a king and queen against your king and a few pawns for starters, and then move to other piece combinations. This will help ingrain the piece movements and they will always be starting with an advantage and will feel accomplished when they figure it out. Also, this will help in teaching openings and middlegames because they will have the end in sight...i.e. they will know what material they need and how to win. This is actually a very common teaching method in the Russian school of chess.
> 9 votes

# Answer
Honestly, if someone does not want to play, I would not force anyone to play (don't get the wrong idea, I don't think you are doing this), but you can always attempt to try much shorter games at first, like 10 minutes, so you can keep someone's attention span. You never know, in 10 minutes, they may become more interested. I would also recommend not getting too involved in the game, maybe letting the other person get ahead in development or winning some of your pieces so they gain some confidence and want or desire to play more. This is a mindset that people have to get into and it can't change instantly. It's like a sudden weather change; people have to become acclimated to it. If all else fails, try going to a club where you find other chess players who would be willing to stop by and play some games. Good luck!
> 4 votes

# Answer
I tried to expand on things in the accepted answer. Although I find opportunities for pins & forks hard to come by so far. It's definitely nice to have the queen around for checkmates so you only need 2 pieces (or two rooks). Getting your pieces into the 4x4 (2x2?) squares in the center is a good tip. Trade when cramped (or ahead). Look for attacks by you and them. Watch out for stalemates, yuck.

don't let other guy set up traps

variety

less pieces

take advantage of a crowded king, his own pieces and the borders

get rid of queens and their rooks?

net king and not chase him

look out for back rank mate

weak f7 pawn?

it's not fun to get far behind on the score, although sometimes it's good to sacrafice at a loss

control most of the squares?

```
3 classic opening principles
  Bring Your Pieces into Play (back row)
  Insure the King (castle)
  Control the Center 4x4 area

```

https://www.ichess.net/blog/opening-development/

knights in pawn holes \[outposts\] bishop too - blocks pieces in front. (or a hole is an outpost that a pawn can't attack?)

An outpost is a square on the fourth, fifth, sixth, or seventh rank which is protected by a pawn and which cannot be attacked by an opponent's pawn, knight (or bishop) can occupy, not worth a trade with a rook https://en.wikipedia.org/wiki/Outpost\_(chess) https://www.thechesswebsite.com/chess-outposts/ https://www.youtube.com/watch?v=o1T7TuP0Ad0

good/bad bishops - has targets and is not blocked, trade bad for good if your bishop can only attack your own pawns and none of your opponent’s, then it’s a bad bishop. https://www.thechesswebsite.com/good-bad-bishop/

king net or mating net - It's when you surround the king, cutting off all means of escape before moving in for the kill. A mating net is when your pieces work together to prevent the opposing king from escaping a mating attack. https://www.chess.com/lessons/attacking-the-king-1/mating-net

back rank mate - check mate on first row In chess, a back-rank (corridor) checkmate is a checkmate delivered by a rook or queen along a back rank in which the mated king is unable to move up the board because the king is blocked by friendly pieces https://en.wikipedia.org/wiki/Back-rank\_checkmate

KRRvK mate - two rooks, king at edge, "ladder mate" or lawnmower https://www.chesskid.com/article/view/checkmate-101

KRvK mate - mate with one rook and king, takes longer, same link

https://www.quora.com/Is-it-possible-to-checkmate-using-a-rook-and-a-bishop-without-any-aid-from-the-king The only two piece combination that can mate a king by themselves are queen and any other piece (rook, bishop, knight, or even another queen), a rook + rook combination, or a knight and a rook if the king can be cornered.

\[for trading\] A pawn is worth one point, a knight or bishop is worth three points, a rook is worth five points and a queen is worth nine points. Getting far behind is not fun.

pin (or backwards is skewer) - 2 pieces in line, back one more valuable https://www.chess.com/terms/pin-chess https://www.chess.com/lessons/capturing-pieces/pins

fork - 1 can capture 2 https://en.wikipedia.org/wiki/Fork\_(chess) forks pins & skewers https://www.youtube.com/watch?v=42ZDFP8\_ySI

how to get pin/fork opportunities https://www.chess.com/forum/view/general/forks-pins-and-skewers
> 1 votes

---
Tags: learning, clubs
---


title: What is this trap in QGD?

text:
# Question
Title: What is this trap in QGD?
I recently watched an Eric Rosen video where he showcased a trap in the QGD. I do not remember what the trap was called. Here are the moves.

```
[FEN ""]

1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. Bg5 Nbd7 {The trap is this move, because the d5 pawn is not actually free} 5. cxd5 exd5 6. Nxd5 Nxd5! {And White falls for it!} 7. Bxd8 Bb4+! 8. Qd2 {White is forced to give up their queen since that is his only move} Bxd2+ 9. Kxd2 Kxd8 {Black is up a knight, and has a safer king than White, and White’s only compensation is a pawn. Lichess’s Stockfish rates this to be ~-3.}

```

I don’t remember the name of the trap. If anyone could let me know that would be great. (Bonus points for anyone who can link me the Eric Rosen video!)

# Answer
This is known as the Elephant Trap.
> 12 votes

# Answer
This trap is the Elephant Trap.

The video is:

Crazy Queen's Gambit Declined and Secret Preparation Revealed
> 7 votes

---
Tags: queens-gambit, trap
---


# Question
Title: Can luck be used as a strategy in chess?
Consider below games where white looses a clean rook quite early in the opening but fights on hoping that they will be lucky and escape. Lucky enough, they escape and win the clearly lost game.

```
[Event "Rated Blitz game"]
[Result "1-0"]
[Variant "Standard"]
[TimeControl "300+0"]
[ECO "B21"]
[Opening "Sicilian Defense: McDonnell Attack"]
[Termination "Normal"]
[Annotator "lichess.org"]
[FEN ""]

1. e4 c5 2. f4 { B21 Sicilian Defense: McDonnell Attack } d5 3. e5 Bf5 4. d3 d4 5. g4 Bd7 6. f5 e6 7. Qf3 Bc6 8. Qf2 Bxh1 9. Bg2 Bxg2 10. Qxg2 Nc6 11. Nd2 Qh4+ 12. Kf1 exf5 13. gxf5 Nh6 14. Ngf3 Qg4 15. Qh1 Qxf5 16. b3 Be7 17. Bb2 Nxe5 18. Re1 Bd6 19. c3 O-O 20. cxd4 cxd4 21. Kg2 Qg4+ 22. Kf2 Qf4 23. Re4 Nxd3+ 24. Ke2 Nxb2 25. Rxf4 d3+ 26. Ke3 Rfe8+ 27. Ne4 f5 28. Rh4 fxe4 29. Ng5 Nf5+ 30. Kd2 e3+ 31. Kc3 Be5+ 32. Kb4 Nxh4 33. Qd5+ Kh8 34. Nf7+ Kg8 35. Nh6+ { Black resigns. } 1-0

```

I have heard in the past that '**It is noble to resign**' but if we fight on the stars may be aligned and luck come our way. Can we say that using luck may work as a strategy?

# Answer
> 23 votes
Whether or not to resign is a question of sportsmanship rather than strategy, I would argue. Just according to the rules, you are never forced to resign and can play on until you are checkmated (or someone is stalemated). However, it is expected (to a certain degree) that you resign in a position that is "clearly" lost.

There is no definite definition when a position is "clearly" lost though. If I am down a rook against Magnus Carlsen, I would definitely resign, because the chances of Carlsen blundering and giving me an opportunity to turn the game are infinitesimally small. Similarly, if Carlsen were able to gain a pawn without me gaining any compensation for it, I might resign as well (especially if it were the endgame). Again, Carlsen is expected to turn this advantage into a win eventually, and hoping that he will make an unrealistic mistake would be poor sportsmanship. On the other hand, if I was playing an opponent of my strength level, then a single pawn advantage might not be enough for him to find the win (even though the game might be already lost at perfect play). Instead, I would continue playing against my opponent until he demonstrated that he is aware of how to utilize the advantage to create a win (e.g., by creating a passed pawn that I can only stop by sacrificing another piece).

# Answer
> 15 votes
I believe there are quite a few distinct points to make to properly answer the question. @QueensKnight already adressed the "playing in a lost position" part of your question, so I'll focus on the "luck as a strategy" part.

## 1) Strategy hinges on reducing unknown or uncontrollable factors

When making a plan to achieve a certain goal (in chess or in life), it's important to make sure that it can be relied on at any point, otherwise there would be no point in following it. Often, it's impossible to guarantee the result because some factors escape our knowledge or our detection, but despite that minimizing such factors remains the best way to improve the strategy, by reducing odds of undesired outcome from unexpected events.

In stark contrast, relying on luck takes the exact opposite approach : decide nearly nothing to achieve the goal, hoping to reach it through favorable coincidences. Whether a good thing or not, it's clear that following this pattern is too different from a strategy to be called such.

## 2) Chess is a deterministic, perfect information game

When two persons play a game of chess, every move has always predictable impacts on the board. Pieces always move the same way, and capture the same way, pawns promotion condition and choices are the same, checkmate is always an inescapable check to the King, and so on. Furthermore, no information is hidden from either player : they see both their and their opponent's pieces at any time, see every move, and can contemplate their position as long as their clock time allows before the next move.

So under these conditions, there is simply no place for luck to occur inside the game, as there's neither random elements, nor unpredictability from lack of information. Hence, it makes little sense to play random moves when, at least in purely theoretical conditions, it's possible to analyze every variation down to their final result to give them as objective an evaluation as possible.

## 3) Playing the game or playing the player?

There is however one crucial factor that decides how a game of chess proceeds : both players. Chess is not an abstract thought experiment, but a concrete event shaped by the players. Of course, humans and machines alike have yet to solve chess, and even then it's not trivial to approximately evaluate a position at any level (depending on your error tolerance). This means that both players must carefully analyze the board to find which move they prefer, when they could play any move at all.

This gives room for outcomes that would defy the logic of "both sides play perfectly". Here are a few examples :

* Loss of focus : One player misses a possibility in a deep variation because they failed to consider it at all.
* Exhaustion : After playing for hours, a player cuts their evaluation short because they're too tired to think further (the risk of erroneous conclusions would be too high).
* Overconfidence : A player doesn't deem it necessary to analyze a position further, because it appears good enough at first glance, or because they believe their previous analysis, despite not being exhaustive until the final result, is still valid and isn't worth updating.
* Distraction : An event happens outside of the game that catches the player's attention (could be as simple as thinking about lunch), interrupting their thought process; when they resume their analysis, though it's not always the case, they might forget some important detail they had uncovered earlier.

And so on. Because the execution of each move in the game isn't guarantee, if only from the psychological side, and because it's not realistic to guess the opponent's mind (chess would be quite boring otherwise), there's room to believe the opponent could slip up for such reasons, which is what "being lucky" in chess really means.

## Conclusion

There's no luck in the game of chess itself, and even if there was, counting on it rather than doing everything possible to reduce losing odds can't be qualified as a strategy. From this, I'd say that **luck cannot work as a strategy**. However, it's not possible to tell either what's the opponent's state of mind (outside of very obvious clues), so there's always the possibility that they could make an uncharacteristic blunder for a variety of plausible, human reasons. Which means **luck plays a role at the human level**.

So it's true that that as long as you play, there's still at least a small possibility to win, while resigning will always be a loss. Still, no matter if there's the slimmest of chance for such a "lucky win", remember that it's not only out of your control, but there are the same chances that you could be affected by it in the opposite way get an "unlucky loss" (I know I've had my fair share of blunders that I'd readily qualify as such on the mental aspect). Is it worth spending time moving pieces hoping for the best then?

I'd suggest, when you're in a lost position and willing to play further, instead of just hoping for a blunder from the opponent, to try your best, keep a positive attitude, and hang on in the game. Sure, the opponent might still blunder, but they're far more likely to play well until the end (and the gap for this likelihood widens with the player's rating). But a very important thing in chess aside from winning is **learning**. Try to survive as long as possible after a big mistake. Try not to make another. Pay attention to the board and your mindset. If your opponent could mess up and lose the advantage if they don't find the one good move in a certain variation, try it out (forcing them to demonstrate their ability at converting an advantage, see @QueensKnight 's answer). Just do your best and learn from it. This will 100% be more valuable than simply hoping for a "lucky" outcome.

# Answer
> 6 votes
No, luck cannot be used as a strategy, as by definition luck is randomly distributed and *outside of your volition*; whereas conversely by definition a strategy is some method or plan designed and deployed *under your volition* to gain advantage.

# Answer
> 6 votes
Relying on luck as a strategy **may** work, but not as often as sound calculation and intuition. Therefore, **luck should not be your primary strategy**.

As another answer said, chess is a game of perfect information, so luck would arguably only exist in the inaccuracies committed by players who are making suboptimal moves. These could be called unlucky, or random.

However, the context of your question is about deciding whether to resign or play on when you have lost significant material or reached a clearly losing position. Asking yourself these questions can help you make that decision:

* **How much time remains in the game?** In shorter time controls where there is no increment, or if there remains, say, less than 5 minutes on their clock, even a strong opponent can blunder: *lucky* for you! So it may be worth playing on and trying to complicate and confuse the position to induce them to make a mistake.
* **How strong is your opponent compared to you?** If you are both amateur or untitled players, say, below 2000 rating, or if your opponent is much weaker than you, there is a higher chance of a blunder that could reverse the position.
* **Is this game part of a match?** If you have many more games to play, you may want to conserve your energy by resigning and focusing on the next game, where you'll have a fresh start.
* **Is this just a game for fun?** To some extent, *all* chess games should be for fun. But in a more serious game, you might want to press on, especially if there is a prize on the line.

# Answer
> 6 votes
**Clearly the situation you describe has nothing to do with luck.** Instead, it is simply bad play by black who cannot turn a decisive advantage into a victory.

The question in the text is actually:

**Are you allowed to make strategic use of your opponent's weaknesses?** The answer is of course "yes, absolutely!". But framed this way it becomes clear just why it is bad sportsmanship not to resign when one has clearly lost: *Because it betrays that you think your opponent is an idiot.* Consequently not resigning becomes worse sportsmanship with better opponents. (As an aside, in the game of Go an entirely decided game can be drawn out for a long time if the loser refuses to accept defeat which is therefore much more annoying than in chess.)

An interesting side question is: **Is there at all a luck component in chess?** It seems obvious that there isn't because chess is a complete information game with no random input. But I'd make the case that there is something *resembling* luck because while all information is available — after all, the board is right there! — the path of perfectly *utilizing* that information is *not.* **Chess is not solved.** That means that our assessment of positions is imperfect. The superiority of one move over another may only become apparent later. It was always superior, mind you; but we didn't know. This is where luck comes in: We may be lucky and choose a move that later turns out to be great. This kind of luck plays a greater role with weak players whose positional knowledge and analytic capacity is limited. Chances are that a strong player would have recognized the superior move — in fact, this ability is what defines a strong player.

Now to your title question: **Can this kind of luck be used as a strategy against a stronger player?** That is questionable. It won't work in simple positions with clear paths forward: Those will be understood well by the strong player, hence there will be no bad surprises for them later. This kind of luck therefore can only work in complex positions in which even the strong player's predictive depth is limited. But unfortunately even the limited prediction, the intuition and the experience favor the strong player in complex positions. A weak player with an inferior understanding of the complex position will have a hard time conjuring up a lucky turn that the strong player could not prevent in time.

# Answer
> 4 votes
Well, you can't plan on luck. Either it happens or it doesn't. It could also be bad luck for that matter, so I wouldn't rely on it to win any games. As far as resigning prematurely is concerned, that can be a mistake if you still have some fighting chances. It was Tartakower I believe who said you can't win by resigning. But they have to be legitimate chances based upon your situation in the game. If you're in a hopeless king and and pawn ending for example, that can be insulting to a decent opponent if you refuse to resign. But if you'e only down a minor piece early in the game and have no other weaknesses, I certainly wouldn't resign then but would keep making the best moves I could, which I have done in some games favorably. Then your opponent could potentially blunder. If that's what you refer to as luck, then I won't argue with you.

# Answer
> 4 votes
"Luck" is a bad wording. You can "push your luck", though.

* If you are a good tactician, and preferrable your opponent isn't, turn the board into chaos. I won games a rook down and no real swindling chances that way, and am reknowned as being lucky.
* Fight. GM Niclas Huschenbeth is a well known "lucky" fighter. I had him on the verge of loss about each time we played, and if I were a GM myself, probably I would have won each time. Most other GMs (even knowing my renommee as occasional GM killer) would have soiled their pants and offered me a draw. Not Niclas.
* Just by pure statistical variance, some people seem to be "lucky".
* A whole book "Luck in Chess" was written by Edward Winter, it might interested you (and I think it isn't the only one on that sujet.)

# Answer
> 3 votes
There are times when adding a random variable to a game of skill can actually help:

Let's take a simple example with the game even and odds. In this game you and your opponent hold up one or two fingers at the same time. If the total is even one person wins and odd the other. Let's say your opponent is really good at getting into your head and they are winning about 75 percent of the time. They decide to make a bet: if you win you get $1.10 and if they win they get $1.

Obviously if everything continues as before you will probably lose a lot of money but there's an easy trick you can use that guarantees your success in the long run: flip a coin. By doing so you've introduced a random variable ( that has variance, also known as luck) that completely eliminates their skill based advantage! You can also use this approach in poker when facing a far more skilled opponent. In fact, more experienced poker players often find it easier to play someone slightly worse than them compared to a complete beginner exactly because they are so unpredictable.

All that being said, these examples are of games where there is a large amount of randomness built in, you are given incomplete information, and you are given favorable odds. I think it would be very hard to work this approach into chess, which is a very different beast.

Note: the examples here are roughly paraphrased from a poker book by poker expert Sklansky.

# Answer
> 2 votes
Just a few examples of GMs talking about luck in chess.

Kasparov: in chess everything is visible but the result is random (as opposite of election in Russia, where everything is hidden but the result is certain).

Seirawan: it's very hard to win a winning game. If I can win all those winning positions, my rating points would be 200 higher.

Tal: Some sacrifices are sound, the rest are mine.

You would also remember women world champion Ushenina failed to deliver B+N checkmate.

I myself once lost a game like this

```
[fen "1r3k2/p4pp1/8/8/8/P7/KPQ3P1/6q1 w - - 0 1"]

1. Qc5+! Kg8?? 2. Qxg1

```

So randomness is actually part of the game and try your luck by all means.

# Answer
> 1 votes
## How does one actually *use* luck?

In game theory a lot of real world data is discarded in favor of simplifying the problem we are trying to model (and usually it is assumed both players play to the best of their abilities). A lot of things that affect both players are ignored, because they are not easy to model. Such things are: concentration, familiarity with positions, preferences, skill with each piece, memory, time, etc.

Another important point is that player skill is not something static, ratings should always be considered estimates of true skill, which is pretty difficult to measure since it can vary from game to game and even during a game. But it can be said that highly skilled players commit fewer mistakes than less skilled players.

In other words, it can be said that we are hoping our opponents commit mistakes we can identify and exploit in all games, so in this sense, **all players could be said to be always trying to or using their luck all the time** and the fact that a player committed one or more bad moves doesn't change that. To notice a mistake committed by an opponent is another one of those skills that are difficult to measure, so is the skill to punish a mistake.

## Luck as randomness

White could have lost the game, it also could have ended in a draw. There was no guarantee that 'luck' or randomness would be 'in favor' of any player. So just as white gambled and won, it could have been a loss instead.

In this sense, **no player can actually *use* luck**, because it is not a component a player has any control over as both players are subject to randomness.

## The place of sportsmanship

That being said, what role does sportsmanship play? *In my opinion* sportsmanship plays the role of respect/politeness. During a game, if **both** players agree the game is over and its result, wouldn't it be better to just start a new one? It's another thing entirely if there is no agreement. And the reason for both players not agreeing doesn't matter, though agreeing on the result is just usually faster.

---
Tags: analysis, strategy
---


title: Major Chess 960 tournaments?

text:
# Question
Title: Major Chess 960 tournaments?
Does anyone have any information about upcoming Chess 960 tournaments at the top level (i.e. GMs and IMs)? Even links to/information about past, major tournaments would be appreciated. I recently learned about Chess 960, and find it quite fascinating. I am also of the opinion that it would be more interesting to follow/study than regular chess early on in the game (since opening theory in regular chess goes as far as 25-30 moves in some openings), and beautiful novelties such as Aronian-Anand, 2013 can be prepared at home.

# Answer
> 8 votes
Present
2nd Chess 960 World cup to be played on Feb 15th,2013. The winner qualified as World Championship Candidates. This link shows the schedule for the 3rd and 4th Chess 960 World cup.

Chess960 news from the US CHess federation website. Talks of past and current events.

Past
Here is information about a past international FiNet Chess 960 open which was won by Alexander Grischuk of Russia.

Chess960 World Rapid Chess Championship
Nakamura simply won the first three games to become new World Champion – in a very convincing manner. Link also has games information and pictures as well. This is his website which has the blog and twitter account which can hopefully guide you to what events he participated in the past as well as plans to.

Chess960 World League 2012 by Chess.com
Team Armenia won this. Here is more information

Here is the Chess960 World League 2013 Information

Additionally searching on Chessbase.com would yield more news of past championships. chess960frc.blogspot.com is a specific blog on Chess960.

# Answer
> 0 votes
And now in 2021 obviously there's

FIDE World Fischer Random Chess Championship 2019

https://en.wikipedia.org/wiki/FIDE\_World\_Fischer\_Random\_Chess\_Championship\_2019

Chess 9LX

https://www.uschesschamps.com/2020-champions-showdown-chess-9lx/overview

---
Tags: tournament, chess-variants, chess960
---


# Question
Title: How is mate guaranteed - Bobby Fischer 134
I am working through *Bobby Fischer Teaches Chess* and #134 asks

> If White plays Rook-takes-Rook-check, can he mate?

The answer is Yes, the mate is delivered by the white Queen. However, can't it be prevented?

Here's the board:

```
[title "Bobby Fischer #134"]
[fen "1r1r2k1/6pp/2n4q/2p1p2Q/pp2N2P/5P2/PPPR2P1/1K1R4 w - - 0 1"]

```

I can see how to get mate, with the Queen: 1. Rxd8 Rxd8 2. Rxd8 Nxd8 3. Qe8 for mate.

However, if 1. Rxd8 Nxd8 2. Rxd8 Rxd8 . This *prevents* the Qe8 mate, doesn't it?

So when the question asks "can he mate", yes but it's not guaranteed. Do I understand the board correctly?

# Answer
> However, if black takes with Rook, then Knight takes' white's rook, white rook to take knight, then black rook to take white rook. This prevents the Qe8 mate, doesn't it?

No, it accelerates it. Let's look at what happens if black takes with the knight instead of the rook

```
[fen "1r1r2k1/6pp/2n4q/2p1p2Q/pp2N2P/5P2/PPPR2P1/1K1R4 w - - 0 1"]

1. Rxd8 Nxd8 2. Qe8# {oops!}

```

Black gets checkmated in 2 moves instead of 3
> 25 votes

# Answer
The objective is *not* to eliminate the rooks.

The objective is to **remove black's defense of the `e8` square** so that `Qe8#` can be played.

After `Nxd8`, does black still control `e8`?
> 17 votes

# Answer
White wants to play Qe8 for a back rank mate (since the Black king has no escape square). To do so, he must eliminate Black's protection of the e8 square. Capturing both rooks accomplishes that by 1. Rxd8+, Rxd8 2. Rxd8+ Rxd8 3. Qe8 mate. But if he plays 1..., Nxd8 instead of 1..., Rxd8, he interrupts the other Black rook's protection of the e8 square, and White is able to mate a move sooner by 2. Qe8 mate.
> 4 votes

---
Tags: checkmate, study
---


title: I need help understanding this puzzle

text:
# Question
Title: I need help understanding this puzzle
With White to play, I have trouble understanding what goes on in this puzzle. First of all, how exactly Kh1 is preferable to Kxh2? I know that Black can give checks after Kxh2, but there really is no mate threat anyway and White gets rid of a pawn that way. Also, why does Black follow up with Qe3, which leads to them losing a piece? Is there not a better move for them to play?

```
[fen "1r5k/1p5p/p5p1/2P1rRq1/P2Q4/8/1P5p/5RK1 w - - 0 2"]

1. Kh1 Qe3 2. Qxe5 Qxe5 3. Rxe5

```

# Answer
> 3 votes
**1. Kxh2** allows Black a forcing sequence exchanging off the pieces and White loses his big advantage: **1... Qh6+ 2. Kg2** now Black can capture the Rook on f5 and force a trade of queens: **2... gxf5 3. Qxe5+ Qg7+**.

---
Tags: tactics, beginner, puzzles
---


# Question
Title: CNN autoencoder for feature extraction for a chess position
I'm currently building a chess engine in my free time while entering my second year of my master's studies in computer science. For a class we need to perform a litterature survey of a topic and identify a research gap. I thought I'd kill two birds with one stone and research something relevant for the heuristic evaluation function of my chess engine.

What I want to do is to test the idea of using a convolutional neural network autoencoder to extract a feature vector (10-20 features maybe?) from chess boards. My idea is to encode positions in 8x8 arrays with each layer containing zeros or ones for each colour and piece, i.e. one layer for white pawns, one for black knights etc. Possibly it would also be good to have a layer indicating whose turn it is to move, and maybe 12 additional layers for possible squares of attack for the different pieces.

I can find tons of articles using convolutional neural networks for chess state evaluation (when searching scopus and google scholar), but nothing about using autoencoders. My idea is to append custom features (features that might be difficult for a CNN to find) in addition to the autoencoded features, and then feed all features to a new model. Has this been done before? If so, can someone point me in the direction of some attempts at this?

People who are versed in chess and in CNNs, what features for a chess board are difficult for CNNs to automatically detect, that would benefit from some custom feature engineering alongside an autoencoder?

Also, can someone see some obvious weakness with this approach, or does it seem like a sound idea?

# Answer
> 2 votes
I'm very late but I am working on something similar. Here are are a couple of resources that involve using autoencoders.
https://chessvschessproject.wordpress.com/
https://arxiv.org/abs/1711.09667
https://github.com/oripress/DeepChess

Hope they help! Let me know how it goes.

---
Tags: engines, analysis, programming, evaluation, mathematics
---


# Question
Title: What is the correct hand movement to capture a piece?
I see players in international tournaments taking pieces in the following fashion: first they take off the board the piece they intend to take, and only then, with the same hand, they move their taking piece in the square occupied by the removed piece (except in en passant, of course).

I was taught to take pieces using a single hand movement instead: I move my taking piece to the square of the piece to be taken and remove that in the same time putting it off the board.

Since I think that the first method is more time consuming, I am assuming that it is the only legal method to take pieces, while mine must be illegal. Am I wrong? Or does it depend on the particular policy of each tournament?

# Answer
Short answer: Their movement is cleaner than yours, but not more legal.

Longer: When you shove aside a piece with your capturing piece, it risks affecting the placement of the pieces around it. It also risks accidentally causing you to touch other pieces, bringing some other conflict into the game. So, all things considered, your way risks causing more issues than their way, but neither way is more legal than the other.
> 9 votes

# Answer
According to the FIDE Laws of Chess:

> 4.1 Each move must be played with one hand only.

In other words, the "correct" hand movement is one which uses only one hand. The order in which the opponent's piece is removed and the player's own piece moved to the capturing square is irrelevant.

Note that once the captured piece has left the board it doesn't matter which hand is used to place it on the side. It is perfectly legal, for instance, to lift the piece from the board with the right hand, immediately transfer it to the left hand and carry it to the side of the board with the left hand whilst simultaneously moving the capturing piece to the capture square with the right hand.

Something similar applies with promotion. The promoted piece must be placed on the board with the same hand that removes the pawn from the board but it is perfectly legal to pick up a queen, say, with one hand whilst removing the pawn with the other and to transfer the queen from one hand to the other before placing it on the promotion square.
> 13 votes

# Answer
I believe either way is fine. I have seen both, but not in blitz.

FIDE

> 4.6 When, as a legal move or part of a legal move, a piece has been released on a square, it cannot be moved to another square on this move. The move is then considered to have been made:
>
> a. in the case of a capture, when the captured piece has been removed from the chessboard and the player, having placed his own piece on its new square, has released this capturing piece from his hand
> 5 votes

# Answer
Either method is completely fine, do whichever you're more comfortable with. There are a few "pros" and "cons" of each, but they're more or less non-factors:

Taking the piece you intend to capture off first may look more "precise", since the other way involves scraping the pieces together. There's also the small issue of touch move. What if at the very last minute you change your mind? If you've touched your piece first, you'll have to move that piece somewhere. Meanwhile, if you've touched your opponent's piece first, you'll have to capture it (with either the piece you intended or another piece, if one's available). In such a scenario, the method you use will probably give you a higher degree of freedom on average.
> 4 votes

# Answer
The first method that you describe is cleaner, but only after a bit of practice. Therefore, many players use it to convey an intimidating air of experience.
> 2 votes

# Answer
It seems obvious to me: if it is your move then you MUST touch your own piece first; pick it up with one hand and then pick up the target piece with the same hand and place your capturing piece on the vacated square - although this may require a tiny bit of finger control so be it. The comcept that if you pick up the target piece first, providing options for the piece to capture, is erroneous - nowhere in the rules are you entitled to this afterthougt privilege, you can't go willy nilly touching opponents pieces out of order, that is an unforgivable misbehavior worthy of disqualification. Can you imagine a scenario where a player simply keeps picking up the opponents pieces and then sits there for minutes on end, contemplating what to capture with? That dog don't hunt.

After a capture it is often seen that a player uses the captured piece to hit the clock - this is a legal and harmless expression of intimidation, as well as it saves time (especially in blitz) insofar as it is not legally neccesary to put the captured piece down on the table immediately after capture.
> 0 votes

---
Tags: rules, captures
---


title: Analysis of ng4 vs f4

text:
# Question
Title: Analysis of ng4 vs f4
Why is it that ng4 is the best move here? I played f4

# Answer
> 3 votes
It is a pretty forcing move, White does not have many options to react to it and all are painful.

The most obvious question, why cannot White take?

Because hxg4 Rh8+ is forced mate.

If Rook takes we just take Back, White has no meaningful checks and we are just up a rook.

Finally, if White dodges with Kh1 we take the knight, and White still cannot take ours due to Rh8+ being devastating.

```
[Variant "From Position"]
[FEN "r3r3/p1p3k1/1b6/5pN1/Q1Pp2n1/P2Pq2P/1P2P1RK/R7 w - - 0 1"]

1. Kh1 (1. hxg4 Rh8+ 2. Nh3 Rxh3#) (1. Rxg4 fxg4 2. Qd7+ Re7 3. Qxg4 Qxe2+ 4. Kg1 Qxg4+
5. hxg4)Qxg5 2. hxg4 Rh8+ 3. Kg1 Qe3+ 4. Rf2 Rh2

```

---
Tags: online-chess
---


title: Harry Potter Chess Analysis

text:
# Question
Title: Harry Potter Chess Analysis
So, I've been reading Harry Potter and The Philosopher's Stone. If you haven't read the book yet, or watched the movie, and you don't want any spoilers, stop reading this question. Continuing, there is this chess scene, where Harry, Ron, and Hermione had to play their way through a giant board. They were black. Harry became a bishop, Ron a knight, and Hermione a "castle" which I guess refers to the rook. Is there such game where it followed the conditions that the book said?

These conditions are:

* White starts with 1. e4
* The white queen takes both black knights
* The second black knight (Ron) sacrificed himself to the white queen in order for a bishop (Harry) to travel 3 spaces to the left for mate
* The first black knight was taken for a trade for a black rook (Hermione) to take a white bishop
* Both the bishop and rook (Harry and Hermione) were in danger twice
* The second black knight (Ron) took the most white pieces
* The same black bishop (Harry) went 4 spaces to the right in the opening

# Answer
> 7 votes
Jeremy Silman talked about the position in these 2 links in the description here.

https://www.jeremysilman.com/book-review/creating-the-harry-pottter-chess-position/

(also http://web.archive.org/web/20170801000000\*/jeremysilman.com/shop/pc/Creating-the-Harry-Potter-Chess-Position-87p3692.htm and http://web.archive.org/web/20111201000000\*/jeremysilman.com/movies\_tv\_js/harry\_potter.html)

Also for reference here's the position: 5r1k/1pN1R1pp/1Pb5/n1r1P1n1/7N/b2p4/7P/1R1Q2K1 w - - 0 1

---

And of course there's agadmator: Ron Weasley Sacrifices Himself for the Team

---

anyway, let's see if the game in the movie satisfies the conditions

1. White starts with 1. e4

* 1.1. Yes. Ron does Scandinavian defense.
2. The white queen takes both black knights

* 1.2. No, just Ron. But the other knight doesn't really do anything, so I don't see why there couldn't have been a position where Harry, Ron and Hermione have lost their other knight. An unlikely thing is that there was an early underpromotion.
3. The second black knight (Ron) sacrificed himself to the white queen in order for a bishop (Harry) to travel 3 spaces to the left for mate

* 3.1. Sort of. Yes, assuming (A) you don't count the intermediate move of capturing the queen (the movie didn't seem to count this!) and (B) if you count moving 2 squares diagonally as 3 total, like there are 3 numbers between 1 and 3 inclusive but it takes only 2 (+1)'s to go from 1 to 3. (referred in (7.2))
4. The first black knight was taken for a trade for a black rook (Hermione) to take a white bishop

* 4.1. see (2). Well, white doesn't have any bishops left, and Hermione maybe only moved a little after they presumably castled. Maybe there was a Bxf1 and then Hermione recaptured. However, Hermione has control of this really critical f-f-file to the point of blocking (I guess I don't mean 'blocking' in the chesstempo sense) the exposed white king's escape s.t. Hermione, Harry and the other bishop ultimately checkmate the king together. In fact, it's because of Hermione's control that at the start they already have this mate threat with a combination of Ron, Hermione and the other bishop.
    * 4.2. Btw in the movie, Ron says Hermione is the queenside rook ('queenside castle'), but it seems here Hermione is the kingside rook (unless maybe Ron did some kind of rook lift)
    * 4.3. Hey funny thing I noticed re Hermione and Ron:

    + 4.3.1. After Ron's offered rook (the non-Hermione rook) sac Rc3, the engine says the best continuation: is Qf5 (declining the sac but standing right beside Ron), Rxf5 (Hermione takes f5), and then Nxf5 (white knight takes Hermione) ! (referred in (5.2))
        + 4.3.2. An alternative to Hermione takes f5 is: Bc5+ (Harry c5+). The 2 best moves here are Rxf5+ (Hermione takes f5+), and Bxe7 (Harry takes e7), but Hermione seems to die in both of them. The 3rd best move Rf3+ (again, the non-Hermione rook) I think saves Hermione...or maybe not.
        + 4.3.3. Analysing the Qf5 line further makes me think white isn't necessarily playing to win (I mean the original Qxc3 is suboptimal) but more playing to get one of the intruders to be sacrificed or something.
5. Both the bishop and rook (Harry and Hermione) were in danger twice

* 5.1. Harry: Yes. Immediately before Ron checks king at end, Harry, as the dark square black bishop, is in line of sight of white queen.
    * 5.2. Hermione: Seems possible. There's no indication for Hermione in danger, but I don't see why there can't be a game like this. Hermione is of course in implicit danger (see (4.3.1)).
6. The second black knight (Ron) took the most white pieces

* 6.1. When playing a game, I don't know of anything where people keep track of which piece captured the most pieces. This sounds something like determining which piece is like the 'MVP', like the online pokemon TCG or csgo. I don't think this is a chess thing. But I guess it seems plausible.
7. The same black bishop (Harry) went 4 spaces to the right in the opening

* 7.1. Harry as the dark square black bishop could've done Bb4, like in Nimzo-Indian Defence, but Nimzo-Indian Defence is a response to 1.d4 and not 1.e4. Perhaps there's some variation of Scandinavian that involves Bb4. (Now looking it up...) Ah, found something. According to this, there's something called 'Scandinavian, Anderssen counter-attack orthodox attack' that goes

> 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 e5 5. dxe5 Bb4 6. Bd2 Nc6 7. Nf3

```
[White "Some 1.e4 player"]
[Black "Some Scandinavian player"]
[Result ""]
[FEN ""]

1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 e5 5. dxe5 Bb4 6. Bd2 Nc6 7. Nf3

```

Also, notice that before capturing the queen, Harry is along the same diagonal of b4 and Harry's starting square (f8). But actually 4 spaces to the right is a pretty common thing I think like Ruy Lopez. (I quit chess for chess960 a long time ago, so ask someone else.)

* 7.2. I think this is a lot easier if this means Bc5 instead of Bb4 (w/c might be what is meant based on (3), but I guess I'm wrong because there's no move Bc5 in the same link above or in wiki.

---

**Update**: Does Magnus Carlsen Remember the Position in Harry Potter Movie?

Here, Carlsen claims that the moves Qc3 and Nc6 were played. Not sure either of those moves were played, but in the Silman position Qxd3 (not Qd3 and not Qc3) and Nh3 (not Nh6) were played.

---
Tags: books, famous-games, 1.e4, retrograde-analysis, fiction
---


# Question
Title: Guide to understanding engine analysis output
Not having played for decades, I am getting back into chess, with all the great programs. I have Shredder 13 and Fritz 17. Both can output very impressive analysis. But for an effective newbie, where can one find out how to understand and interpret this detailed information? The manuals are totally missing any useful help. Apologies for such a newbie question, but the point is I would like to understand how I can improve my game by through the engine generated analyses. All I understand presently is the figure that represents the advantage estimate. There are tens of thousands of videos on chess. So far I have not found one dedicated to this topic.

# Answer
> 3 votes
I'm not sure what you're asking.

Chess analysis programs go through all possible moves for some number of (half-)moves starting from a given board position. They evaluate the static board position at the 'depth' to which they're set to analyze, and return a score for the position. This is not how any human plays the game, of course.

When the engine recommends a move, it is indicating that that move got the highest score among other moves possible from that position. Its static board evaluator might know about control of the center, or control of more space, or having two bishops, but it knows about them in terms of evaluating a single board position and scoring it, not in terms of deciding that that principle applies in a given situation and making moves on that basis. It's a subtle difference, I guess, but very real to the programmers.

Other than that, you get negative scores for Black advantage, positive for White, the numbers increase for more advantage.

In the end, about all you can do with the output of chess analysis is see the moves they regard as 'best' (and maybe 2nd and 3rd best) from any position and try to figure out how you would have known to make those moves and not some other moves. You can try other moves and figure out what would have happened, why they are worse.

If you have another question, can you make it more specific?

---
Tags: analysis
---


title: Series of illegal moves in check

text:
# Question
Title: Series of illegal moves in check
This question falls under FIDE rules (USCF answers/comments welcome).

If I make an illegal move leaving myself and my opponent in check, hit the clock and my opponent misses it and then continues play and hits their clock what happens?

So for example let's say I put my king on an adjacent square to my opponent's king and hit the clock, then my opponent moves a piece on the other side of the board leaving the kings checking each other and hits the clock, what happens here?

# Answer
The answer depends on whether or not the games are being recorded. The way this is elliptically referenced in the FIDE Laws of Chess is that a distinction is made between, on the one hand, standard time controls (where moves must be recorded by the players), rapid and blitz games played at a sufficiently high level that there are enough arbiters to record the games and on the other hand regular rapid and blitz where nobody is recording the rules.

In the first case article 7.5.1 applies and the games is restarted from the last known legal position and various penalties can apply.

> 7.5.1 An illegal move is completed once the player has pressed his clock. If during a game it is found that an illegal move has been completed, the position immediately before the irregularity shall be reinstated. If the position immediately before the irregularity cannot be determined, the game shall continue from the last identifiable position prior to the irregularity. Articles 4.3 and 4.7 apply to the move replacing the illegal move. The game shall then continue from this reinstated position.

According to Appendix A 7.5.1 also applies for rapid where:

> A.3.1.1 one arbiter supervises at most three games and
>
> A.3.1.2 each game is recorded by the arbiter or his assistant and, if possible, by electronic means.

And for blitz according to Appendix B where

> B.3.1.1 one arbiter supervises one game and
>
> B.3.1.2 each game is recorded by the arbiter or his assistant and, if possible, by electronic means

Otherwise for rapid and blitz (recording not done / not possible) illegal moves are not punished and not corrected unless either the arbiter or one of the players spots what has happened before another move has been made:

> A.4.2 If the arbiter observes an action taken under Article 7.5.1, 7.5.2, 7.5.3 or 7.5.4, he shall act according to Article 7.5.5, provided the opponent has not made his next move. If the arbiter does not intervene, the opponent is entitled to claim, provided the opponent has not made his next move. If the opponent does not claim and the arbiter does not intervene, the illegal move shall stand and the game shall continue. Once the opponent has made his next move, an illegal move cannot be corrected unless this is agreed by the players without intervention of the arbiter.

There is an additional twist for rapid and blitz to handle the position where the arbiter comes late to the scene and spots your last scenario:

> my opponent moves a piece on the other side of the board leaving the kings checking each other and hits the clock, what happens here?

The arbiter waits one move to see if the illegal position is corrected and if not declares a draw.

> A.4.4 If the arbiter observes both kings are in check, or a pawn on the rank furthest from its starting position, he shall wait until the next move is completed. Then, if an illegal position is still on the board, he shall declare the game drawn

If the arbiter doesn't see it then the game between Larry and Mo continues.
> 12 votes

---
Tags: rules, fide, check, kings, illegal-move
---


# Question
Title: Is there an engine that finds the best "practical" move?
A standard chess engine will find the move it considers best assuming best play from both sides. But this move might lead to an insignificant advantage or a tricky line that can easily result in mistakes for a human player of a specific ability. Is there a program that finds the best "practical" move for e.g. intermediate players? For example, it might pick a move that leads to a very strong attacking position where the opponent will most likely make a mistake, even though it could be defended against with perfect play.

# Answer
Update: Maia chess came out recently and it does something very similar to what I ask above. It tries to predict the most likely human move and at a given level. It seems Maia could be extended to create a program that finds the best practical move - given likely future human moves, it could figure out which move has the best "expected value".

Their paper: https://arxiv.org/abs/2006.01855

Play it: https://lichess.org/@/maia1
> 2 votes

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

The danger of contempt is, against a strong opponent, high contempt can get you killed - you are after all forcing the engine to play a weaker move just to keep the game alive.
> 26 votes

# Answer
I realized this question applies mainly to standard chess engines that use minimax functions to evaluate moves. However chess engines like alphazero use monte carlo tree search to simulate many different games so they're not only looking at the best possible moves. It's possible that they already could be used to find the best "practical" move, or that they could be adapted for that purpose. For example the monte carlo search algorithm could be updated to look at "reasonable" moves and simulate what happens.
> 6 votes

# Answer
Not really.

Databases are useful because they can tell you often a move is played and what the result is however they are not perfect for a variety of reasons.

Fritz 12 (not sure about later versions) has a "hotness" meter which tells you how complex a variation is.

Bottom line. it's a combination of things. You're looking for moves where the most principled moves turn out to be bad. No engine can tell you that.
> 1 votes

---
Tags: engines
---


# Question
Title: How is this not checkmate? I had loads of time to spare
See below my game last night, I am white and I got 3 queens. He only has the king left. We have loads of time left. It was a 30min game.

As soon as I moved my original queen up one space and got him into check mate, the game ended as a draw!

How is this a draw?

# Answer
A necessary condition for checkmate is that the king is in check, which is not the case here.

The position in question is called stalemate: black does not have any legal moves, but is not in check. The game ends at this point, and is evaluated as a draw.
> 8 votes

# Answer
It is stalemate (opponent's king can't move anywhere and not in check). Your queen move last move doesn't check his king.
> 2 votes

# Answer
You have to understand what a stalemate is. It is one of the ways a game is drawn. A stalemate occurs when it is your turn to move but you have no legal move. So if your king is not in check, but any move you make with it would put it in check, which is illegal, that is a stalemate, which is a draw. In the diagram showing your queen move from f4 to f5, you have not put the Black king in check. And you left him with no legal move on his turn, so it was a draw by stalemate.
> 0 votes

---
Tags: checkmate
---


# Question
Title: Two questions about Wesley So vs Varuzhan Akobian (2016)
Here is a link to the game itself.

```
[FEN ""]
[White "Wesley So"]
[Black "Varuzhan Akobian"]

1. e4 e6 2. d4 d5 3. Nc3 dxe4 4. Nxe4 Nd7 5. Nf3 Ngf6 6. Nxf6+ Nxf6 7. c3 c5 8. Be3 cxd4 9. Bxd4 Be7 10. Bd3 O-O 11. Qc2 h6 12. O-O-O Qa5 13. Kb1 Rd8 14. Ne5 Bd7 15. Qe2 Bc6 16. Rhe1 Bd5 17. c4 Bxg2 18. Bc3 Qb6 19. Rg1 Bc6 20. Nxf7 Kxf7 21. Rxg7+ Kxg7 22. Qxe6 Qxf2 23. Qxe7+ Kg8 24. Bh7+

```

I'm a chess newbie and was looking at this game and quite amazed by the White knight's attack. I have two questions.

First what point did Akobian go wrong? I really didn't see the attack coming. Only at 20. Nxf7 did I realize that the White knight must have some sort of plan and it was probably calculated way ahead. I assumed it was only on the next move that Akobian was also able to calculate ahead and see no chance of winning. But at what point was the game not saveable, at what point did Akobian make a big mistake? I have a very limited chess program, but it never gives the White knight a big advantage for any of the moves until then so I can't figure it out.

Secondly, did the White knight make a mistake at the end? My computer gives 24. Bxf6 as the better move, forcing a checkmate in just a few moves. Meanwhile, the line played by the White knight is not forcing, at least not immediately.

# Answer
> But at what point was game not saveable, at what point did Akobian make a (big) mistake?

Qxf2 is a big mistake as after that it is forced mate in 7 moves. If So had played 24. Bxf6 there is no defense against all the mate threads and all black can do is prolong his suffering by throwing in some pieces.

```
[FEN ""]
[Event "US Chess Championships"]
[White "Wesley So (2773)"]
[Black "Varuzhan Akobian (2615)"]
[StartPly "46"]
[Result "1-0"]
[PlyCount "47"]
[ECO "C10"]
[Opening "French Defense: Rubinstein Variation, Kasparov Attack"]

1. e4 e6 2. d4 d5 3. Nc3 dxe4 4. Nxe4 Nd7 5. Nf3 Ngf6 6. Nxf6+ Nxf6 7. c3      c5 8. Be3 cxd4 9. Bxd4 Be7 10. Bd3 O-O 11. Qc2 h6 12. O-O-O Qa5 13. Kb1 Rd8 14. Ne5 Bd7 15. Qe2 Bc6 16. Rhe1 Bd5 17. c4 Bxg2 18. Bc3 Qb6 19. Rg1 Bc6 20. Nxf7 Kxf7 21. Rxg7+ Kxg7 22. Qxe6 Qxf2?? 23. Qxe7+ Kg8 24. Bh7+!? (24. Bxf6 Qxf6 25. Qxf6 Bg2 26. Rg1 Rxd3 27. Rxg2+ Rg3 28. Rxg3+ Kh7 29. Qg7#)

```

However So did not play 24. Bxf6 but went for Bh7+ instead which is of course also winning. Most likely he saw that after Bh7+ lots of material would **come off the board** in a **forced line** and he would end up in an easily won endgame with queen plus 4 pawns vs. bishop plus 3 pawns (no counterplay for black and no fortress either).

While mating quickly is more desirable for the beauty of chess, from a practical standpoint, going for a forced line which is easy to calculate and obviously won makes a lot of sense. 24. Bxf6 of course looks very good even without calculating concrete lines, but has more potential for error. Furthermore if So had played 24. Bxf6, he would have needed a bit more time for calculating consequences of that move and also Akobian might have fought on for a move or two. So in the end the second best move (Bh7+) might even have ended the game quicker, because it was obvious that white will win.

## Back to Qxf2...

That's a curious choice as it leaves the bishop on e7 hanging and after that also the knight on f6 is hanging. I have no idea what Akobian was thinking here (probably desperation or time trouble?). He must (or should) have checked at least all the options of protecting the bishop on e7, like Qc5, Qc7, Re8 and Rd7. Both, Qc5 and Qc7 lose and it is easy to calculate this on the board. 22 .. Re8 seems to hold according to the computer. Black is still under a very dangerous looking attack and will have to find the correct moves to secure equality in the moves to come. 22 .. Rd7 will lose, but not as fast as 22 .. Qc5/c7. From a GM I would have expected to play one of Re8 or Rd7 at least.

## Did Akobian go wrong before Qxf2?

Computers give more or less equality (small advantage for white) before that move, but from a human perspective I find 17 .. Bxg2 a strange choice as it opens the g file for white's rook. This will always be dangerous even if there is no immediate tactics.

Also I am not sure whether transferring the bishop from c8 to d5 via d7 and c6 was such a good idea. Wasted lots of tempi just to force white to play c4. Probably a better plan for black here was to go for a minority attack on the queen side with b5, b4...
> 9 votes

# Answer
> the line WS played is not forcing, at least not immediately.

You have a funny definition of not forcing. The lines look pretty forcing to me.

First possibility:

24 ... NxB 25. Qg7#

Second possibility:

24 ... Kh8 25. BxN+ QxB 26. QxQ+ KxB 27. RxR RxR 28. QxR

leaving white with Q+4P v B+3P.

The aim of the game is to win not to copy the computer's best line. So won the game so by definition did not make a mistake.
> 3 votes

# Answer
Great answer by user1583209.

But my view is that the error was perhaps a series of small errors, so I don't put as much emphasis on Qxf2 as THE error though it was a big error still. In fact, if you use a chess engine, even if black plays Re8, it's still a losing game and the queen can continue to check the king as it regains its material advantage. Perhaps that's what Wesley So had in mind because otherwise why did he make those sacrifices (move 20 and 21)? He surely did not know that Akobian would play 22...Qxf2.
> 1 votes

# Answer
Moving the white-squared bishop around only to have it chased away again with c4 was already a dubious plan by Black, but 17. ... Bxg2 almost looks like a beginner move. Opening the g-file straight to the Black king like that is more or less a gift to White. 15. ... Rac8 looks more active, or maybe even 15. ... Be8 defending the weak f7 pawn and at the same time improving the position of the d8 rook.
> 0 votes

---
Tags: analysis, knights, master-games, wesley-so
---


title: Chess960 or Chess959?

text:
# Question
Title: Chess960 or Chess959?
Once in 960 times, Chess960 should just be the same as regular chess. Are there any known instances of this? Or is this selection automatically excluded, after which they just roll the dice again? So is it really "Chess959"?

EDIT: Found this: https://lichess.org/forum/lichess-feedback/chess960-starting-position-518-is-like-regular-chess. An online player complains that he has faced the dreaded 518 two times. And why not? My golfing uncle hit two holes-in-1 during his career, and that’s got to be a lot less likely than 1 in a thousand!

But I think that Chess960 can’t be that popular at top levels or there would be a celebrated example where GM X faced GM Y over a 518 Game Array.

# Answer
> 25 votes
There is no mention of excluding the regular starting position in Appendix F. of the FIDE Laws of Chess, so it's really Chess960 and not Chess959. I can imagine that there are chess programs or websites which do exclude the regular starting position, but this is against the official rules.

# Answer
> 9 votes
There is a "Chess959" which advocates the removal of SP 518 (which is when the factors that lead to "randomizing" the chess pieces happen to have the same arrangement as the traditional layout.) The rationale for removal is that players have so much training in that one starting position that the game becomes less about who is the better, more reactive OTB chess player and more about who has prepared their opening lines.

Assuming both players are actively participating in Chess959 as opposed to 960, in the event of rolling SP 518, simply re-roll.

# Answer
> 6 votes
**2019 Update**:

From 'Regulations for the 2019 FIDE World Fischer Random Chess Championship', it's excluded:

> If during the event the start position of classical chess is selected, the draw for the initial setup of the pieces will be done again.

**Even 2022**:

Also Regulations for the 2022 FIDE World Fischer Random Chess Championship

> If the start position of classical chess is randomly selected, the draw for the initial position of the pieces will be repeated.

---

Check out:

Chess959 not Chess960 ! See in 2019 and 2022 regulations that FIDE's World Fischer Random Chess is actually Chess959. Now can lichess please do the same?

>

---

2024 Update:

In 2024Feb Freestyle Chess (GOAT not MTOAT I guess):

https://www.chess.com/news/view/2024-freestyle-chess-goat-challenge-day-1

> the way the position is drawn using 958 balls (the normal chess position, and the same position with queens and kings swapped, are excluded)

So SP518 and gender-swapped SP518 (SP534) are out.

---
Tags: chess-variants, chess960
---


# Question
Title: Why is bishop to h8 the best move in this position?
I don't understand how that move is a good move, much less the best move according to this chess.com analysis.

# Answer
> 1 votes
The picture already answers the question:

If you play any other move but **...Bh8**, for example **...d6**, White will answer **g4** and trap your knight. Some exchanges can be thrown in before he can capture (**dxe5**, **Qxd1** etc.), but ultimately, there's no escape.

**...Bh8** by itself is indeed not a desirable move (moves a developed piece again, to a square with less influence), but here it's a tactical necessity to save that knight (which is more valuable than losing a move or two) by vacating an escape square.

Since White is behind in development, Black can actually afford to give that tempo without major damage (+0.31, says the computer).

# Answer
> 6 votes
The knight on h5 has no retreat squares, which means the threat of White playing g2-g4 is on the cards. The move **... Bh8** then frees up the g7 square so the knight has a retreat square should it be attacked.

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Tags: opening, analysis, beginner, kings-indian
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title: Why does Stockfish recommend Kg2 here?

text:
# Question
Title: Why does Stockfish recommend Kg2 here?
When I turn on threat analysis and it gets to a depth of 24, it says Black wants to play Qe7 or Nh7 (after the latter, White's recommended move is again Kg2). I imagine the point of White's move is to prevent something from happening, maybe some attack along the semi-open f-file, but I don't really see any concrete moves for Black that would require White to play Kg2 with such urgency.

# Answer
I realised as I finished typing up my question that if White wants to trade off the knight for a Bishop (thus retaining the bishop pair, which is good for reasons, probably) White can't just play 3.Ne5 immediately, because after 3...Bxe5 4. Bxe5 Black can play 4...c4!, and now threatens to fork the king and the bishop. For example, you could continue 5. Qxc4 Rc8 6.Qa6 Qc5+, after which White is still better, but then Black has counterplay and active pieces (e.g. Black can play ...R8d8 and have pressure along the d-file, and apparently ...Ng4 is playable as well, but I don't understand that line).
> 3 votes

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Tags: analysis, prophylaxis
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title: Which collections of pieces are legal?

text:
# Question
Title: Which collections of pieces are legal?
Call a collection of (white *and* black) chess pieces *legal* if it occurs in the position of a legal chess game. For example, `KQRRBBNNPPPPPPPPkqrrbbnnpppppppp` is the collection at the beginning of the game. It seems any subset of this (still containing the two kings) is possible as well. But sometimes you can have lots of promotions, so for example `Kkqqqqqqqq` is possible if black promotes all eight pawns to queens while all other pieces are captured.

**Which collections of pieces are legal?**

This answer on MathOverflow conjectures/states without proof that the legal collections are those that can be obtained from the starting collection using the following two operations:

1. Delete any (non-king) piece and promote at most one white and at most one black pawn.
2. Delete a pawn and promote at most one pawn of the same color and at most two pawns of the opposite color.

Is this characterization correct?

# Answer
Yes the characterization is correct, and there are 58,084,310 legal collections in total.

To make headway, we need the right level of discourse, avoiding loss of accuracy while avoiding diving into trivialities.

**Necessity & sufficiency of the deletion moves**

Two kinds of operation were suggested to be necessary & sufficient to reach all legal collections:

```
(1) Delete a (non-K) officer & promote at most 1 wP and 1bP
(2) Delete a P & promote at most 1P of that color and at most 2Ps of the other color.

```

Firstly, the two criteria are necessary. To unblock a file a capture must take place. Capturing an officer will allow both pawns from a file to promote. A pawn capturing a pawn from a neighbouring file is more efficient, as it allows three pawns to promote.

The condition is also sufficient, as can be seen by dividing up the board into 4 pairs of files. We have to make assumptions that the kings can keep out of the way of the action. See later for an example which explores the validity of this assumption.

**"Supply & demand"**

Maybe worth moving on to the question of which collections are achievable in this way:

1. Count the number of visible "non-starting officers" for each side (queens beyond the first; other officers beyond the second of that type): N\_w & N\_b
2. Count the number of "awol pawns" on each side: (pawns morphed into NSOs aren't counted): A\_w & A\_b
3. Count the number of "missing officers" for each sides (missing queen, or other officers less than the second of that type): M\_w & M\_b

Then the following elegant "supply & demand" inequalities are necessary and sufficient criteria for a legal collection:

```
M_b + 2*A_b >= N_w - M_w - A_w
M_w + 2*A_w >= N_b - M_b - A_b

```

Grouping the terms by White & Black, the left hand side is the "supply", the right hand side is the "demand". The supply is always non-negative, so if the demand is zero or less, it's always satisfied. Similarly, a supply of 8+ will meet any demand that can occur.

Here's an example. Can we have 18 queens on the board? Yes!

```
N_w = N_b = 8
(because 8 promoted pawns on each side)

A_w = A_b = 0
(every missing pawn was promoted)

M_w = M_b = 6
(all Rs, Bs & Ns were captured)

M_b + 2*A_b >= N_w - M_w - A_w
translates to:
6 + 2*0 >= 8 - 6 - 0
6 >= 2

```

So this is legal. Similarly for White supply for Black demand. Even if we had the knights still on the board, so M\_b = M\_w = 4, the inequality would be 4 \>= 4, so still legal.

**Aside on mate/stalemate**

Some wonder if such a position can be achieved without mate or stalemate, which is a fair question. The answer is yes. It's like asking to prove that 450g of cornflakes will all fit in a box. It's a matter of common experience that one can just shake the pack and the cornflakes settle down. There are not too many cornflakes in the box. Although it's obviously illegal, it's possible to arrange the kings and up to 34(!) white queens on the board without mate or stalemate looming. At this density, it getting a bit tight, but this thought experiment shows that when we are dealing with merely 18 queens, where moreover friendly queens can shield against enemy ones, there a vast amount of slack, and no need to worry about forced mates or stalemates. Even with 18 queens, the chessboard is a very empty box of cornflakes :-)

**Counting the collections**

Let's focus on just the White units first. How many legal White collections are there? 8,694. Here's a quick proof.

Let k be the number of visible promotions to rook, knight or bishop (i.e. officers beyond the original complement of 2 for any of these types). (For symmetry reasons, queens are dealt with in a couple of paragraphs instead.)

Let v(k) be the number of different combinations of R,N,B which achieve this.

```
v(0) = 27:
because there may be 0-2 remaining of each of R,N,B.

For k>0, v(k) = (k^2 + 15*k + 38)/2
e.g.:

v(1) = again 27:
3 ways to pick one of R,N,B to be 3;
& 0-2 possible for each of the other two types.

v(2) = 36:
27 ways to have 4,0-2,0-2;
& 9 ways to have 3,3,0-2.

```

Then the other 8-k pawns may still be Ps, or turned into Qs, or captured.

Let q be the number of visible queen promotions (i.e. queens beyond the original complement of 1).

Let u\_k(q) be the number of different combinatorial ways we can achieve this (in terms of surviving pawns, queens and captured pawns)

```
u_k(0) = 2*(9-k)
because we can have 0 to 8-k pawns, and the rest are captured,
independently we have 0 or 1 queen.

For q>0, u_k(q) = (9-k-q)

s(k) = sum(q=0,...,8-k) [u_k(q)]
= 2*(9-k) + (8-k) + (7-k) + ... 1
= (9-k)(12-k)/2.

Check:
s(8) = 2: 0-1Q
s(7) = 5: 0P,0-2Q; 1P;0-1Q
...
s(0) = 54: = 55-1

So the total number of of legal White collections is:
sum(k=0...8) [s(k)*v(k)]
= 8,694

```

All of these white collections are indeed achievable, e.g. if Black has only bare king remaining, but in fact in many other situations too: the supply/demand inequalities are not very demanding.

The next exercise involves counting for each combination of N\_w, M\_w ,A\_w how many White collections exist.

I computed the following table of numbers of collections, sorted according to the total number of pieces on the board, as shown in this table:

For each number of units from 2-32, this shows

* v\_0: the number of basic candidates without worrying about supply-demand,
* v\_1: the number who have a single fail against supply-demand,
* v\_2: the number who have a double fail against supply-demand.

To avoid double counting, the number of legal positions is computed as v\_1 - 2\*v\_2 + v\_3. My calculations match Kryukov's prior results exactly.

Note that there are no fails until one reaches 25 units. That's because with 8 captures, all candidate promotion collections can be achieved.

**An "extra credit" open question** (work in progress)

Retro enthusiasts further distinguish between the colour of squares the bishops are on, since that is an invariant. This has a major, visible impact on potential legality, is part of the essential classification for chess tablebases, and is also an aesthetic concern in composition. The corresponding term then is "non-standard officers" (queens or "tinted" bishops beyond the first; rooks or knights beyond the second). The count of missing officers is based on the same 5 types. The determination of which additional inequalities are necessary and sufficient to characterize legal collections is now substantially more complicated.

The best approach may be to first apply the adapted supply/demand inequalities. Then can ask how many extra pawn captures are required to "nudge" certain bishops to the correct tint?

A pawn capture of an officer/pawn will result in a batch of respectively 2/3 pawns all promoted on same tint squares, but it seems that for each such batch, we are free to choose the tint independently.
> 6 votes

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Tags: pawn-promotion, mathematics, pieces
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