Comments/Ratings for a Single Item
The following terms struck me as uncommon, and on checking, I have not found them used:
- air squares
- capture leap
- CVPhile
- distant square
- finite mover
- heraldic piece
- infinite mover
- leap passively
- leap square
- line move
These have been used very little:
- capture zone is used in Outer Space Chess, where it is defined as " the set of squares on which a piece could potentially capture another, were it to be there."
- counter. While the word appears on numerous pages, I did not find any using it to mean a physical object used as a Chess piece, and it was sometimes used to mean another object used in conjunction with a Chess piece to alter its attributes or identity.
- custodial capture is used in Minima and Latrunculi XXI.
- cycle. While used in English Progressive Chess, as mentioned in the entry, I did not find any other game using it in the same sense.
- leap to capture is used once in Leap Chess, though apparently with a less strict meaning.
- line piece is used in Omega Chess and Grander Chess.
- marker is more commonly used to mean some object on the board besides a Chess piece. Same problem as counter.
These are terms I personally consider unconventional and do not use:
- array (I favor setup or initial setup)
- cell (I favor space)
I'm going to take a break now and continue this later.
H. G. Muller wrote on Fri, May 1, 2020 05:42 PM UTC:I would like to propose a definition of 'pass through check' as "passing through or jumping over a square where it would have been illegal to move your royal to, had that square been empty".
I see the current glossary doesn't contain a definition for 'check'. One could define it as a situation where a royal could be pseudo-legally captured if the player currently on move would pass his turn. But there could be a variant 'Recursive Chess' where it is not allowed to capture a royal when it exposes your own King. So it is perhaps better to define a legal move as a pseudo-legal move that does not expose your royal piece to capture, with the note that a move that terminates the game would never expose anything. Some game-termination rules are such that the actual game result is determined by an 'after-move': E.g. in Shatranj you can win by baring the King, unless the opponent can bare your King in the next turn (in which case it is draw). Or, presumably, when he could capture your King (in which case you would lose by having played an illegal move). So on King baring, he gets an after-move. Variants like King of the Hill allow you to make the winning move to the center only if that move was legal, i.e. reaching the square is not enough, but there is an after-move that reverses the result when it can capture your King. And in Tai Shogi the royal is an Emperor, which can capture to any square on the board. Except that he cannot expose himself to recapture when capturing a royal. So there is an after-move in Tai Shogi even after capture of the royal, and the capture of the Emperor in this after-move has priority in deciding the game result over capture of the first royal! Recursive Chess could also be formulated that way.
So you are in check if the opponent, would it be his turn, has a winning pseudo-legal capture on your royal piece. In orthodox Chess any capture of the King would be instantly winning. But in Recursive Chess capturing the King with a pinned piece, (or in Tai Shogi capturing a protected Emperor with your Emperor) would be a losing capture, as in the after-turn your own King would be taken. So you would not be in check when you expose your King to capture by a pinned piece (or when your Emperor is protected). In al cases this can then be combined with the rule that moves that put your own royal in check are illegal.
Greg Strong wrote on Fri, May 1, 2020 06:14 PM UTC:I think 'bare King' is fine to keep here, but I would remove the entry for 'bare King rule'. I think a list of terms should not include rules. Granted, there is a fine line. For example, I think en passant and castling should be here - but they should be described here in a general way.
The definition of castling presented here dictates rules for exactly how many squares the king should move and that is far too specific in my opinion. I would say something more like 'A move that was added to chess to speed up the game wherein the king and the rook both move in order to simultaneously move the king to safety and develop the rook. This is typically subject to several restrictions.' Then I think it would also be good to link to a page on castling (yet to be written) where more information can be given about the history of the move, the specifics in chess, how it has been adapted to other variants on larger boards, etc. We have a page called 'Castling in Chess 960' which seems too specific to have its own page. (And we typically refer to this game as Fischer Random in other places.) If this is agreed, I will start working on writing a Castling page.
A castling page is a good idea. Things to cover include castling in Chess, longer castling, as in Capablanca's Chess, free castling or enhanced castling, as it is called in Aberg's Capablanca variation, flexible castling, which I introduced in Grotesque Chess, Fischer Random Chess rules for castling, and this new type of castling that Aurelian Florea is calling fast castling.
H. G. Muller wrote on Fri, May 1, 2020 09:46 PM UTC:Although the term 'pseudo-legal move' is standard jargon amongst chess programmers, I am not sure if it would ring a bell with the typical chess player. If this isn't the case, I am not sure if we should keep this term, or perhaps introduce another term for this that sounds less technical. How about 'valid'? A move would be 'valid' if it complied with the rules for moving that particular piece type, irrespective of whether it would comply with any restrictions on exposing (royal?) pieces to capture. A move would be 'legal' if it complies with all rules of the game.
H. G. Muller wrote on Sat, May 2, 2020 09:34 AM UTC:I propose to change the definition of 'attack' by the following:
- A piece is under attack when the opponent, would it be his turn, could *legally* capture it in the current position.
- A square is under attack from a player when that player could *legally* capture an enemy piece standing on that square, given the remaining board occupation.
- Colloquially, 'to attack' can also mean "play a move that creates one of the above situations".
Where *legally* would refer to the term 'legal', defined as:
Moves are legal when they would comply with all rules of the game. Moves are called pseudo-legal when they they comply with all rules except those that forbid to leave certain pieces (usually called *royals*) exposed to capture after a move.
Where *royals* would refer to an entry for 'royal':
A piece type is called 'royal' when capture or elimination of it terminates the game. With only a single royal per player, capture implies elimination. In some CVs a player can have multiple royals. We can then distinguish absolute royalty (first capture of a royal terminates the game) from extinction royalty (elimination of all royals of one player forces game termination).
CVs often have the rule that it is not *legal* to expose yourself to a game-terminating move of the kind described above that would result in your loss. (See *check*, *mate*.) In this case the mentioned captures cannot be part of any real game, and are only used as hypothetical continuations after moves that are not legal, to establish their illegality.
And for 'check':
A player on move is said to be 'in check' when his opponent, if he were on move, would be able to instantly decide the game in his advantage by capturing a *royal* piece.
(The condition that the capture should be a win is added to exclude cases like Tai Shogi, where capture of a royal by an Emperor would be a loss if recapture is possible. The word instantly was added to exclude situations where the capture of one of multiple royals is merely the first move of a forced winning line. Perhaps the term 'instantly decide' should be replaced by 'terminate', which could then get its own definition in the glossary.)
For 'mate':
A position where the player on move has no *legal* move is called a 'mate'. We distinguish checkmate (when mentioned player is also in *check*) and stalemate (otherwise), and the rules of the CV often assign a different result to those.
Possible entry for 'terminate':
A move is said to terminate a game if it fixes the game result without the players having to play any more moves. This does not exclude that the move is followed by a number of automatic hypothetical moves ('*after-moves*') to determine that the termination condition is indeed fulfilled, and what the game result should be. (E.g. *checkmating* terminates an orthodox Chess game, but two more hypothetical half-moves would have to follow to establish whether the royal can indeed not escape capture.)
After-move:
An after-move is a move in a hypothetical continuation of a *terminated* game for the purpose of determining whether the termination condition was fulfilled, was reached through a move that was *legal*, or what the game result is. E.g. when *baring* the opponent King is a winning game-terminating condition, an after-move can be needed to establish whether the capture that achieved it did not put your own King in *check*. If the result should be adjusted to draw when the bared opponent can counter-bare you through a legal move, two after-moves are needed. In this respect baring differs from capture of a *royal*, which typically does not allow an after-move, and thus never exposes your own royal to anything, so that any pseudo-legal move is also legal. The number of after-moves that should be taken into consideration, and their effect on the game result, is an essential part of definition of the winning condition.
I will get to the suggested revisions in due time, but for now, I want to continue with the first stage, which is to identify terms that may be removed. I left off in the Ms.
These are rarely used:
- move obliquely is used only in Oblique. It may be enough to define the word oblique.
- move passively is used in only a few variants: Lemniscate Chess, Chess with Ultima, Rococo and Supremo Pieces, and Battle of the Six Armies. It could be replaced with "moves without capturing," which would be clearer in meaning and not require its own glossary entry.
- move radially is used only in Tenjiku Shogi, where it has no link to the glossary. It may be enough to include a definition for radial.
- The phrase "move to capture" is common, but apparently not with the definition given for it, which doesn't even make any sense to me.
- neighboring squares is rarely used. This could be shortened to just neighboring. I want to reduce the use of terms with squares, because spaces can be other shapes.
- oblique move
- oblique square
- The word "option" is frequently used but probably not always in the narrow sense of "move option."
- overtake is used only in Checkers with Bosses.
These are not used:
- move zone
- non-capture square
I will stop here for now and continue next time with the Ps.
Continuing with P:
These are not used:
- passive leap
- passive piece (its few uses are not with the glossary definition)
- passive square is used by Charles Gilman in Stock Goes East 49 files, Man and Beast 21, and Fiancé Chess.
- range capture. The more common term is rifle capture.
- rearward diagonals
These are rarely used:
- passive move is used in Tiger Lily Chess and Xiangqi.
- pocket piece appears only in two articles on fairy chess problems.
- points is normally used with other definitions. It is used once on Xiangqi, which just points out that intersections are called points. That could be removed. Point is an uncommon word for intersection.
- radial move appears mainly in some piece articles and a couple games by Charles Gilman and in my Alibaba article.
- radial square appears in Gilman's Mixed Radial Hex Chess, but only to describe another of his games.
- range piece appears mainly in phrases like short-range piece, long-range piece, and mid-range piece, which have nothing to do with the definition given. The definition is for pieces that capture from a distance, such as those in Rifle Chess, but that game's page does not use the term.
- reserved piece is used only in Summoner's Chess.
These seem redundant or unnecessary
- promotable. It's enough to have promote.
- properties is a common English word, and the definition just says see move options.
It's time to take a break again. I'm in the Rs.
Continuing in R:
These are not used:
- rotating piece
- X-Y leaper
These are common words that don't seem to be used much in the sense given:
- screen is often used in other senses, such as a divider for lettings players set up their pieces without the other player seeing. In the sense given in the glossary, it is used on some pages, such as Gross Chess. I'm not sure that the term is heavily used. The term is used by Pritchard in his Xiangqi article.
- see is mainly used in the usual sense. I did not see it used in the glossary sense of a piece seeing.
- species is typically used in other senses, and it could be replaced with "type of piece" or "pieces of the same type" depending on how it's used.
- standard square is normally used in the longer expression "standard square board," not in the glossary sense. The definition of standard move would be less confusing without using this term.
- standard piece seems to be used in the sense of a commonly used or usual piece, not in the glossary sense of a piece capable of only standard moves.
- starting piece is not used very much and is fairly self-explanatory.
- straight-rearward is used only in Maorider Chess, and it is fairly self-explanatory.
- target square is sometimes used in the sense of a space that must be reached to win the game. When it's used in the glossary sense, the context may make its meaning clear enough.
- The only use of "two move rule" in a game is in reference to a different rule.
These seem self-explanatory enough to not need a glossary entry:
- straight-forward
Now I'm done. I didn't list piece names, game names, and other things we have links to, but these could also be removed.
I am now compiling data on which pages have links to the glossary, and which terms have actually appeared in glossary links. Here is a link to glossaryentries.txt, which I created by piping some grep searches into the same file. This only contains data on .html pages. It doesn't tell anything about submissions in the database. I hope to process this data later to get a list of terms that links have been made to the glossary for, but it's time for me to switch gears.
I have now processed the raw data into a list of keywords. I have not removed duplicates, but they indicate how popular a term is.
3dboard 3ddiagonals array array array array array array array array array array array array array array array array attack attack attack attack bare_king bare_king bare_king board_move capture_move capture_move capture_move capture_move capture_move capture_move capture_move capture_move capture_move castling castling castling cell cell cell cell cells cells cells colorbound colorbound column control control control control control control control control control coordinalplane coordinal_plane coordinate_plane custodial_capture custodial_capture cycle defend defend departure_square diagonal_direction diagonal_direction diagonal_direction drop drop drop drop drop drop enemy_piece en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture en_passant_capture file friendly_piece friendly_piece hex hex home_square home_square hop hop hop hop hop intervening_piece intervening_piece intervening_piece intervening_piece in_hand leap leap line_piece move_options move_passively move_passively move_passively move_passively move_passively move_passively move_passively move_passively orthochess orthochess orthochess orthochess orthochess orthodox orthodox orthodox orthodox orthodox orthodox orthodox orthodox orthodox orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthodox_chess orthogonal_direction orthogonal_direction orthogonal_direction orthogonal_direction orthogonal_direction orthogonal_direction orthogonal_direction orthogonal_direction overtaking overtaking overtaking overtaking overtaking palace palace palace palace palace palace palace palace passive_move passive_move passive_move passive_move passive_move passive_move passive_move passive_move passive_move point point point point point point point point point point point point point point point point point point point promoted_piece promoted_piece promotion_zone promotion_zone promotion_zone promotion_zone rank rank rank rank rank reserve_piece reserve_piece river river river river river river river river river river royal royal_piece royal_piece screen screen screen sequence sequence sequence square square stalemate starting_piece starting_piece starting_piece starting_square starting_square starting_square
Greg Strong wrote on Sat, May 2, 2020 10:49 PM UTC:Here is the same list with the terms grouped and counted, in descending order:
34 en_passant_capture
19 point
16 array
16 orthodox_chess
10 river
9 control
9 orthodox
9 capture_move
9 passive_move
8 palace
8 move_passively
8 orthogonal_direction
6 drop
5 rank
5 hop
5 orthochess
5 overtaking
4 attack
4 promotion_zone
4 intervening_piece
4 cell
3 diagonal_direction
3 starting_square
3 starting_piece
3 cells
3 sequence
3 screen
3 bare_king
3 castling
2 custodial_capture
2 defend
2 colorbound
2 leap
2 friendly_piece
2 square
2 home_square
2 royal_piece
2 reserve_piece
2 promoted_piece
2 hex
1 3ddiagonals
1 stalemate
1 board_move
1 royal
1 move_options
1 column
1 enemy_piece
1 coordinal_plane
1 coordinalplane
1 coordinate_plane
1 in_hand
1 cycle
1 departure_square
1 3dboard
1 file
1 line_piece
Thanks. I did the database by manual inspection, because there weren't a lot of submissions with links to the glossary. The only new terms were promote and threatened, the latter being one I added just recently.
Most of these terms can stay. We might not need to keep overtaking, cycle, sequence, line piece, or move options. Of coordinal_plane, coordinalplane, and coordinate_plane, only the first one is correct.
I propose to change the definition of 'attack' by the following:
- A piece is under attack when the opponent, would it be his turn, could *legally* capture it in the current position.
- A square is under attack from a player when that player could *legally* capture an enemy piece standing on that square, given the remaining board occupation.
- Colloquially, 'to attack' can also mean "play a move that creates one of the above situations".
Let me first clean up the English on this:
- A piece is under attack if the opponent could, were it his turn, *legally* capture it in the current position.
- A square is under attack from a player when that player could *legally* capture an enemy piece standing on that square, given the remaining board position.
- Colloquially, 'to attack' can also mean "play a move that creates one of the above situations".
I disagree with the first two definitions. I'll start with the first. In Fusion Chess, for example, whether a compound piece is attacked affects whether it can split apart. This is unaffected by whether the attacking piece is unable to make the capture due to being pinned. Furthermore, this definition introduces a recursive factor into the evaluation of whether one piece is attacking another. To know whether one piece is attacking another, you would have to know how the powers of other pieces affect the movement of that piece.
I would propose the following instead:
1. One piece is attacking another when it has a capturing move that can reach its space, and it is normally allowed to capture or check that piece*. In situations where the only consequence to come from being attacked is being captured, an attack may be considered real only if a capture can actually be made. But in situations where attacking a piece can affect its powers of movement or the outcome of the game, it is normally assumed that other conditions in the game that could prevent the capture, such as being pinned, do not affect whether one piece is attacking another. For example, being pinned would not stop a piece from attacking the enemy king.
2. A space is under attack for a particular piece when moving there without any other changes to the position would expose it to attack in the first sense.**
3. Colloquially, "to attack" can also mean to play a move that creates one of the above situations.
* In most Chess variants, pieces are not allowed to capture pieces belonging to the same side, though exceptions may be made in individual variants. In Korean Chess, cannons are not allowed to capture each other even if they belong to different sides.
** In Chess, any space that is under attack for one piece will be under attack for all pieces belonging to the same side. But in other games, a space could be under attack for one piece but not for another. For example, if a black cannon were on a1, a white king on e1, a white rook on h1, and nothing else on the rank and nothing else attacking it, the spaces f1 and g1 would be under attack for the rook but not for the king. The restriction against castling through check would not stop the King from castling, though the restriction on moving into check would.
H. G. Muller wrote on Sun, May 3, 2020 03:22 PM UTC:I think the problem here is that there are actually two different forms of 'attacked'. Perhaps it is better to make that explicit by giving them different names, rather than call them the same, and specify under which conditions one definition applies, and under which another. It is hard to foresee whether there will occur cases which would like to use one definition, which we inadvertantly assigned to another. For instance, your criterion of outcome determining doesn't seemt to apply to Tai Shogi: capturing a royal can end the game, but it is not legal for an Emperor (which is a universal leaper, and thus always has every piece in its reach) to do it when the royal was protected. So normally a protected royal is not considered attacked by the opponent's Emperor. So this is a case where legality of the actual capture does matter.
In chess-programmers jargon on uses the qualification 'pseudo-legal' to indicate that rules for checking should not be taken into account. Making the way pieces move dependent on the checking rules indeed introduces recursion in the definition. But it cannot be excluded that this is exactly what the designer of a variant intends. I already mentioned 'Recursive Chess', which is FIDE except that it is not legal to expose your King to capture even for capturing the opponent's King. The recursion is innocent, because it always terminates: there are only two Kings that can be captured. The difference with FIDE can be formulated in terms of an after-move: in FIDE there is no after-move after King capture, so the player whose King is captured can never retaliate; he has already lost. In recursive Chess King capture grants one after-move, and if that also captures a King, the player that made the second capture wins! (Making the first King capture illegal, as it is forbidden to expose yourself to an immediate loss. So you would not be in check by pinned pieces in Recursive Chess.) This is similar to King baring in Shatranj, where the bared player gets an after-move to counter-bare, and salvage a draw that way.
So I think it is better to explicitly distinguish (legal) attack from 'pseudo-legal attack'. The FIDE checking rule could be formulated as "it is not allowed to expose your King to pseudo-legal attack". (IMO any pseudo-legal attack on a King would also be a legal attack, because in FIDE you get no after-move to retaliate after King capture. But not everyone might agree with that interpretation, or even be aware of it, so it is always better to explicitly add the 'pseudo-legal' qualifier.) Similar, in the move rules of Fusion Chess it would be proper to stress that it are pseudo-legal attacks that have consequences for splitting.
To keep the definition of 'attack' simple, we could just take out the word *legal* from the definition I proposed, and add the sentence:
We can distinguish *legal* attacks from *pseudo-legal* attacks, depending on the nature of the involved capture.
where both links would point to the entry for 'legal' in the glossary, with the definition I proposed.
You have a good point about the piece-type-dependent nature of squares being attacked. Chu Shogi forbids Lions to capture each other from a distance, but only when they are protected (i.e. recapture is possible). I have always seen this as a rule similar to the FIDE checking rule, where you cannot expose a Lion to recapture, rather than a King. (Chu Shogi has no checking rule for its King.) So Ln x protected Ln would still be pseudo-legal. There has indeed been discussion whether that rule should be interpreted recursively or not, in cases where more than two Lions are involved. For the Janggi Cannon CxC is always forbidden, though, so it cannot be explained as it not being legal to expose your Cannon. The Ultima Chameleon is another piece that captures different victims with different moves.
The problem with 'attacked' for a square is that it is not obvious what you should imagine to be on it. Most likely the issue of an attacked square comes up in connection with describinbg the move of some piece, and that would make it natural to assume a piece of that type on it. That can still be different from imagining an actual piece moves there, as the disappearence of that piece from its old location could affect whether captures to the square are possible. E.g. a lame Dababba on d1 would not attack f1 when the King is still on e1. Can white castle O-O? I would say not; if the King moves to g1 in two steps, after the first step the Dababba can capture him. So he would be moving through check. If there had been a Cannon on d1, it would have attacked f1 before the castling, but no longer after the first King step. (But of course you would end up in check once you would put the Rook on the other side of the King.)
I think I'll rewrite the first part of my proposed definition of attack a bit:
1. One piece is attacking another when it has a capturing move that can reach its space, and it is normally allowed to capture or check that piece*. In situations where this condition has any bearing on the rules, it is commonly understood that this is unaffected by whether other conditions in the game, such as the piece being pinned, would prevent the capture. An attack where capture is made impossible by other conditions may be called an impotent attack, and where it has no effect on the rules, its significance may be judged by the player facing it.
I don't like the term pseudo-legal, because it suggests something that is legal-like without actually being legal. For example, pseudoscience is understood to be fake science, not something that could sometimes be real science but doesn't have to be.
For instance, your criterion of outcome determining doesn't seemt to apply to Tai Shogi: capturing a royal can end the game, but it is not legal for an Emperor (which is a universal leaper, and thus always has every piece in its reach) to do it when the royal was protected. So normally a protected royal is not considered attacked by the opponent's Emperor.
This is covered by the condition that it has to have a capturing move to the space. An emperor does not have a capturing move to a space occupied by a protected royal piece.
The problem with 'attacked' for a square is that it is not obvious what you should imagine to be on it.
I actually made it very explicit what would be on it. A space is not under attack in general. It is under attack for a particular piece that could move to or pass over that space.
H. G. Muller wrote on Sun, May 3, 2020 06:53 PM UTC:I don't like the term pseudo-legal, because it suggests something that is legal-like without actually being legal. For example, pseudoscience is understood to be fake science, not something that could sometimes be real science but doesn't have to be.
I agree, but it happens to be the standard term. It is a very useful concept, so I think that when we don't like the name, we should just find another name for it. I already coined the term 'valid move'. I suppose 'semi-legal' suffers from the same problem as 'pseudo-legal'. 'Proper move' would be another possibility. A problem is that for these terms it is not obvious that they might conflict with legality. How about 'near-legal' or 'close-to-legal'?
This is covered by the condition that it has to have a capturing move to the space. An emperor does not have a capturing move to a space occupied by a protected royal piece.
I don't think so. The Emperor does have a pseudo-legal move to that square. That it cannot use it is just because it would expose itself (the royal) to capture, just as moving a pinned piece would. So if you mention pins as an example of things that should not be taken into account for game-terminating moves, it is not obvious at all (and would even be very illogical) that stepping into check with the royal itself would not be excluded too. Note that in the FIDE case K x K is allowed, even when the captured King is protected: I cannot step my King next to the enemy King even when my King is protected there. You would be able to do that in Recursive Chess, btw.
Greg Strong wrote on Sun, May 3, 2020 07:20 PM UTC:I think we should stick with pseudo-legal. It is established terminology and it is close enough IMO.
That said, quasi-legal is a possible alternative.
I was going to look up Tai Shogi, but it appears we do not have our own page for it. Maybe I'll look up another page on it tomorrow, but it's late right now.
H. G. Muller wrote on Mon, May 4, 2020 08:09 AM UTC:Yeah, the shear size of Tai Shogi so far deterred me from making a page for it. You could look at Maka Dai Dai Shogi, though: this uses the same Emperor (except that you can only get it through promotion). This says:
The Emperor is a Universal Leaper: it can move to any square of the board. It cannot capture enemy pieces that are protected, though. That even holds for capturing the opponent's last royal. Protected here means that the Emperor could have been recaptured if the opponent would have been allowed to play on without royal.
In FIDE a King cannot capture a protected piece, but it can capture a protected King, so it is illegal to put it next to your opponent's King even when protected. For Emperors the opposite holds: you cannot capture a protected Emperor with it. (This difference is due to the after-move, and in the description of the Emperor I elaborate on the initial statement in terms of such an after-move.) Note that the historic rule descriptions of these games are very minimal. So it is not really known if the ban to expose your Emperor to capture is for every move, for every capture or just for capturing the opponent's last royal. Because no one in his right mind would ever even consider exposing his Emperor to capture if it would not be for the purpose of instantly winning the game or taking out the opponent Emperor, they don't waste words on it. Were the game to continue, being an Emperor behind means a certain loss. Also, Shogi is usually played under the rule "illegal move = loss", as opposed to FIDE, where "illegal move = take back". So it is completely pointless to make extra rules that make losing moves illegal in Shogi.
Anyway, this ignores the main point: the purpose of the glossary is to clarify matters by assigning unique meanings to concepts that universally apply. Not to promote confusion by making the definition of a term context dependent, possibly in an undesired way. If a term is ambiguous because its meaning depends on context, its use should be discouraged. If we describe such terms, it would be wise to accompany those with a warning like:
The meaning of this term is context-dependent, and to minimize confusion due to incorrect interpretation of the context, it should not be used in rule descriptions.
I don't think so. The Emperor does have a pseudo-legal move to that square. That it cannot use it is just because it would expose itself (the royal) to capture, just as moving a pinned piece would.
Thank you for this example. It shows we are not talking about the same thing. What you're calling pseudo-legal is a convenient shortcut for distinguishing what is easy to compute from what takes more time to compute. What I'm talking about is a conceptual difference between a piece's own powers of capture and the universal restriction on all pieces against creating an illegal position. In the case of the Emperor, its inability to capture on a protected space may require more computation than usual, but it is an inherent part of that piece's ability to capture. So, conceptually speaking, regardless of how you choose to program it, the ability to move to an unprotected space is not included in its powers of capture. If you claim that it has a pseudo-legal ability to capture on a protected space, then this shows that pseudo-legal is not a useful concept for describing what attack means.
Also, having read the relevant parts of the Tai Shogi rules, the reason behind the restriction is to prevent the first player from taking the opponent's Prince or Emperor on the very first move. Unlike most Chess variants, this game has two royal pieces, and it is legal, though not usually advisable, to leave a Prince or Emperor exposed to capture. The Wikipedia page mentions that a player could choose to sacrifice one of his two royal pieces in a gambit. Although the Emperor may not capture on a space where it would be under attack, it is allowed to move to an empty space where it would be exposed to capture. The Prince moves like a King, but it is also allowed to move into or remain in check. So, the restriction on the Emperor's ability to capture is not because it would create an illegal position like moving a pinned piece would.
H. G. Muller wrote on Mon, May 4, 2020 02:53 PM UTC:'Illegal position' is not something that is defined in the FIDE rules, or anywhere else I am aware of. There just are illegal moves, and those are moves that violate at least one game rule. You could of course define an illegal position as the position that arises from an illegal move, but they are not always recognizable: if I start a FIDE game with 1. Nxh8 that would definitely be an illegal move, but the same position could also have been reached through legal moves, so it cannot be an illegal position. Castling through check or out of check is an illegal move in FIDE, but the resulting position can be fine.
There is a universal restriction on all pieces to not make illegal moves. That is what 'illegal' means. What actually is legal and what not depends on the detailed game rules. In some games it is illegal to castle when your King is attacked, in others it it is illegal to capture a Lion with a Lion when the latter is protected, in some games it is illegal to capture an Emperor with an Emperor when the latter is protected. In some CVs it is illegal for Kings to stand next to each other, in other CVs there is nothing against it, or they are not even allowed to face each other from a distance. There is nothing universal about that.
So no, I don't think we are talking about different things at all. Pseudo-legal moves are moves that a piece has considering the occupation of the departure square, target square and possibly the squares along the path that it is supposed to take to get to the latter. Like in move diagrams. What is on the board outside the path taken in one of the possible moves has no effect on the pseudo-legality of the latter. (Even if it is in the path of other moves the piece might have!) For an orthodox King the pseudo-legal moves would be the adjacent squares not occupied by a friendly piece, for an Emperor it is the entire board except squares occupied by friendly pieces. (There is no path, as it is a leaper, so the pseudo-legality of each move only depends on the departure and destination square, just as with the King.) There just are some additional game rules that might cause a pseudo-legal move to be in fact illegal, such as that you cannot go there if the the square is under pseudo-legal attack, unless the enemy King is on it. Or that you cannot go there if the square is under pseudo-legal attack and there is an Emperor there.
The rules for game-terminating moves can seem different from what they are in the pre-termination part of the game, e.g. after a King strolls into check (illegal!) you are allowed to capture it with a pinned piece, while during the game that would never be possible. But that doesn't mean they have to be different in a universal way. Each CV can specify its own rules for the after-moves. In fact the difference with the pre-termination rules can often be made to disappear by just having rules for the number of after-moves granted in various situations ('normal' move, capture of royal, baring a royal, reaching a goal square). But then that number of after-moves can arbitrarily vary from CV to CV, there is nothing universal about that. And a different number of after-moves translates into seemingly different rules for the (after-)moves that preceded them.
We are spending way too much attention on Tai Shogi, which was just one example (and because of its multiple royals, a rather complex one). Better focus on Recursive Chess, where King capture is not legal when it exposes your own King to capture on the next move.
So no, I don't think we are talking about different things at all. Pseudo-legal moves are moves that a piece has considering the occupation of the departure square, target square and possibly the squares along the path that it is supposed to take to get to the latter.
None of the dictionary definitions for occupation in Merriam-Webster fit your use of the word here. I suppose you're trying to refer to the pieces occupying those squares. So, let's rewrite this as
Pseudo-legal moves are moves that a piece has considering which pieces are on the departure square, the target square, and possibly the squares along the path that it is supposed to take to get to the latter.
Consider a royal Dragon King in Fusion Chess. It has the Rook's move, but it cannot move through check. Whether or not a space it may cross over is checked will depend upon what is on other spaces than those you just named. So, by the definition you gave here, it has the pseudo-legal move to capture exactly as a Rook does.
As I was writing this, I decided to test this out in both Zillions-of-Games and Game Courier. I did the same series of moves in both, creating a situation where a White Dragon King was on the same file as a Black Paladin with nothing in between them, but there was an intervening space covered by a Black Rook. In Zillions-of-Games, the Paladin could not split apart, because the code considered it attacked by the Dragon King, but in Game Courier, it could split apart, because the code recognized that the Dragon King could not pass the Rook's rank to capture the Paladin. This is a matter I hadn't thought about before, and I'm going to have to make a decision about how it works. I'll begin with an examination of the code for each to determine how easily one or the other could be changed. In this game, attacks by one royal piece against another are allowed even across checked spaces, but captures by royals of non-royals are illegal if the royal piece has to move through check to complete the move. I could say that the royal piece can make impotent attacks against non-royals, and these are enough to stop them from splitting apart, or I could rule the other way. There is some leeway about what to do here, and I will get back to this discussion after I look into that.
Greg Strong wrote on Mon, May 4, 2020 07:08 PM UTC:In Zillions-of-Games, the Paladin could not split apart, because the code considered it attacked by the Dragon King, but in Game Courier, it could split apart, because the code recognized that the Dragon King could not pass the Rook's rank to capture the Paladin. This is a matter I hadn't thought about before, and I'm going to have to make a decision about how it works. I'll begin with an examination of the code for each to determine how easily one or the other could be changed.
I think as a general question of creating a chess engine to play this game, the far simpler option is for the paladin to not be able to split apart. The dragon king can reach the paladin by a pseudo-legal move. This is a simple (linear) determination. To go the other way, it becomes a recursive problem. ChessV could do the first pretty easily. The second option would be difficult at best and maybe borderline impossible (at least without violating the architecture's separation of responsibilities.)
I couldn't find a way to make Zillions-of-Games do it differently, but I found a simple solution to making Game Courier do it differently. So, I went with the interpretation enforced by Zillions-of-Games, updated the fission-attacked subroutine, and updated the rules for Fusion Chess.
H. G. Muller wrote on Mon, May 4, 2020 09:33 PM UTC:So, by the definition you gave here, it has the pseudo-legal move to capture exactly as a Rook does.
That is correct, and intended. Rules about passing through check are on par with rules about moving into check. It is often easiest to interpret passing through check as exposing the royal to (generalized) e.p. capture. The latter kicks in when a pseudo-legal move is defined as 'composite' rather than 'monolithic'. (I make these terms up as I go...) There then is an extra rule that in the next turn the opponent has the right to partly retract an immediately preceding composite move before making his own move, provided the latter captures the moving piece (perhaps only with a sub-set of the piece types). In orthodox Chess the Pawn double-push and castling are composit moves, and the opponent can make the doubly-pushed Pawn go back to the square it passed through, and capture it there in the normal way (but only with a Pawn). After castling, he can 'uncastle' to the point where the King has made the first step, and then capture the King there with any piece. With as a result that the castling was illegal, as you are not allowed to expose your King to capture.
Passing through check, like for the Caissa Brittania Queen, could work the same. The pseudo-legal move does pass through check, but it is composit. If an actual move would pass through check, the opponent would undo it to the point where the Queen was in check, and capture it there. (Again any piece type could do this.) Thus demonstrating that the move that passed through check exposed the Queen to capture, and thus was illegal. The necessary condition, however, is that the opponent should get to move again. If there is no after-move after capturing a royal, Q x Q could pass through check safely. The possibility to recapture e.p. is worth just as little as the possibility to recapture in the ordinary way, when you lost your royal.
If in Fusion Chess the right to split up depends on being attacked, and there are pieces that are not allowed to pass through check, it is up to the designer to decide if the splitting rights are derived from pseudo-legal attack, or from legal attack only.
I had a similar dilemma in Mighty Lion Chess. I wanted to have the Chu-Shogi rule that Lions cannot capture protected Lions in a Chess-like game (that has checking rules). For simplicity I decided that pseudo-legal protection would be enough. Which is equivalent to saying that there is no after-move when a Lion that just captured a Lion is recaptured. So you don't have to worry about exposing your King in check when recapturing that Lion, it is immediately decisive, just like when you capture a King. This rule makes the Lion effectively a second (absolute) royal for one turn after Ln x Ln.
To comment on Greg's point: Fusion Chess (old rules) would be double complicated, because the legality involves not only exposure of the royal, but also has to take account of whether it passed through check. The latter is already a pain in itself, because you would also have to test all the square on the path of the royal after it moved, not just where it is now. Probably testing this afterwards, as my engines do for normal King exposure, is no longer efficient, since many moves of the royal might all pass through the same check. Same for the split: all moves of the parts would become illegal together when you detect an attack. I guess you ccould exploit the null move here very well: if every node in the full-width search starts searching a null move, the move generation for the null-move reply would detect all pseudo-legal attacks on fused pieces. And even when the null move drops you directly into QS, you would search these moves, since these are all captures. In that QS any captures by royals would have to be vetted for not passing through check, and they could return the score for 'illegal move' when they do pass through or move into check. The null-move could then discard those pseudo-legal attacks. Only problem is that when you get a beta cutoff, you know that the null move has failed low, and thatthe parent node will now have to do a normal search. For which it has to know the legality of all the splits. So you would be forced to search all captures of fused pieces in the null-move reply, even after beta cutoff. (Or at least judge their legality, which probably requires making them.) That is, as soon as you have found one legal capture on a fusion piece, you can ignore all other pseudo-legal captures on it if the score is already above beta. In the end you would know which fusion pieces are under legal attack, pass that info back to the parent, who would then use it during its move generation. As I understand that you cannot capture with a split, there is no splitting in QS, and it doesn't matter that you don't search null moves there.
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What the two versions of Fusion Chess taught me is that there are multiple ways of handling complications due to multiple pieces being affected by being attacked. With that in mind, I propose keeping the definitions of attack simple but adding a footnote for the complications that may arise in some games. So, here is what I propose: 1. A piece is attacked (or under attack) when the opponent has a piece that could legally capture it on his turn.* 2. A space is under attack for a particular piece when moving there without any other changes to the position would allow an enemy piece to legally capture it on the next move.* 3. Colloquially, "to attack" can also mean to play a move that creates one of the above situations. * In games in which multiple moves are allowed or in which the state or threat of being attacked affects the movement of multiple pieces, the determination of whether a piece is attacked can become less straightforward. When this happens, it is up to the designer to spell out in detail what does and does not count as an attack. |
H. G. Muller wrote on Tue, May 5, 2020 10:30 AM UTC:I am still a bit worried about the second definition, for the case when the square in question is already occupied in such a way that moving there would mean capturing our own piece. Someone might interpret it as "but you cannot move there, so it is not under attack". Of course in that case the piece already on the square will usually be under attack. (But not if there is a type-discriminating attacker.)
I still would think it would be good to mention that attacks can also be pseudo-legal (if explicitly labeled such), with basically the same definition instead that 'legal capture' in that case would be replaced by pseudo-legal capture.
Some more thoughts about pseudo-legal moves: in complex cases it could be murky what you consider the 'path' taken by the piece. For simple sliders or hoppers this is of course obvious. Even for bent hoppers that change direction on or behind their mount the path is intuitively clear. But Mats Winther has designed some 'bifurcator pieces' that would change direction on the square before they collide with an obstacle. The obstacle then doesn't seem to be in the path, (although it is definitely in the path of other potential moves), and the bifurcator doesn't seem to hop. But yet the obstacle affects the move. The situation could be rescued by the interpretation that the path actually does go over the obstacle, turns 90-degrees (say left) there, and immediately after stepping off the obstacle, 45-degree right again. Then it would actually be a hopper ('crypto-hopper'?), with a straight first-leg, but a bent second leg at an angle.
It is even worse for 'deflecting' sliders, which would bend their trajectory 45 degrees when the square perpendicularly next to a square they are passing through is occupied (and on the opposit side empty), in the direction of that occupant. There the 'zone of influence' is not just the path where the slider could be blocked, but also all squares lying next to it. Still only a sub-set of the board, but it starts to be uncomfortably large.
The worst I could come up with was a variant 'Gravitational Chess', where sliders do not move in straight lines, but every time they pass next to a piece experience its gravitational pull and change direction. If they pass between two occupied squares, the gravitational pull cancels, and they keep going as they went. This arbitrary many times.
The Rook here could move g1-g2-g3(2P cancel)-g4-f5(P)-e5(N)-d4(N)-c3-b3(wP)-a4(wP)-a5(bP)-b6(bP)-c7-d8, with in parentheses the piece that deflects it to that square.
Depending on the actual position, a piece in this CV could have any trajectory. It is like a Tenjiku-Shogi area move of arbitrary many King steps that can arbitrarily change direction for every step. One could say all King tours through empty squares ending on an empty square or opponent are pseudo-legal. But only a very small fraction of those would be legal, depending on whether they make the right bend when they pass next to other pieces.
I didn't follow your example concerning Gravitational Chess. It appears to be a different game than Neto's Gravity Chess, and all we have on it is a Java applet by Ed Friedlander, which are not supported in recent browsers. I think we have to bear in mind that the purpose of a glossary is to quickly and clearly explain the standard meanings of terms to people who are unfamiliar with them. It is not to give a comprehensive and scholarly account of the subject. We might create pages for some terms that cover them in more depth, as Greg has for castling, and I've been thinking of doing this for the related concepts of attack and capture. For the glossary definition, we should aim for clarity, brevity, and conformity with standard usage. Inclusivity is also good, but we don't need to stretch a definition so much that it will work with every game we can think of. I've had some thoughts on how to make the definition of attack briefer. Here is the entry I now propose. It also includes a separate paragraph for examples of different kinds of attacks. I have also included entries for some related terms.
attack - 1. n. The threat of capture of a piece on its current space, on a space it may move to, on a space it may pass through while making a move, or on an intervening space while making a leap.
The first two types of attacks are common in most Chess variants, including Chess, Shatranj, Xiangqi, and Shogi. The third comes into play in Chess when a pawn may be captured en passant or when the king is not allowed to move through check when castling. Other examples of it may be found in Caïssa Britannia, whose royal queen may not move through check, and in Fusion Chess, which also has royal pieces incapable of moving through check. The fourth is found in Metamachy, which allows the king to leap two spaces on its first move, though not over checked spaces, and it is illustrated in Fusion Chess, whose cavalier king may leap as a knight but not through check.
2. v. To threaten a piece with capture in any manner described above.
3. v. colloquial. To make a move that creates a new attack on an enemy piece on its current space.
attacked, under attack - 1. adj. Subject to attack; threatened with capture.
check - 1. n An attack against a royal piece.
2. v. To attack a royal piece.
checked, in check - 1. The state of a royal piece being under attack.
I've been thinking that we could have a terms directory, in which the index would be a glossary of terms, and other pages in the directory would be pages that treat certain terms in depth. Having this would allow us to build a new glossary while leaving this one intact, which would be useful for comparing them until the new one is finished, and when it is, I could redirect URLs from this one to the new one.
I have started working on a new version of the glossary at www.chessvariants.com/terms/. I have been working on updating the HTML to use logical formatting instead of physical formatting and to be easier to read when editing the page. I have changed, added, or deleted some definitions, though I'm not focusing on that quite as much until the HTML is fixed up. When I have deleted a definition, I have usually moved the anchor tag to a related definition. Some definitions never had anchor tags, which means no one ever linked to them. I have sometimes deleted a term with no anchor tag altogether.
The main part of updating the HTML on the new page is done.
I at first thought a line piece was the same thing as a rider, but the definition for pass-through square suggests that the Xiangqi elephant is a line piece. But then what about the Xiangqi horse, which doesn't move in a line? What is the origin of the term line piece, and what is it supposed to mean exactly?
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John William Brown created this page 20 years ago, and he wrote on it
It has been longer than that, and it's about time we updated the glossary. The original purpose behind the glossary was a good one. We need a common vocabulary for speaking about Chess variants, and we need a common reference for that vocabulary.
Brown drew from multiple sources to build this glossary. We all have access to this site, which is one of them. I own copies of the books by Pritchard and Dickins. All I'm missing is Brace's book. If there are other resources we can draw upon, please mention them in a comment.
In updating this project, I aim to
However you think you may help, please do. You may post your thoughts and ideas here as we go about this.