# Question
Title: Checkmate in ω² moves with finitely many pieces
The post Checkmate in ω moves? has inspired a lot of discussion and mathematical research into positions on an infinite chessboard where white can mate in a transfinite amount of moves. The current record for a game value of a position with *finitely* many pieces is ω⋅n with an arbitrary natural number n.

Is it possible to achieve ω²?

I believe that I have found such a position, which I will share in the answer of this post - Q&A style.

# Answer
> 19 votes
# Introducing a position of game value ω² with finitely many pieces

In the following position with finitely many pieces, White has mate-in-ω² (Black to move): (For convenience, I put the position into a public Google spreadsheet so that everyone can browse it at their own leisure or copy the sheet to edit it. Alternatively, click on the pictures in this post if you want to expand them or here for a high-res image of the full position.)

The basic idea of the position is that Black will lure away the White Queen to the left by an arbitrary number of moves in the beginning. The position is constructed in such a way that

* White can never move his Queen back in a straight line because he has to keep answering constant threats by Black in very specific ways. Instead, the Queen has to be moved back very slowly in a zig-zag line, 18 squares at a time, in order to keep answering the threats. White will win only when the Queen has traveled back near the rest of the pieces.
* Inbetween every second Queen move by White, Black can move his Rook arbitrarily far away from the White King and proceed to continuously check him in such a way that White's only resort is chasing down the Black Rook with his King.

In total, these two factors lead to a game value of ω², because Black can choose in the very beginning how often he can play the check-the-White-King-from-afar game.

# Overview of the five components of the position

Now let us proceed by introducing the components of the position:

Component A is the fortress of the Black King. White has pinned two Rooks to the Black King and almost every single Black piece is completely blocked. Black can freely move exactly two pieces in the entire position during the game: his one active Rook on Aac27 and his pawn on Aac2, which exists solely to prevent stalemate & zugzwang and has no further significance. (Note: I put the letter A in front of the file letter in order to unambiguously specify that I am describing the coordinates of component A.) The Black Rook cannot threaten the White Bishops in any way or disentangle his position.

There are a few noteworthy observations about this fortress: First, the White King's movement is restricted to the top right quadrant of the board by the pinned Black Rooks. Thus, if Black were to move his free Rook north and start giving checks, then White would be unable to hide his King - he would be forced to move his King north to meet the Black Rook and push it away. Secondly, White can checkmate the Black King by capturing the highlighted Black pawn on At11 with his Queen (which is the only White piece that can freely move around the entire board, as we shall see). The numbers in the position show the path that the Queen has to take through the twisting corridor in order to reach the checkmate square: If the White Queen starts from immediately outside the corridor on the red highlighted square marked with an X (Ae17), or any other outside square on the entrance diagonal, then she will need *7 moves* to checkmate Black. Keep this number in mind as the game will critically depend on every single tempo. Finally, note that the entrance diagonal into the corridor is quite obstructed - the pawn wall to the left as well as the Northern and Southern Barriers completely block off any immediate access from the West or from the vertical files Ab through Af into the corridor.

Component B serves two functions: First, it serves the initialization of the free White Queen. We will see later that the optimal first move by Black is to move his queen as many squares as possible to the left - let's say N squares - which will lead to a position of a game value of ω⋅O(N). We will also see later that White is forced to immediately capture the Black Queen after that in order to prevent perpetual check onto his overly exposed King. After the first move, this Component is effectively frozen and will never be revisited under optimal play. The second important function of Component B is that it acts as a barrier that blocks files Ab through Af: no piece can directly move onto the entrance diagonal in Component A by moving vertically down from North.

Component C serves two functions as well: First, it is the Southern Barrier and blocks files Ab through Af from below. Secondly, it can be viewed as a ticking time bomb that Black needs to worry about. The White pawn on Cc2 can slowly move up the Cc file and capture the Black pawn on Cd17, which will allow White to slowly move up the pawn column on file Cd and release his trapped Queen on Ce3. However, this threat is very slow and White needs 30 tempi in total to release the White Queen with no way to speed this procedure up. This mechanism is significantly slower than any other threat in the position and exists solely to punish Black for sacrificing his Rook or trading it for the White Queen. Thus, this Component gives White the alternative win condition of successfully trading his Queen for the Black Rook, since Black would have no further way of preventing the inevitable release of the second White Queen. Under typical play, this Component will remain frozen for the entire game since it is far too slow. (Also note that if White ever sacrifices his Queen without compensation for some reason, Black can permanently defuse Component C after the c2 pawn has advanced 5 squares by parking his Rook on Cd6.)

Component D is a large defensive formation in which almost all pieces are frozen in place. Black has several trapped Queens on the right and White has to utilize this defensive formation in order to stop Black from liberating his Queens. (Recall that the White King is completely exposed on the top right quadrant of the board and that a roaming Black Queen will lead to draw by perpetual checks.) The Black Rook can attempt to make an incursion into the formation in order to free his Queens by moving onto the files Dm and Dq from above or Dl and Dp from below, thus threatening to move onto the red marked entrance squares with the Roman numerals I through IV (and the secondary incursion squares Iβ and IVβ). Supposing, for example, that the Black Rook is somewhere far away on the top right of the infinite chessboard (let's pick Dy45 as an example), then he can free a Black Queen with the moves 1...RDq45, 2...RDq26, 3...RxDw26, 4...RDq26, 5...Dw26, 6...Dw27, 7...QDv27, 8...QDv31 or QDv35 or QDv39, 9...Black Queen checks the White King. Thus, a Black Rook in the North or South of the chessboard *always* threatens *perpetual-in-9-moves*, pending a successful incursion onto the squares with the Roman numerals.

Now let's examine how White can answer this threat: The White Knight on Do16 (marked in orange) can defend the incursion squares II and III by jumping between the two orange squares Do16 and Dp18. Other than that function, this Knight has no freedom of movement. The White Queen can defend the incursion squares I and IV (as well as Iβ and IVβ) from afar by moving between the rows D8 and D26. Note that this suffices as a defense despite the incursion squares I and IV being defended by Black pawns, since a trade of the Queen for the Rook is a victory condition for White, as discussed above (Black can only move pawns to no effect while White slowly releases his Queen in Component C). Finally, the four White pawns on Dg7, Dh7, Dh25, Di25 (marked in blue) have the sole function of preventing an incursion by the Black Rook from the West. For instance, if the Black Rook moves to Da8, then White can defend the incursion with Dg8. Other than that function, these White pawns can make no further progress.

Note that Black is theoretically free to move the pawns on Dq9 and Dr27 forward by one square. However, this move is useless since the pawns are blocked after that move and will have achieved nothing but permanently blocking the rows D8 and D26 for Black, thus removing the threat of the incursion squares I (and Iβ) as well as IV (and IVβ).

We are now ready for an important observation: During the game, the White Queen will mostly zig-zag between rows D8 and D26 to answer threats, as we will see later. *If* the White Queen is very far away on the left of the board on one of these two rows, then it can reach the entrance diagonal of the Black King's Fortress (e.g. square Ae17) in 3 moves. (This is due to Components B and C acting as barriers. Look at the entire board configuration in order to convince yourself of this fact.) Recalling our analysis of the corridor, White thus threatens *checkmate-in-10* assuming no Black counterplay. This is a tempo disadvantage for White: he needs 10 moves to checkmate but Black can typically start giving perpetual check in 9 moves if the White Queen abandons its defensive post! However, this situation drastically changes, once the White Queen has approached the position and is within 22 squares to the left of the file Da. Then the White Queen can move *diagonally* onto the files Ac through Af *between* the two barriers and reach the entrance diagonal one move faster. Thus, White's approach is rewarded with a tempo, yielding a *checkmate-in-9* threat!

Finally, Component E is a defensive formation guarded by a lonely undefended White Bishop, the only moving piece in the position, which guards the marked pawn on Ez8, which controls a trapped Black Queen. In the position pictured above, assume that the Black Rook is on the square En26 threatening the White Bishop on En20. Assuming that White does not answer the threat, Black will free the Queen by playing 1...RxEn20 2...REn1 3...REaf1 4...REaf8 5...RxEab8 6...RxEz8 7...QEy9 8...QEs15 or QEn20 9...Black Queen checks the White King, i.e. Black again threatens *perpetual-in-9*. Thus, White is best advised to move his Bishop out of the way. The movement of the Bishop is quite restricted, in fact it can only ever visit the three unguarded squares marked in green: Ef12, En20 and Er16 (the latter two squares have a view of the important pawn). In the situation from before with the Black Rook on En26, the White Bishop should move to the right, i.e. BEr16, because moving to the left would simply result in a repetition of moves, i.e. 1.BEf12 REf26 2.BEn20 REn26, since the left green square can only be attacked from the North while the right green square can only be attacked from the South. Thus, conversely, if Black were to threaten the White Bishop from below, then the White Bishop has to move away to the left under cover, since *any* capture of the Bishop on any of the three green squares results in *perpetual-in-9*.

If the White Bishop ever sacrifices itself by going on any other square than the three green squares, then it can be immediately captured by a Black pawn or Knight. White to move will now typically have a *mate-in-10* threat, as discussed above, while Black threatens (at worst) *perpetual-in-9* via 1...REaf1 2...REaf8 3...RxEab8 4...RxEz8 5...Black Rook goes to the far right 6...QEy9 7...QEz8 8...Black Queen goes to the far right 9...Black Queen checks the White King.

Note that other than that, the position in this component is completely frozen. Any movement by the Black Knight on Ei12 is completely pointless - the Knight exists only in order to guard a few squares from the White Bishop. Moving the Knight to Eg13 or Ej14 results in immediate capture by a pawn or Bishop, if available, and the White Bishop gains a safe square on Eh14. Moving the knight to Eh14 can either be answered by capturing it with the Bishop or, in case the White Bishop is on Er16, it can be safely ignored until it is captured by the Bishop in the future, since all further moves of the Black Knight to Ef13, Ef15, Ej13, Eg16 or Ei16 can be answered by pawn captures. Thus, Black strictly improves White's position by moving the Knight.

In short, Component E is simply a switch that enables the Black Rook to move from the North of the position to the South and vice versa without losing any tempi to White.

# The opening move

What will happen in the beginning of the game? Let's examine the possible moves by Black and the best answers by White:

* *Black moves his free Rook anywhere.* At best, Black now threatens *perpetual-in-9* by one of the methods described above. White captures the Black Queen with Bfxe5 and threatens *mate-in-8* because the White Queen is already in the line of sight of the entrance diagonal. White wins almost immediately.
* *The Black Queen captures any pawn.* White can capture it back and threatens *mate-in-9* because the Queen can reach the entrance diagonal in two moves. Black to move does not threaten *perpetual-in-9* yet. White wins almost immediately.
* *The Black Queen captures the White Queen.* White answers with Bgxf5. White threatens *mate-in-9* with its newly liberated Queen. Black to move does not threaten *perpetual-in-9* yet. White wins almost immediately.
* *The Black Queen moves far West.* The Black Queen threatens *perpetual-in-1*. White has no choice but to capture it and, thus, move his Queen far away. Black then moves his Rook up an arbitrary number of squares and threatens *perpetual-in-9* in Component D. (Making a threat in Component E and crossing it does not work just yet, as we will see below, because the White Knight in Component D is in the bottom orange square.) White cannot checkmate in 9 moves by moving the Queen back and, thus, he has to answer the threat by defending it with his Queen and Knight after Black moves to file Do. (We will see below which responses for White work and which do not.)

Let us now see how a typical sequence of moves in the bulk of the game looks like:

# A typical game sequence

Assume the position above with the Black Rook on α, the White Queen on Q4, the defending White Knight on the upper orange square and the defending White Bishop on the left green square. White has just defended the Black incursion from the file Do and the Black Rook *needs* to make a new threat - since he does not threaten *perpetual-in-9* (Thus, Black passing the turn would allow White to immediately move his Queen to the right and threaten *mate-in-9*). Black moves to square β΄ and threatens the White Bishop. The White Bishop has to move to the central green square. Black moves to square β and the White Bishop moves the right green square. The Black Rook cannot threaten the Bishop anymore and moves his Rook to square γ (Any move in another direction would just waste a tempo). Now Black threatens an incursion from the file Dn in two moves and White (needing at least two moves to defend this threat) thus moves his Queen to square Q3. Black proceeds by moving his Rook to the square δ, which White has to answer by moving his knight to the lower orange square - White has defended the threat just in time. Now Black moves his Rook to γ΄, the White Bishop has to run to the central green square, Black responds by moving to γ, White moves his Bishop to the left green square, and then, finally the Black Rook moves up in the direction of square β, to which White responds by moving his Queen to Q2. Here, the transfinite ω has come into play! Namely, the "new" square β can be as arbitrarily far North from the White King as Black wishes! Now Black can start giving checks to the White King from above and the White King is forced to approach the Black Rook - this might take *many* moves. Before the White King reaches the Black Rook, Black moves his Rook to square α and White has to move his Knight to the upper orange square in defense - he has just made it in time again. This closes the loop and the position is exactly the same as before, except that the White Queen is now on Q2 instead of Q4, i.e. it has moved 36 squares to the right in "ω+8" moves. This loop continues until the White Queen reaches Q1, which is sufficiently near to the Barriers in order to allow the White Queen to dip between the two Barriers, which improves White's imminent threat from *mate-in-10* to *mate-in-9*. As soon as the next position is reached where Black only threatens *perpetual-in-9*, White can ignore the threat and proceed to checkmate Black.

# Strategic summary of the main line

After the first move, White and Black find themselves in a constant battle of tempi. White is threatening *mate-in-10* (assuming no black counterplay) for the entire duration of the game. This forces Black to *only* make threats that are faster than 10 moves. Black can indeed quite successfully keep playing for a *very* long time in such a way that his every single move both threatens *perpetual-in-9* and forces an *immediate* response by White to prevent this. Neither can Black ever find a strategy that breaks through the defense of White nor can White immediately force a position of *mate-in-9* which would be fast enough to beat Black - that is until the White Queen is within ~22 squares of Component D, when the balance turns in favor of White and he does in fact reach a position of *mate-in-9*, which ends the game. It turns out that this best defense by Black has a game value of exactly ω².

# Remarks, deviations from the strategy above and their refutations

* If Black manages to ever successfully release a Black Queen and start checking the White King, then White has no way of winning anymore. Not even a Queen trade and Component C can still salvage the position, since Component C is easily disarmed by a Black Rook, as stated above.
* Black gains no advantage by threatening the secondary incursion squares Iβ and IVβ (Dl8 and Dm26) since this threat is strictly weaker than the threats on the files Dp and Dq.
* If Black ever moves his Rook to the far left or far right, then White can immediately move his Queen right to Component D in a straight line because such a move by Black is no threat. The blue-colored pawns in Component D prevent any incursion from the left in a single move, if needed - thus Black has created no new threat and just wasted a move. If Black moves his Rook onto rows D8 or D26, White defends with a blue pawn, threatens *mate-in-9* and will win very shortly. Similarly, Black capturing the Eab8 pawn without having removed the defending Bishop is pointless since it wastes 3 tempi and White needs 1 tempo at most to guard the crucial Ez8 pawn with his Bishop. All in all, Black cannot ever capture any non-significant White pawn or move his Knight in Component E since this wastes too much time.
* Black cannot go through Component E twice in a row without threatening Component D, since then the White Knight would be on the same side of Component E as the Black Rook after the second time. In this case, White could use the tempo, where the Knight would normally have to move, to instead move the Queen as far right as he wants while still defending against the threat in D.
* A long horizontal move by the White Queen to the right at any point in time results in a draw because Black makes a new *perpetual-in-9*-threat every single move that needs to be answered, either by moving the Bishop or Knight or by changing the row of the Queen. Thus, White has wasted a critical move and cannot answer the next Black threat or incursion attempt like in the main line.
* A long diagonal move by the White Queen to the files Dp or Dq as a defense against the Black Rook having reached squares β or γ is pointless, because the Black Rook can just immediately threaten the secondary incursion squares Iβ and IVβ, and the White Queen has no choice but to revert its last move. (These secondary incursion squares exist solely for this reason.) Note that the White Queen cannot defend the secondary incursion squares from Dp8 or Dq26 since these squares are guarded by Black pawns (which exist solely for that reason). Similarly, a long vertical move by the White Queen can also be dealt with in the same way since White cannot ever prevent Black from threatening both the primary and the secondary incursion squares.
* A long diagonal move by the White Queen to the file En in order to defend the White Bishop is pointless because the Black Rook can just move back to α or δ respectively, threaten an incursion into Component D again, and force the White Queen to undo its last move.
* White cannot ever leave a threat to his Bishop in Component E unanswered because this would lead to a draw, since the White Queen cannot defend the vulnerable White pawn on Ez8. Without the defending Bishop in Component E, a Black Rook on the far right of row E8 threatens (at worst) *perpetual-in-7* in Component E and *perpetual-in-10* in Component D. The Black Rook is free to move North and South, making threats to Components D and E that cannot all be covered simultaneously.
* **Important:** The Black Rook needs to be careful to choose its distant squares α, β, γ and δ in such a way that the White Queen cannot ever interfere with the Rook diagonally. This is always possible for Black since he can move his Rook sufficiently farther away vertically than double the horizontal distance to the Queen.
* White could try to move his King in such a way that the White Queen can at some point block a check by the Black Rook from the North by moving directly in front of the King, but this only leads to a repetition of moves since Black can move his Rook back to square α and repeat his last threat. Thus, the White King actually has to hunt down the Black Rook.
* When the White Queen finally attempts to checkmate Black in the end, the White King needs to be careful to not stand on certain diagonals and files, namely those that release the Queens out of Components D and E, else Black will have a threat of *perpetual-in-8*. This is possible for White since he has enough freedom of movement with his King to stay away from these critical lines.
* White cannot prevent the immediate check from the Black Queen in the 9th move (after leaving a *perpetual-in-9* threat unanswered) solely by moving his King to a suitable position on the top right quadrant, because both Components D and E give the respective Black Queens several exits that are spaced sufficiently far apart. (For instance, in component D, the Black Queen can choose between the squares Dv31, Dv35 and Dv39 on the move before initiating perpetual checks.) The Black Queen will always be able to threaten the undefended White King vertically or horizontally.
* The Black and White pawn to the left of Component B exist solely to prevent the White Queen moving horizontally back onto file Dq after the initial capture and Black Rook movement. (In this deviation, the Black Rook will threaten the incursion square Iβ from above and the White Queen is unable to defend it in time because of being blocked by pawns.)

**Remark:** This same position with the Black Rook shifted k squares to the right has a game value of ω²+k, since Black can start by giving k checks to the White King. As long as the White King is careful not to go above row A29 during this chase, the position is qualitatively the same and Black will not gain any advantage with these checks.

*Disclosure: I have also posted this analysis as an answer to the original post "Checkmate in ω moves?".*

*Edit: Further work has led me to revisit this position and slightly rework the Components, however without changing the idea of the position or the main line. My goal was to make the position more convincing and clear up some problematic aspects of the previous position, like unforeseen piece sacrifices and deviations from the main line.*

---
Tags: problems, checkmate, chess-variants, mathematics
---


# Question
Title: Program to merge chess opening polyglot database files with recalculation of weights
I have been trying to merge polyglot chess opening databases. When merging databases with existing programs, if any move in a position already exist in the first file, new moves from same position will not be added from the next file.

Here is the problem: When two books (in bin-format) are merged with polyglot, it's expected that lines from both of them can be found in the new combined/merged one. This is not the case: the contents of the second entry are omitted:

pgn1:

```
[Event "?"]
[Site "?"]
[Date "2021.01.01"]
[Number "1"]
[White "?"]
[Black "?"]
[Result "1/2-1/2"]
[ECO "B74"]
[PlyCount "12"]

1. e4 c5 1/2-1/2

```

pgn2:

```
[Event "?"]
[Site "?"]
[Date "2021.01.01"]
[Number "1"]
[White "?"]
[Black "?"]
[Result "1/2-1/2"]
[ECO "A00"]
[PlyCount "12"]

1. g3 e5  1/2-1/2

```

After doing:

```
polyglot make-book -pgn 1.pgn -min-game 1 -max-ply 12 -bin 1.bin

polyglot make-book -pgn 2.pgn -min-game 1 -max-ply 12 -bin 2.bin

polyglot merge-book -in1 1.bin -in2 2.bin -out combined.bin

```

the `g3 e5` entry gets scraped.

For reference, the above definition of the problem was described here: https://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg1798406.html

This is something I have found really annoying for a very long time. After years of frustration that there was no program that could properly merge chess polyglot database files with recalculation of weights, I eventually decided to learn how to make a program that could do that.

So, now I have written a program to merge chess opening polyglot database files with recalculation of weights and it solves this problem. I call it merge\_polyglot.

But I don´t really have any clue what to do with it. Would others find this useful? Where would I post this program to make it available for other chess enthusiasts?

# Answer
> 1 votes
You may use the more versatile subcommand `jja merge` of the tool jja:

```
⇒  jja merge -h
Merge two opening books

Usage: jja merge [OPTIONS] --input1 <input-file-1> --input2 <input-file-2> --output <output-file>

Options:
  -1, --input1 <input-file-1>
          First opening book
      --porcelain[=<FORMAT>]
          Give the output in an easy-to-parse format for scripts [default: auto] [possible values: auto, csv]
  -2, --input2 <input-file-2>
          Second opening book
  -v, --verbose...
          Run verbosely, may be specified multiple times [env: JJA_VERBOSITY=]
  -o, --output <output-file>
          Path to the output chess file
  -T, --threads <threads>
          Specify maximum number of threads [env: JJA_NPROC=] [default: 4]
  -s, --strategy <merge-strategy>
          Merge strategy [default: sum] [possible values: avg, max, min, ours, sum, wavg]
  -w, --weight1 <merge-book1-weight>
          Book 1 weight for merge strategy weighted average, aka `wavg'
  -W, --weight2 <merge-book2-weight>
          Book 2 weight for merge strategy weighted average, aka `wavg'
  -c, --weight-cutoff <merge-weight-cutoff>
          Moves less than this weight will not be included in the book
  -h, --help
          Print help
  -V, --version
          Print version

```

To solve your problem you should use a merge strategy which suits your needs. If you want to keep both entries you would go for either `avg`, `sum`, or `wavg`, `max` and `min` which states how the weight field should be updated for entries with same moves with averaging them, summing them and weighted averaging, using the maximum weight, and using the minimum weight being five options.

If you want to keep a single field, then you should use `ours` strategy which keeps entries in the first book intact when both book have the same position. I use this very often when I merge a small book with my own openings over a huge book generated from a database of lichess games so I get to use the information from lichess database whilst still having my own preferred moves selected for the positions I want. Another common option I use is `--weight-cutoff` with which I can get rid off very weak moves in the opening book.

Finally I should admit I am the author of jja so this is in-part self-promotion for which I apologize.

---
Tags: software, polyglot
---


# Question
Title: Checkmate with two bishops of same colour
Is it possible to checkmate King with two bishops of same colour in the endgame?.

Is it possible in Chess to get this position in reality?

Position:

King with Two bishops of same colour V/S King.

# Answer
> 3 votes
No, there is **no possible checkmate** with 2 (or more) same-coloured bishops against a bare king. The game is drawn immediately.

Indeed, if White has light-squared bishops then:

* when the black king stand on a dark square, it cannot be attacked
* when the black king stand on a light square, it can be attacked but there are at least two adjacent dark squares (more if it isn't in a corner), of which the white king can only deny one : Black is in check but not in checkmate and the king escapes.

For example, in the position (the most White can get) White: Kc2, Bf4, Bc5 / Black Ka1 :

1.Be5 is check but a2 is not controlled: 1...Ka2 and the game is a draw.

If you add a Black pawn, a checkmate pattern become possible. However, it takes 5 bishops (!) in this study by Alexei Troitsky (thanks to @HaukeReddmann for the reference) for White to be able to force a checkmate !

---
Tags: endgame, bishops, kings
---


# Question
Title: How to calculate the FIDE Percentage Expectancy Table
Section 8 of the FIDE Rating Regulations provides the following table

I understand that dp=800 and dp=-800 are arbitary caps at the top and bottom of the table.

However, in relation to the other scores, what's the formula for the conversion of p into dp, and vice-versa?

As noted in the comments, the regular Elo formula almost works but does not quite work. Does anyone know what the formula is for the adjustment made in the tails?

# Answer
> 8 votes
It's basically just table 8.1a with the columns switched. E.g. the entry in table 8.1b with rating difference 92-98 and expected score (for the higher rated player) of .63, corresponds with the entry (.63, 95) in table 8.1a.

*That* table is based on the expected score formula mentioned here:

> If Player A has a rating of RA and Player B a rating of RB, the exact formula (using the logistic curve) for the expected score of Player A is
>
> EA = 1 / (1 + 10 (RB \- RA) / 400)

but it's also possible to directly generate table 8.1b from this formula. For example, a rating difference of 92 points (in A's favor) leads to EA = 0.6294.

The inverse formula, calculating the rating difference which corresponds to a certain expected score, is RB \- RA = 400 log10(1 / EA \- 1).

# Answer
> 2 votes
As stated in 12.1 the formula above gives a close approximation to tables 8.1a and 8.1b. However it does not explain the precise construction of the table. Take fore example Rb-Ra = -736. According to the table 8.1b, the resulting expectation equals 100%. But according to the formula, the expectation is 98,57%.

# Answer
> 1 votes
Table 8.1a is a mirror image of:

The Percentage Expectancy Table (A.E. Elo *The Rating of Chess Players*, 2.11)

```
   D        P    |    D       P    |    D        P
Rtg.Dif   H   L  | Rtg Dif  H   L  | Rtg Dif   H   L
  0-3    .50 .50 | 122-129 .67 .33 | 279-290  .84 .16
  4-10   .51 .49 | 130-137 .68 .32 | 291-302  .85 .15
 11-17   .52 .48 | 138-145 .69 .31 | 303-315  .86 .14
 18-25   .53 .47 | 146-153 .70 .30 | 316-328  .87 .13

 26-32   .54 .46 | 154-162 .71 .29 | 329-344  .88 .12
 33-39   .55 .45 | 163-170 .72 .28 | 345-357  .89 .11
 40-46   .56 .44 | 171-179 .73 .27 | 358-374  .90 .10
 47-53   .57 .43 | 180-188 .74 .26 | 375-391  .91 .09

 54-61   .58 .42 | 189-197 .75 .25 | 392-411  .92 .08
 62-68   .59 .41 | 198-206 .76 .24 | 412-432  .93 .07
 69-76   .60 .40 | 207-215 .77 .23 | 433-456  .94 .06
 77-83   .61 .39 | 216-225 .78 .22 | 457-484  .95 .05

 84-91   .62 .38 | 226-235 .79 .21 | 485-517  .96 .04
 92-98   .63 .37 | 236-245 .80 .20 | 518-559  .97 .03
 99-106  .64 .36 | 246-256 .81 .19 | 560-619  .98 .02
 107-113 .65 .35 | 257-267 .82 .18 | 620-735  .99 .01
 114-121 .66 .34 | 268-278 .83 .17 | over735 1.00 .00

```

**How to reproduce this table?**

Since the normal curve flattens, one would expect that the number of rating differences does not decrease. However, there is a discontinuity at D = 345-357, P = 89%. This suggests that the table may contain irregularities

```
Rtg Dif Range
279 290 11
291 302 11
303 315 12
316 328 12
329 344 15
345 357 12 <---
358 374 16
375 391 16
392 411 19

```

Construction of the table is most likely:

* Let *sigma = 200 * (10 / 7)*, where *10 / 7* is an approximation for *sqrt(2)*. Reference: A.E. Elo, *Theory of Rating Systems*, privately printed monograph, 1966.
* Convert 0, 20, 40, 60, etc. into Z scores: 0, 0.07, 0.14, 0.21, etc. using Z = D / sigma. The corresponding probabilities can be found in the "Standard normal table", which gives 0.5000, 0.5040, 0.5080, 0.5120. Elo could have used table X, p.91 from Garrett, H.E. *Statistics in Psychology and Education*. David McKay , New York , 1966.
* Intermediate values can be derived by linear interpolation.

The following differences exist between this calculation (in R base) and the Elo table:

```
D     <- c(343, 344, 358, 392)      # import from Elo table
P     <- c(.88, .88, .88, .92)      # import from Elo table
dD    <- 20L                        # increment    in D = 0, 20, 40, etc.
sd    <- 200L * (10L / 7L)          # standard deviation.
dZ    <- 0.07                       # dD / sd, increment in Z.
Z0    <- trunc(D / dD) * dD / sd    # index in Z table begin.
Z1    <- round(Z0 + dZ, 2)          # index in Z table end.
PZ0   <- round(pnorm(Z0), 4)        # P before.
PZ1   <- round(pnorm(Z1), 4)        # P after.

ix    <- D %% dD                    # index 0 - 20.
Pstep <- (PZ1 - PZ0) / dD           # interpolation step.

P4    <- PZ0 + ix * Pstep           # intermediate percentage.
P2    <- round(P4 + 5E-5 + 1E-6, 2) # rounded up to 4 decimals then 2.
Diff  <- round(P2 - P, 15)          # Diff with Elo table.
cbind(D=D, P=P, Diff=Diff, P2=P2, P4=P4, Pstep=Pstep, ix=ix, PZ1=PZ1, PZ0=PZ0, Z1=Z1, Z0=Z0)

```

Output.

```
##        D    P  Diff   P2      P4   Pstep ix    PZ1    PZ0   Z1   Z0
## [1,] 343 0.88  0.01 0.89 0.88498 0.00066  3 0.8962 0.8830 1.26 1.19
## [2,] 344 0.88  0.01 0.89 0.88564 0.00066  4 0.8962 0.8830 1.26 1.19
## [3,] 358 0.88  0.01 0.89 0.89488 0.00066 18 0.8962 0.8830 1.26 1.19
## [4,] 392 0.92 -0.01 0.91 0.91480 0.00055 12 0.9192 0.9082 1.40 1.33

```

Elo probably made a few clerical errors during the laborious manual calculation.

```
##      D    P   Diff   P2      P4    Pstep  ix    PZ1     PZ0    Z1   Z0
##     343 0.88     0 0.88 0.88416 0.000720*  3 0.8962  0.8820* 1.26 1.19
##     344 0.88     0 0.88 0.88488 0.000720*  4 0.8962  0.8820* 1.26 1.19
##     358 0.90     0 0.90 0.89496 0.000720* 18 0.8962  0.8820* 1.26 1.19
##     392 0.92     0 0.92 0.91498 0.000565  12 0.9195* 0.9082  1.40 1.33

```

---
Tags: rating, elo
---


# Question
Title: How do convert/parse/extract data from a PGN into a spreadsheet/google sheet/excel file?
Sequel to this question: Live statistics chess960 from chess.com?

So suppose I go to like

https://api.chess.com/pub/player/gmwso/games/2020/12

or

https://api.chess.com/pub/player/gmwso/games/2020/12/pgn

there's gonna be a bunch of stuff like say

```
[UTCDate "2018.01.03"]
[WhiteElo "2706"]
[BlackElo "2940"]

```

How do I get this data into a spreadsheet like column 1 is all the dates, column 2 is the corresponding white elo, column 3 black elo, col4 white username and col5 black username?

---

Update 2: Fixed now. see the 'json' vs the 'preformed'. WOW.

Update 1: It appears Mike Steelson has an answer here, where the code is given as

```
=arrayformula( regexextract(split( substitute(substitute(substitute(getDataJSON(A1;"/games";"/pgn");"[";"");"]";"");"""";"") ;char(10));"\s.*") )

```

with an example given here

https://docs.google.com/spreadsheets/d/1MX1o5qdy0K3gTMzbimUV3SmFf-0XPCSJ8Vz4IjI-8Ak/copy

It appears there's a problem when it gets to the case of chess960 only. Consider for example this player: Replacing 'gmwso' with the player's username will yield a weird output. i imagine the output will be messier for mixed chess960 and chess.

# Answer
> 3 votes
> How do I get this data into a spreadsheet like column 1 is all the dates, column 2 is the corresponding white elo, column 3 black elo, col4 white username and col5 black username?

From the .pgn file downloaded at

https://api.chess.com/pub/player/gmwso/games/2020/12/pgn

I have created a file called chess\_games.xlsx and I have inserted the five values you are asking using a python2 script. You need to install chess and openpyxl libraries with pip. The .pgn file is read as a long string.

```
import pgn
import openpyxl
import os

pgn_text = open('ChessCom_gmwso_202012.pgn').read()

dates = []
welo = []
belo = []
white = []
black = []

whiteLong = []
blackLong = []

def getValues(file):
    test_str = file
    test_date = "[Date"
    res1 = [i for i in range(len(test_str)) if test_str.startswith(test_date, i)]
    test_welo = "[WhiteElo"
    res2 = [i for i in range(len(test_str)) if test_str.startswith(test_welo, i)]
    test_belo = "[BlackElo"
    res3 = [i for i in range(len(test_str)) if test_str.startswith(test_belo, i)]
    test_white = "[White "
    res4 = [i for i in range(len(test_str)) if test_str.startswith(test_white, i)]
    test_black = "[Black "
    res5 = [i for i in range(len(test_str)) if test_str.startswith(test_black, i)]
    for i in res1:
    dates.append(test_str[i+7:i+17])
    for i in res2:
        welo.append(test_str[i+11:i+15])
    for i in res3:
        belo.append(test_str[i+11:i+15])
    for i in res4:
        whiteLong.append(test_str[i+8:i+43]) //The max length of a nickname in chess.com is 35 characters
    for i in res5:
        blackLong.append(test_str[i+8:i+43])
    for value in whiteLong:
        posClose = value.find("]")
        white.append(value[0:posClose-1])
    for value in blackLong:
        posClose = value.find("]")
        black.append(value[0:posClose-1])

def generateExcel(dates,welo,belo,white,black):
    file = 'chess_games.xlsx'
    if os.path.isfile(file):
        wb = openpyxl.load_workbook(filename=file)
    else:
        wb = openpyxl.Workbook()
    ws = wb["chess_games"]
    for k in range (len(dates)):
        ws['A'+str(k+1)] = dates[k]
    for k in range (len(welo)):
        ws['B'+str(k+1)] = welo[k]
    for k in range (len(belo)):
        ws['C'+str(k+1)] = belo[k]
    for k in range (len(white)):
        ws['D'+str(k+1)] = white[k]
    for k in range (len(black)):
        ws['E'+str(k+1)] = black[k]
    wb.save(file)

getValues(pgn_text)
generateExcel(dates,welo,belo,white,black)

```

Download the output .xlsx file

# Answer
> 2 votes
First, worth noting that this question has nothing to do with chess. It is a programming question and a simple one at that.

The answer is very simple. Write a program to read the files and parse them. The pseudo-code looks something like this:

Read the file
For each line

1. find and extract any keywords like "WhiteELO", "UTCDate", etc.
2. If there is no keyword then throw the line away (or do something else if you need to)
3. If there is a keyword then extract and store the associated data

Once you have processed all the lines of the game in the pgn then write a formatted line to your output file.

Note that for spreadsheet-readable files you can use something like ";" (semicolon) as the field delimiter. Probably better than "," (comma) since the title and player name fields are likely to contain commas.

Note that there was nothing whatsoever to do with chess in that answer. It was all simple data processing.

# Answer
> 1 votes
Update 2: Fixed now. see the 'json' vs the 'preformed'. WOW.

Update 1: It appears Mike Steelson has an answer here, where the code is given as

```
=arrayformula( regexextract(split( substitute(substitute(substitute(getDataJSON(A1;"/games";"/pgn");"[";"");"]";"");"""";"") ;char(10));"\s.*") )

```

with an example given here

https://docs.google.com/spreadsheets/d/1MX1o5qdy0K3gTMzbimUV3SmFf-0XPCSJ8Vz4IjI-8Ak/copy

It appears there's a problem when it gets to the case of chess960 only. Consider for example this player: Replacing 'gmwso' with the player's username will yield a weird output. i imagine the output will be messier for mixed chess960 and chess.

# Answer
> 0 votes
I avoided having to write a programming script to convert a PGN games file into a spreadsheet, but I used a word processing application instead.

The WP app needs to support regular expressions (regex), which allow you to use variables as well as the usual literals. Basically, this is activated by setting a checkbox in the Find/Replace dialog(s), but you need to use special characters to specify how you want the text manipulated. (The helpfile on "regex" explains how, with examples.)

The key is that each variable in a PGN game header stands on its own line. To concatenate them all for use by a spreadsheet, you need to convert the paragraph separator characters, which I'll call \[Para\] characters, into \[Tab\] characters.

But first, knowing that all PGN games are separated by a blank line indicates there are two para characters separating them. This makes the \[Para\] chars ambiguous, except for the pairing characteristic when they're used for game separation. You want the games on separate rows in your spreadsheet, so you need to preserve this game separation info and restore it once the concatenation is complete.

So, first I copied (or opened) the PGN file in(to) MS Word.

Then I regex-replaced all the double-para characters with a special-character pair I reserved for that purpose: "&&". That's the delimiter between games.

(Note: As you manipulate the file in Word, it will immediately start looking weird. Ignore that, and just execute the steps.)

Next, I regex-replaced all the "\]\[Para\]" End-of-PGN-Field character pairs with a special-character pair I reserved for that purpose: "\]%". The "\]" is just a target-finder; it specifies that only the lines ending in a "\]" are to be concatenated. The "%" becomes the delimiter between the PGN fields, and between the last field and the start of the game score.

Next, you have to concatenate the moves, which have been arbitrarily split by the PGN file creation software so that they're human-readable using a simple text processor, like Notepad.

To do this, I regex-replaced all remaining \[Para\] chars with space " " chars. This concatenates the game scores, with at least one space between the end of one line and the beginning of the next from the PGN file. Note that this has no effect on the PGN header fields or the game separations; those were already converted to special characters to prevent them from being affected by this step.

Next I regex-replaced the "%" characters with "\[Tab\]" characters so the PGN fields will load into separate columns in the spreadsheet when the time comes.

Finally, I regex-replaced the "&&" character pairs with \[Para\] chars so that each game would be on its own row in the spreadsheet.

Finally, I selected all (you can use "Select-All", instead of trying to drag-select over sometimes 100's of pages, but even that can be done by placing the cursor at the start of the text \[Ctrl\]-\[End\]) of the text from the document, opened a fresh spreadsheet, and pasted the text.

A few caveats:

1. If you find that some of the PGN games have one set of PGN header fields, and some of them have a different set (this shouldn't happen, but might if your PGN file creator adds uncommon fields only for the games that came with that data, and omits them for others), then you can easily detect the disparities by just looking for misalignments in one of the last PGN file columns in the spreadsheet. If this affects only a small number of rows, you can generally correct it with some manual copy-pasta work in the spreadsheet to realign the fields. I always dropped any PGN field that only a few games had.

Before you undertake the manual process, assess the magnitude of the effort. How many rows are non-conforming to the standard content of the majority of the games? If it's a lot, and you don't need the unusual fields, it may be more efficient to just repeat the text file conversion process, but precede it by first removing all of these non-conforming fields and their data. Again, you can use a regex-replace to specify a starting "\[", the name of the field plus a \[wildcard\] character to specify all of the non-essential text, as well as a "\]", and then just replace them all with nothing.

Some may observe that if we had known this would be a problem before beginning the first conversion cycle, we could have saved that effort. That's true, but it turns out the most reliable way to find the anomalies is to produce a pilot version of the spreadsheet, and look for the misalignments of PGN fields caused by the interjection of the unusual fields' data in the anomalous rows. This is comprehensive, 100% effective at avoiding false positives and false negatives, and fairly easy. In the conversion process itself, once a step has been executed and verified to operate correctly, can be easily repeated using shortcuts like "Last Used" dropdown box selections in the Regex dialog box, or even automated with simple macros or one master macro (though in that case we're back to programming).

2. Sometimes there are anomalies in PGN game files that cause a game (or even swathes of them) not to be recognized by a chess reader. (I'll leave to you whether it's worth pursuing and addressing how they occurred.) Therefore, you should always get a count of the PGN games that are *supposed* to be in the file by counting the number of occurrences of a telltale, standard PGN field (I like to use the "White" field). To get the count, load (a copy of) the PGN file into your word processor and do a replace of "White" with "White". The file will be identical, but the word processor will report the number of replacements.

Then load the file into a chess reader, and check the number of games it reports in the file. If the numbers don't match (the reader's count cannot be higher, but it can be lower), I always isolate the games that the chess reader can't read and try to recover them. Most of the time, it's just a matter of correcting some character anomaly, a missing field delimiter "\[" or "\]", or (rarely) a missing required PGN field.

If this problem exists, it may cause the reader to stumble and be unable to read several perfectly intact games after the offending game; don't assume that subsequent "unreadable" games all have problems. Often, fixing the first in the set and then trying again magically makes all of them readable.

3. PGN readers are (by the specification in the standard) very tolerant of lots of sloppiness, so they ignore most disparities between one game and the next, including the order of fields. If you get all of the PGN games in a file from one source, then such disparities shouldn't appear at all. But if you concatenate games from different sources (which I highly discourage, for this reason), they are likely to show up. Then, trying to get the data from multiple sources to align in the right spreadsheet columns for all of the rows can be a real exercise.

Better to load PGN files from different sources into separate spreadsheet tabs, and then merge them later after any column inconsistencies between them have been identified and sorted out.

Why do this analysis prep work at all? I've used it to find games that met several criteria:

* Upsets, based on the underdog's ELO deficit vs their opponent
* Miniatures (games with decisive results in under \[game-length-limit\] moves.)

but the ability to sort, filter and calculate based on the PGN fields alone has made it worthwhile in my research.

---
Tags: chess-variants, programming, database, statistics, chess960
---


# Question
Title: Can electronic music really have a positive effect on online chess?
I ask this question because of the public figures I have seen playing electronic music in the background, among them the runner-up Ian Nepomniachtchi. I cannot rely on my experiences, as they may be conditioned.

# Answer
> 5 votes
Surprisingly, the answer is yes. Listening to music can increase blood flow to the brain. Musicians are also known to have more gray matter in the frontal cortex which can form more complex neural networks.

To put it simply, music activates your memory, and memory is the number 1 tool when playing chess.

Obviously most people prefer silence when playing but that’s not to say that it couldn’t work.

Here is a scientific article on the matter: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776393/

---
Tags: strategy, training, psychology, study, online
---


title: Arbiter talking to player

text:
# Question
Title: Arbiter talking to player
So I've got a question regarding if an arbiter can talk to a player in this situation : My clock was running and I was thinking about the next move that I should make. I was already 10 minutes into thinking when this arbiter (international arbiter) told me while I was thinking and my clock running that my water bottle had to be on the floor. The bottle was on the table and far away from touching the board if it was knocked.

Can arbiters interrupt you to do this while it your turn?

# Answer
> 4 votes
> Can arbiters interrupt you to do this while it your turn?

Of course!

Article 12 of the FIDE Laws of Chess defines the role of the arbiter. In particular it says this:

> 12.2 The arbiter shall: ... 12.2.3 ensure that a good playing environment is maintained,

Having water bottles on the table was not conducive to a good playing environment in the view of the arbiter.

> The bottle was on the table and far away from touching the board if it was knocked

Was the bottle glued or nailed to the table so that it couldn't move? Of course not! You had it on the table with the intention of picking it up, drinking from it and then putting it back down on the table. Where it is now is not necessarily where it is going to be later. In particular, later might be when both players are in time trouble, trying to move fast and hit the clocks fast and the bottle can get knocked hard and fly into the board causing havoc when neither player has much time and both players are stressed. Don't put tall, unstable objects on the table.

---
Tags: etiquette, arbiters
---


# Question
Title: Why is it better to control a vertical/horizontal than diagonal?
I'm trying to truly understand why Rooks are more valuable than Bishops. Yes, they control more squares. But *why*?

I understand that a rook forms a line that pieces cannot pass through, and this is related to the fact that it controls squares of multiple colors. A diagonal does not block a piece in the same way.

But I just cannot wrap my head around why controlling all squares in a cardinal direction is any better than controlling all squares in an ordinal direction. Does anybody have a mathematical or logical explanation for this? Why does controlling squares cardinally result in more total squares controlled than doing so ordinally?

# Answer
The other answers here are great. Inspired by them, I came up with a mathematical reason.

**Basically, diagonal walls have holes because bishops are limited to half the squares.**

Define a move as a vector: `<+xpos, +ypos>`.

Any Rook move has the following vector basis: `{<1,0>, <0,1>, <-1,0>, <0,-1>}`

Any Bishop has the following vector basis: `{<1,1>, <-1,-1> <-1,1>, <1,-1>}`

When a Bishop moves, `sum(Δx, Δy)` must be even. Therefore, it must move to a square of the same color. When a rook moves, `sum(Δx, Δy)` may be even or odd, so it can move to a square of either color.

As an extension, for a knight, `sum(Δx, Δy)` must be odd. Therefore, it must move to a square of a different color.

**The reason that bishops can only reach half the board is because they are limited to moves over an even amount of squares, while rooks can move over an even or an odd amount of squares**.

This means that bishops lack the same blocking capabilities as rooks. Also, they see fewer squares (7-13 vs 14), for the same reason.
> 1 votes

# Answer
I'm not sure exactly what question you're asking, but here are a few ideas related to why rooks might be stronger than bishops:

* Bishops are easier to block with pawns. If a bishop sits on a nice open diagonal, it's quite likely that the opponent can adjust their pawn structure to block it. On the other hand, if a rook sits on a nice open file, then mostly the file stays open.
* On an empty board, from any square a rook covers 14 other squares. A bishop covers somewhere between 7 and 13. Put another way, some diagonals are very short, while all ranks and files are long.
* As you mention: although a bishop can cover quite a few squares at a time, there are half the squares on the board that it can *never* attack. The rook is more flexible and there is no square it can't attack. For example, on an open board it's much easier for a rook to harass a bishop than for a bishop to harass a rook (although in a more cramped position, a bishop may be able to keep a rook off particular important squares).
* Rook and king alone can mate, unlike bishop and king. Similarly, a rook can deliver back-rank mates.
* A rook can attack a pawn in such a way that the pawn can't move out of the attack. A bishop can't (unless the pawn is blocked).
> 26 votes

# Answer
I am answering the mathematically-oriented question why are rooks controlling more squares (the chess question of why are rooks better pieces is well-answered here: Why is the rook worth 5 points while the bishop is only worth 3?)

Rook on position (X,Y) can move to the left: X-1 + top: Y-1 + right: 8-X + bottom: 8-Y. Sum this up and you get 14 tiles it can move to. No matter where the rook is. On a different rectangular board you get N and M instead of 8s, leading to N+M-2 squares it can move to. This is because movement in one direction is independent on the other direction and all ranks and files are as long.

Take bishop on the same position (X,Y). Going left-up, it can move by min(X-1, Y-1). Likewise for other directions. Those minimums are because bishop reaches the end of either row or column first and cannot move further - limiting bishop's mobility. In the optimal case for bishop in the center of an odd-sized square board, it can move to as many spots as a rook can (2N-2); however, if the bishop is in a corner, it can only move to N-1 squares.

But you can construct a board (diamond-shaped) where number of moves for bishop is constant while number of possible rook squares changes (but is as high or higher than number of bishop moves). You can also make boards where a rook reaches fewer squares than a bishop does in a single move (eg a tri-diagonal strip starting on A1 and go up to H8 together with both side diagonals) - so, even though rook reaches all tiles, bishop moves faster over that board.
> 14 votes

# Answer
Apart from the obvious advantages of the rook that you also mentioned (according to the rules of chess) I think your question boils down to this:

*Why is the bishop vs. rook on a chessboard different from vertical + horizontal lines vs. diagonal directions in an open (infinite) plane?*

I'm trying to answer this here, attempting to clarify exactly where those advantages come from (mathematically? geometrically?).

## Bounds of the board

The chess board is a **square** board, not an infinite plane, so the directions matter. The rook has an advantage because the directions it can move in coincide with the square's sides.

The rook cannot be stuck in a corner, a bishop can, so that one of the directions is blocked and it can only move in one direction. This means that while both pieces can reach any of their possible destinations in 2 moves, the rook can decide which of the 2 moves it takes first, but a 'stuck' bishop in a corner can't.

## Grid

The chessboard is not just a square, but a **grid** of squares (so you could say it is discrete). If you think about it, the previous point about the bounds of the board holds even if there is no grid (if any piece could move an arbitrarily small distance), but in addition, the bishop also loses half of the board, and that is a consequence of the grid.
> 6 votes

# Answer
> But I just cannot wrap my head around why controlling all squares in a cardinal direction is any better than controlling all squares in an ordinal direction.

We can picture a world where they actually are the same. Imagine playing chess on a board from the game of Hex. Here, a king can only move to the six adjacent tiles (green). A "rank" and a "diagonal" are the same. The rook and bishop both block the king.

But now we change the rules to let the king jump two squares up and to the left, or two squares down and to the right. Just like in chess, the king has 8 squares to go to. And just like in chess, the poor bishop can be bypassed.

So this is how we get a chess board: we squish the Hex board into a square, and we say that a tile is adjacent to the tile that is up+left of it, as well as the tile down+right of it. We make a new diagonal for the up+left and down+right direction, pictured below in pink. It has the same "bishop" problem as the opposite diagonal: the king can hop over it.

Two key points:

1. Because of where we added the new green dots, a rook can control up to three squares adjacent to the king, but a bishop can only ever control two.
2. On a chessboard, the king can only move one over by one rank or file at a time, but can move *two* diagonals at a time. (On a chessboard, there are only 8 ranks and 8 files, but there are 15 diagonals that run up-left and 15 diagonals that run up-right.)
> 2 votes

# Answer
A chessboard is a finite, upright square lattice of size n=8. A rook can move to any position a(1,0) + b(0,1) but a dark bishop can only move to c(1,1) + d(1,-1), where a,b,c,d are any integers that keep the resulting position within the board. Consider for example the position (1,0), which is unreachable by the dark bishop.

This is because the rook's vectors span the upright square lattice, but the bishop's vectors only span half the space.
> 0 votes

# Answer
I think major parts of this is are actually the interactions with other pieces. In particular, one's own pawns and the opponent's king. A rook can create an uncrossable barrier for a king whereas a bishop cannot. And since pawns advance along the file, the rook can protect them their entire journey towards as they advance towards promotion, without the rook having to move.

Additionally, the rook always attacks its maximum number of squares - an entire rank and file. Whereas the bishop's attack power is only maximised when it's in the centre of the board. In any corner, it only attacks one diagonal.
> 0 votes

---
Tags: bishops, pieces, rooks
---


# Question
Title: Is there any software or web service for club-level Elo ratings?
Is there any software (or web-based service) that allows you to keep track of local, club-level Elo ratings?

These ratings would not have any connection with official Elo ratings, it would be just an Elo rating within the universe of players in a club (i.e. games in various social tournaments would compute for the rating).

# Answer
Even if it is not available, something like this is not too hard to implement yourself. Here is an example with extremely silly and simple rating system that is just meant to give you an idea. But I don't think that using actual Elo formula that much harder.

**EDIT:** I edit my implementation to use Elo formula (not including floors) given by the formula here

```
def get_exp_score_a(rating_a, rating_b):
    return 1.0 /(1 + 10**((rating_b - rating_a)/400.0))

def rating_adj(rating, exp_score, score, k=32):
    return rating + k * (score - exp_score)

class ChessPlayer(object):
    def __init__(self, name, rating):
        self.rating = rating
        self.name = name
    def match(self, other, result):

        exp_score_a = get_exp_score_a(self.rating, other.rating)

        if result == self.name:
            self.rating = rating_adj(self.rating, exp_score_a, 1)
            other.rating = rating_adj(other.rating, 1 - exp_score_a, 0)
        elif result == other.name:
            self.rating = rating_adj(self.rating, exp_score_a, 0)
            other.rating = rating_adj(other.rating, 1 - exp_score_a, 1)
        elif result == 'Draw':
            self.rating = rating_adj(self.rating, exp_score_a, 0.5)
            other.rating = rating_adj(other.rating, 1 - exp_score_a, 0.5)

```

This works as follows:

```
>>> bob = ChessPlayer('Bob', 1600)
>>> john = ChessPlayer('John', 1900)
>>> bob.rating
1600
>>> john.rating
1900
>>> bob.match(john, 'Bob')
>>> bob.rating
1627.1686541692377
>>> john.rating
1872.8313458307623
>>> mark = ChessPlayer('Mark', 2100)
>>> mark.match(bob, 'Draw')
>>> mark.rating
2085.974306956907
>>> bob.rating
1641.1943472123305

```

Here is my original python implementation:

```
class ChessPlayer(object):
    def __init__(self, name, rating):
        self.rating = rating
        self.name = name
    def match(self, other, result):
        if result == self.name:
            self.rating += 10
            other.rating -= 10
        elif result == other.name:
            self.rating += 10
            other.rating -= 10
        elif result == 'Draw':
            pass

```

This works as follows:

```
>>> bob = ChessPlayer('Bob', 1600)
>>> john = ChessPlayer('John', 1900)
>>> bob.match(john, 'Bob')
>>> bob.rating
1610
>>> john.rating
1890
>>> mark = ChessPlayer('Mark', 2100)
>>> mark.match(bob, 'Mark')
>>> mark.rating
2110
>>> bob.rating
1600
>>> mark.match(john, 'Draw')
>>> mark.rating
2110
>>> john.rating
1890

```
> 10 votes

# Answer
It seems that rankade, our ranking system for sports, games, and more, fits your needs.

It's free to use and it's designed to manage **rankings** (and **stats**, including matchup stats, and more) for small to large groups of players.

Rankade doesn't use **Elo**, but its algorithm (called *ree* algorithm), although more complex (here's a comparison between most known rating system, including *Elo*, *Glicko* and *TrueSkill*), is similar to Elo if you play 1-on-1 matches only.
> 8 votes

# Answer
I just downloaded and played around with a lightweight freeware item for Windows called ELORater that seems to provide what you're after. You can create a "group" for your club, and then add players to the group, along with whatever initial ratings you want them to have. Then you can just input the results of any games that get played and the program maintains an updated list of player ratings for you.
> 4 votes

# Answer
The free Excel add-in Chess Ranking Assistant found at https://www.add-ins.com/free-products/chess-ranking-assistant.htm uses the glicko system and is menu driven for easy of use. It is designed for chess clubs
> 3 votes

# Answer
If anyone is still looking for something like this, I've build a fairly simple one here: https://github.com/richardadalton/EloRate

At the moment you'll have to host it yourself, but I may offer a hosted service in the future.

-Rd
> 2 votes

# Answer
I recently built https://sortmatch.ca to do this kind of thing. It uses Glicko2 instead of Elo, but the effect is roughly equivalent.
> 1 votes

# Answer
https://skillrank.games

Also allows ratings for team games where individuals change teams between games
> 1 votes

# Answer
http://elorankings.com

Allows you to create custom elo rankings and control certain parameters. Mostly used by video game communities but can be done to create rankings and manage elo ratings for anything. Very easy to use. Keeps complete match history and allows you to individually see a players history, W-L, and how their score changed per match. I use it for a smash tournament I run every week: http://elorankings.com/rankings.aspx?id=1
> 0 votes

# Answer
Yeah sure, you can take a look at http://www.chessfiles.com/chess-software.html
> 0 votes

# Answer
The Irish Chess Union has its rating web application fully released as Open Source and it's available on GitHub: https://github.com/ninkibah/icu\_ratings\_app
> 0 votes

---
Tags: rating, elo
---


# Question
Title: Does the touch move rule apply in Blitz?
At a casual club where I play, one guy insists on playing five minute Blitz games (most of us play untimed games otherwise). Since a player's move isn't complete until they press their clock, he claims that touch move doesn't apply. As such, he sometimes picks up and moves a piece, but then takes the move back when he realizes it would be a mistake, or thinks there is a better move - all before pressing his clock button. Sometimes he ends up moving a different piece than the one he originally touched.

Thus I ask: Is his interpretation of the rule correct, i.e. in Blitz, can a player touch and even move a piece but then take that move back as long as they don't press their clock button? Or is a player still required to move a piece once they have touched it (clearly intending to move it)?

Update: Folks seem to be focusing on the "casual" nature of the games I mentioned. However, I'm more interested in the rules aspect of this question.

# Answer
> 10 votes
**TL;DR:** He is playing "clock-move" which is an alternative to "touch-move." Players should agree to the "move rules" at the start of a casual game.

Alternatively, "*In casual games, the rules are whatever the players agree to*." <sub>(comment by bof)</sub>

---

There is no required "move rule" for blitz, or any other time control. Official USCF and FIDE tournaments I've seen employ the **touch-move** rule as you point out.

In casual, non-rated games one can play any time control (including none) with any "move rule." In **clock-move** games, one can touch a piece but change one's mind about which piece to move as long as one hasn't yet hit the clock.

In my chess club, it is common in unrated games (even with a clock) to allow a player to take back a particularly poor move so one gets a better game (even if you have to point out the opponent's blunder).

The key is having expectations established by the players before the game (or by the event rules).

# Answer
> 3 votes
Since this is about casual games, you don't have to play chess with him if you don't like it. It doesn't matter that you are better or not; **basic courtesy** applies even in games, meaning that both of you should try to make the games enjoyable for both parties. In a comment you said "*this guy stands out and seems to bring up tournament rules, especially when it helps him*", which clearly indicates that he is being discourteous. I would also note that this isn't just about you and him; his behaviour would have negative effect on the whole club (unless he is targeting you, which seem to not be the case).

Another answerer says that players should agree to the rules before starting a casual game. I agree, but I think the above consideration is more fundamental. For most people, courtesy suffices and so neither player needs to even mention "rules". For some people like this guy, it is probably the best to insist on the standard touch-move rule before playing with him. Don't let his behaviour ruin the fun for everyone just because no one feels like being a bit firmer with him.

# Answer
> 2 votes
\[This answer applies to FIDE rules. I don't know about USCF.\]

> Since a player's move isn't complete until they press their clock, he claims that touch move doesn't apply.

By this language, it seems that he's not just stating a rule but actually trying to give an argument based on some ruleset. So you can either ask him what ruleset he is following, and possibly answer to him using the official rules.

In FIDE, touch-move rule applies fully in blitz, and when the clock is pressed does not matter. FIDE laws of chess make a distinction between a move being 'made' and a move being 'complete. In brief:

* A move is *made* if it's legal and the player has released his hand from the piece.
* A move, legal or illegal, is *complete* when the player presses the clock (or the move ends the game, e.g. a mate, stalemate, or another draw rule.)
* After player A has 'made' a move, i.e., released a piece after a legal move (but not necessarily pressed the clock), player B 'has the move' and can start moving a piece, and the touch-move rule starts applying to them.
* There is no special blitz rule about touch-move not applying in some instances, only when the touched pieces have no legal moves.
* Pretty much the only case when the time between releasing the piece and pressing the clock matters is when the move player A made was illegal – then the move has not been 'made' and player A can take the illegal move back and play another move. **But the touch-move rule 4.5 still applies for player A.**

Some relevant parts:

> * 1.3 A player is said to ‘have the move’ when his/her opponent’s move has been ‘made’.
>
> \[...\]
>
> * 4.4 If **a player having the move**:
>     + 4.4.1 touches his/her king and a rook he/she must castle on that side if it is legal to do so
>     + 4.4.2 deliberately touches a rook and then his/her king he/she is not allowed to castle on that side on that move and the situation shall be governed by Article 4.3.1.
>     + 4.4.3 intending to castle, touches the king and then a rook, but castling with this rook is illegal, the player must make another legal move with his/her king (which may include castling with the other rook). If the king has no legal move, the player is free to make any legal move.
>     + 4.4.4 promotes a pawn, the choice of the piece is finalised when the piece has touched the square of promotion.
> * 4.5 If none of the pieces touched in accordance with Article 4.3 or Article 4.4 can be moved or captured, the player may make any legal move.
>
> \[...\]
>
> * 4.7 **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 considered to have been made in the case of**: \[see 4.7.1–4.7.3 for capture, castling, promotion\]
>
> \[...\]
>
> * 6.2 Handling the chessclock:
>     + 6.2.1 During the game each player, **having made his/her move on the chessboard, shall pause his/her own clock** and start his/her opponent’s clock (that is to say, he/she shall press his/her clock). **This ‘completes’ the move.** A move is also completed if:
>         - 6.2.1.1 the move ends the game (see Articles 5.1.1, 5.2.1, 5.2.2, 9.2.1, 9.6.1 and 9.6.2), or
>         - 6.2.1.2 the player has made his/her next move, when his/her previous move was not completed.
>
> \[...\]
>
> * 7.5 Illegal moves:
>     + 7.5.1 **An illegal move is completed once the player has pressed his/her 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.

---
Tags: rules, blitz
---


# Question
Title: What are the strengths of different Chess Engines?
I personally use Komodo most of the time, but lots of people use stockfish. What are the differences between engines and what do they help you improve on better compared to other engines.

Tl;DR Where do Stockfish and Komodo excel in?

# Answer
> 2 votes
People use Stockfish because:

1. It's free.
2. It's the strongest engine. See CCRL for rating list and the fact that Stockfish has been crushing every other engine in the Top Chess Engine Championship.

However: if you're at the level where you don't care about making the best move but rather the move that takes your opponent out of their comfort zone (i.e., you are in the upper echelons of chess skill), then engine strength matters less than the diversity of moves that the engine might suggest. In that case having a wide variety of engines is good, and Stockfish becomes one of many possible tools at your disposal.

---
Tags: engines, learning, stockfish
---


# Question
Title: How to ask an AI engine to test this chess variant?
I would like to use an AI engine to test how well the following chess variant would work: The rules are as in usual chess, except

1. Castling is not possible; instead, the next rule takes its place:
2. When the king is not in check, it can perform the following move: It can switch places with any piece of its own colour on the 8 neighbouring squares around it. Unlike castling, this move can be performed as many times throughout the game as you want. The following special rules apply:
    * It cannot move itself into check by doing so (surprise!).
    * It cannot move pawns to the player’s first rank (where pawns cannot be in ordinary chess either).
    * If it moves pawns to the player’s eighth rank, that pawn will be promoted as usual.
3. Any pawn on the player’s second rank can move one or two pieces forward, even if it has previously moved forward and later been moved back by the king. (This is in order to simplify the game so that you don’t have to remember which of your pawns have moved forward previously.)

The rules themselves do not really matter much. What I would like to know is how an AI engine would play against itself with this ruleset. Based on this, I hope to be able to make my own (human) assessment about how “deep” this variant is. I suppose it is possible to modify the rules given to engines like AlphaZero, MuZero, and Leela Chess Zero and ask the engine to teach itself the game as usual. But are there other, easier methods that do not require extensive rewritings of complicated engines?

I am aware of questions like this one and its answer, but it doesn’t seem that the answer can be adapted to support this variant.

# Answer
Currently there is no “easy” way to do exactly this. The “easiest” way in this case would simply be the right way. You would have to learn a coding language and develop a chess computer using an existing neural network technology.

There are plenty of tutorials online for how to make your own chess computer. You could follow those tutorials, and where it explains how to implement the rules of the game, you would simply implement your own rules in place of the regular chess rules. Once you are finished with creating the game, you would probably want to use NEAT to train an ai to play it. NEAT stands for Neuro Evolution of Augmenting Topologies.

Before putting this massive amount of effort in, I suggest reading the following study: Assessing Game Balance with AlphaZero: Exploring Alternative Rule Sets in Chess.

In this study, they forced the DeepMind project to play variants of chess that didn’t really exist. The most interesting variation was one where pawns could move, but not capture, sideways, in addition to their other moves.

They found that changing the castling rules did not produce much interesting gameplay, though I will note that none of their rules gave the king infinite quasi castling power like you’re describing.

Perhaps the easiest way to do this would be to use our imagination. I am a variants enthusiast and atomic player so I will give it my best shot.

The King is the most important piece in the game and defending it is the most important goal, second only to capturing the opponent’s King. This tells me that the most likely application of your rule change would be to defend the king one move before potential checkmate. There would also be special endgame circumstances where once the majority of pieces were off the board, the king would then carry a pawn on its back to promotion. For example, the king could prevent a pawn from ever being on a dark square against a dark square bishop.

In addition, moves that improve king position and the position of another piece could become strategy. The concept of moving two pieces at once could be seen as overpowered and preferred to the usual methods.

Finally, the last effect from your rule change could be an increase in king walks. There are a handful of grandmaster games where one side for whatever reason has to get up and run, and after 10 or so king moves finally there is room to breathe to deliver a deadly attack. More movement options for the king would make these oddly long king walks more possible to accomplish.

In terms of depth, it would be technically deeper than chess since it offers more move possibility. Which giant number to compare to shannons number I wouldn’t know how to calculate.

If that doesn’t sound interesting to you, how about a variant where any piece can do a neighborly swap? Now that would create a game that looks alien to players.

All in all the answer to this question is yours to decide, but hopefully this gives you some insight as to what goes into this sort of thing.

Edit: OP pointed out that this rule change now allows bishops to swap colors. This opens up possibilities for bishops to defend eachother. As early as move 1 you could elect to have two same color bishops.
> 3 votes

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


title: Scid Vs. PC | Using Stockfish on Linux

text:
# Question
Title: Scid Vs. PC | Using Stockfish on Linux
I have downloaded Stockfish 16 from their site at:

https://stockfishchess.org/

Using the command line in linux (I'm a newb), I have compiled it in the 'src' folder. After this, the exec file appears and Stockfish appears to run fine in the command line.

But when I go into Scid Vs. PC and try to add Stockfish as an Engine, it does not detect it.I get a notification that reads:

**The analysis engine terminated without exit code: ""**

I have tried several different command & directory pathing combinations, including using the program to browse directly to the exec itself to avoid error. No success.

Anyone have any suggestions? I've been through several sites and keep seeing variations of my issue but no resolution.

# Answer
> 0 votes
I had the same issue. I have a Linux machine, but like you, I do not know too much about Linux. Everything depends on the version of Linux that you are using. What I did was to search on YouTube. I found a video that guided me step by step. The following link is a search for STOCKFISH LINUX INSTALL SCID: https://www.youtube.com/results?search\_query=stockfish+linux+install+scid

It would be better if you use STOCKFISH UBUNTU INSTALL SCID, if you are using Ubuntu.

Something interesting is that newer versions of Stockfish or Linux do not change too much the process of installation.

So, YouTube is your Salvation Army!

Good luck!

P.S. I noticed that you are using SCID vs PC. Most likely, the same will work for that option. If you do not find one for that purpose, use SCID instead of SCID vs PC for the search of information. They are connected programs.

P.S.#2 Additionally, you can go to the following question, and ask to the people who answered it: Why can't I put Stockfish in SCID?

---
Tags: engines, software, stockfish, scid
---


# Question
Title: Chess-like games and exercises that are useful for chess coaching
Chess 960 popularised by Fischer could be useful to teach opening principles (mainly because the players has to think about development consciously). LaPingvino asked "What other games or chess variants are useful to improve your chess skills?" (by the way, its current answers include blindfold chess and Japanese chess).

I am interested in exercises and games that are useful to teach chess. This is beyond the scope of LaPingvino's question since exercises are included. There are exercises and games already used to teach chess especially to complete beginers, such as maze and capture the stars (e.g. lichess). Feel free to include exercises and games you create (provided they are useful in chess coaching).

**Please post only one exercise or game per answer**, and mention its utility in a chess coaching program as bullet points. You are welcome to write cons as well. Many chess variants are discouraged to use in chess class because of game dynamics being very much different from chess.

Also, **I request to vote the answers based on the *utility* in a chess coaching program**, not by the appeal of the exercise/game of itself.

PS: To chess coaches interested in including chess-like games, I would recommend to select a small number of chess-like games, and to ensure that they are visually different from each other and from chess.

# Answer
> 4 votes
Game: **Race to the Finish**

I play this with the juniors at my local club to help them build their pattern recognition and endgame skills, not sure how it would work online

## Audience

All levels

## Pros

* Encourages calculation
* Builds habits and pattern recognition

## Rules

Normal rules of chess apply. A starting position is chosen that leaves the white player completely winning with a zero or almost zero chance of losing or drawing

The position is set up on multiple boards (2 is normal, but no reason you can't do more)

One player who is confident they can play optimal or close to optimal moves (such as the tutor) will play the black pieces on all boards and plays with the goal of surviving the lost position as long as possible

Each of the competitors (students) plays on one board as white. They each play one move, then the tutor plays one move on all boards, to ensure the move count on all boards stays in sync

The goal for the competitors is to checkmate in as few moves as possible, they are racing against each other. Whoever gets checkmate in the fewest moves is declared the winner, and the other board(s) can then be abandoned or played to a finish just for fun

The starting position is decided by the tutor and can be tailored to the ability of the competitors, for example for complete beginners you might have a simple K v KRR or K v KQ, and for intermediate players you can select more complex positions such as KP v KRP where the competitor needs to calculate if its worth 'spending' the moves to promote their pawn or just go ahead and mate with the lone rook. Advanced players can get the same entertainment by applying increasingly complex starting positions

# Answer
> 3 votes
Exercise: **Maze**

## Audience

Complete beginners

## Pros

* Much simpler compared to chess

## Rules

The player has only a few pieces (sometimes only 1 piece), and oppenents pieces are frozen (they do not move). A square is marked as target. The aim of the exercise is to get a piece to the target square by moving pieces using their standard chess movement.

A more complicated variant include forbidding moving pieces to squares where they can be captured by enemy forces.

# Answer
> 1 votes
Game: **Chess 960** (also called Fischer random chess)

## Pros

* Forces players to think conscisouly about development rather than playing a memorised line.

## Cons

* The castling rules are too complicated compared to chess

## Rules

Before the game, a starting position is randomly determined and set up, subject to certain requirements. White's pieces (not pawns) are placed randomly on the first rank, following two rules:

1. The bishops must be placed on opposite-color squares.
2. The king must be placed on a square between the rooks.

Black's pieces are placed equal-and-opposite to White's pieces. (For example, if the white king is randomly determined to start on f1, then the black king is placed on f8.) Pawns are placed on the players' second ranks as in classical chess.

After setup, the game is played the same as classical chess in all respects, with the exception of castling from the different possible starting positions for king and rooks.

## Links

General info.: Wikipedia
(Forum) discussions: chess.com, lichess.org, chessbase.com

# Answer
> 1 votes
Game: **Race** (new)
This is a gamified version of maze.

## Audience

Complete beginners

## Pros

* Consistent with the chess rules (except the rules for ending the game).
For example, players turns are correct.

## Rules

In race, there is no king & pieces are almost randomly placed on board. A target square is marked for white, and one for black. Whoever reaches their target square first wins.

Comment: I usually this before students know about capture.

# Answer
> 1 votes
Exercise: **Capture the stars**

## Audience

Complete beginners

## Pros

* Much simpler compared to chess

## Rules

The player has only a few pieces (sometimes only 1 piece), and there are no opponent pieces. A number of squares are marked by stars. The aim of the exercise is to capture all stars.

To make the exercise a bit more challenging, encourage students to complete the task with as few moves as possible.

## Links

Available to play on: lichess, chessMatec for kids (both available as mobile apps)

# Answer
> 1 votes
Game: **Capture all**

## Audience

Complete beginner to Intermediate

## Pros

* Allows student to figure out the importance of the material/force aspect of chess by themselves (e.g. gives practice on hanging pieces and exchanges).

## Cons

* Games could get too long (and probably complicated).

## Rules

The initial position is the same as in chess, except for absence of kings. The aim of the game is to capture all opponent pieces.

A variant of the game include both kings in the initial positon, but there is no check or checkmate.

*Comment:* One could use a different set of pieces at the start of the game and/or use a different starting position. Starting with only a few pieces which are suitably placed could make the game shorter.

## Links

General info.: Greenchess

# Answer
> 1 votes
Game: *Knights dominate the board*
(goes by different names)

## Audience

Complete beginners
(The purpose is to teach movement of knights)

## Cons

* The rule that visited squares cannot be revisited is an important part of this game, which is not in chess.

## Rules

In this variant, both sides have only knights and they have the same number of knights (typically 1 or 2). The board size could be different from 8x8, and there is a lot of choice of intial positions. Capturing is not allowed. Player move in alternate turns. A square visited earlier cannot by re-visited (in one variant, squares visited by oppenent knights cannot be re-visited, but no problem with squares visited by player's own knights). Let's call these no-revisit rule and no-opponent-revisit rule.

The aim of the game varies between variants. With no-revisit rule, the game ends when a side has no more moves. With no-opponent-revisit-rule, the game ends when the number of squares visited by a side reach a stipulated number (e.g. visit 13 squares to win the game).

In some variants, a piece is not allowed to move to square under the attack of an opponent piece.

## Links

In mobile app omnichess: benighted

# Answer
> 0 votes
Game: *Inspired by Horde Chess*

I think it sould be possible to make a chess position with only pawns and king for white and usual chess pieces for black (not necessarily whole army). But, I am not sure which of those positions are more useful to chess students.

(Feel free to edit the post if you can list particulary useful horde-like chess positions)

## Pros of Horde Chess

* Player plaing as white could learn piece coordination, and the one playing as black could learn pawn storming (also, endgame tactics and tactics involving passed pawns).

## Cons of Horde Chess

* The game dynamic is very much different from chess
* Looks very much like chess (but, exactly one player has king, which is comforting).

## Rules of Horde Chess

Horde Chess is a chess variant where Black starts with the regular chess army and White with nothing but 36 pawns. The playrs take turns, and white starts first. White's goal is to checkmate the black king. And black's goal is to capture all of White's pawns (and promoted pieces).

There are several variants of Horde chess (e.g. see Dunsany's chess)

# Answer
> 0 votes
Game: **Set up chess**

## Cons

* The piece placement phase (which is not a part of chess) has *a more prominant role* than the rest of the game (which is like chess).
* Piece placement at the start of the game is very specific to the variant rather than being close to piece activity and corrdination in chess

## Rules

Before the game players set up their pieces and pawns, one by one. Each player has 39 material points to spend. Pieces can be placed on the first 3 ranks, pawns on the 2nd and 3rd ranks.

## Links

Available to play on: chess.com

# Answer
> 0 votes
Exercise: **Coin collector**
(similar to Capture the stars)

## Audience

Complete beginners

## Pros compared to "Capture the stars"

* Slightly simpler if the player has pawns (otherwise, the two games are the same).

## Rules

Coin collector is almost the same as "Capture the stars" with coins instead of stars.
The only difference is that a **coin** on a square could be **collected** not only **by capturing** the coin but **also by moving to that square**.

(included as separate exercise for quick reference)

# Answer
> 0 votes
Game: **Coin collector: Versus mode** (new)
(Gamified version of coin collector, adapted a bit)

## Audience

Complete beginners

## Pros

* May be useful to teach occupying and controlling centre
(e.g. start with chess starting position and place 16 coins on the exetended centre).

## Rules

This is almost a generalisation of the race game.

Initial position could be the starting position of chess (or not) with an odd number of coins on empty squares (only one coin per square). Either both kings are present in the intial position or both are absent. The players take turns. An empty square occupied by a coin does not block movement of any piece through that square. If both kings are present in the initial position, winning is by either checkmating the opponent or by collecting more than half of the coins (e.g. 4 coins if there are 7 coins in total). If both kings are absent, the only way to win is by collecting more than half of the coins.

## Links

Similar game: benighted in omnichess app

Comment: "benighted" is almost a special case of this game (with a 5x5 board, 2 knights per player, and one coin on each square including the squares of the knights at start).

# Answer
> 0 votes
Game: **Vote chess**, adapted for chess class

## Audience

Intermediate

## Pros

* A good practice for move selection and decision making (variant 1 is especially a good training to look for candidate moves, and then consider them one by one).

## Rules

The only difference from normal chess is that two teams play the sides. Team 1 plays white against team 2 on a single board. The move to be played by a team is decided by voting of members. When used for a chess class, two variants are useful. In variant 1, first, a player from team 1 proposes two candidate moves. The rest of team votes between the two moves (discussion not allowed), and the move with most votes is played as the team's move. Then, it's black turn and the same process is done with Team 2. Next, it is white's turn again, and this time another player gets to propose two candidate moves. The game continues in this fashion. In variant 2, the only difference is that 2 or 3 members of the team propose one candidate move each instead of one member alone proposing candidate moves (the next time the team should make a move, another 3 members propose candidate moves).

The advantage of variant 2 over variant 1 is that there will be less blunders in the game.

Initial position of the game need not be the starting position of chess.

# Answer
> 0 votes
Game: *Chess from (selected) custom position*

This is a popular exercise, and even thematic tournaments have been conducted (e.g. rice gambit tournament).

## Audience

Past-beginners and higher

## Pros

* Good for opening training in an enjoyable way

## Rules

Same as chess, but from a custom position. If the purpose is opening preparation, it is better to start with a well trodden opening line (say, after 8 to 10 moves) and ask to continue the game from there. Good candidates for such starting positions include the few selected positions that Seirawan recommends students to play out in "Winning chess openings".

This exercise could be used as the game part of a chess session (its merit over standard chess is shorter games). In this case, it is better to choose an initial position where both sides need to make some moves to develop pieces (so that piece development is also tested).

**Note:** Answered on behalf of Seshadri K. R.

---
Tags: chess-variants, teaching, coach
---