Comments/Ratings for a Single Item

I received the following email:

"I just wanted to bring to your attention an error on the Ultima variant page: Ultima (chessvariants.com)

In the "Object of the game" section, the word "checkmating" should be changed to "capturing" (so the line says "capturing or stalemating"). This variant is intended to be played without checkmating; you are meant to capture the enemy king. This is an important aspect of the game, because a common strategy is to misdirect the opponent into opening their king up to an attack in order to capture their king on the next move. The threat of losing to a "sneak attack" was specifically mentioned by Robert Abbott when he published the rules.

For citations: Ultima was first published in Robert Abbott's book "Abbott's New Card Games" in 1963. On page 125, when detailing the rules of Ultima, Abbott wrote "The object of the game is to capture the enemy king."

This webpage was written by Robert Abbott 41 years later, in 2004: http://www.logicmazes.com/games/puz1to4.html He writes: "In Ultima the object is to capture the king, not achieve check mate." This is what the page said when it was published by Abbott in 2004, and it has remained unchanged since.

I hope this information helps. Thank you for your time."

A quick check of the references shows the above is correct. I started a more extensive search, but haven't found anything else yet, except the discrepancy noted below. Currently I've started looking through the 150 comments on the game's onsite page. If I find anything other in the search, I'll post it here.

Abbott himself recommended the chessvariants page for the best explanation of the game. From Abbott's logicmazes.com page:

"After my card game book was published, I began seeing problems with Ultima and tried to fix one of them by making a change in the rules. These revised rules appeared in the 1968 paperback edition of the book. The change turned out to be a pretty bad idea, and everyone uses the 1963 rules instead.

For the best explanation of the rules (the 1963 version) see this page of the web site ChessVariants.org. Not only is their explanation well-written, but if you click on “Animated Illustration” you’ll see a series of moving diagrams that help explain the pieces (a sample is at the right). These are animated GIFs created by David Howe. They are a fantastic innovation for presenting game rules and could be used in other forms of technical writing. The Chess Variants site also has an interview with me."

in Ultima the object is to capture the king, not achieve check mate.

Since it's on Abbott's page, that gives it authority. But I should do some more checking, as Pritchard said "The object remains checkmate," and I'm aware that Abbott tried to revise Ultima, but the original version remained more popular.

In my research, I learned that Robert Abbott died in 2018. To confirm the 1963 rules once and for all, I have ordered a copy of his book.

I wrote this in 2004:

The Wikipedia page on Baroque Chess currently asserts that Robert Abbott did not invent the game, as can be discovered by reading the Fairy Chessmen by Lewis Padgett. I expect this is a bunch of nonsense and have explained why in the discussion area for Wikipedia's Baroque Chess page. However, I have not read the Fairy Chessmen and cannot get ahold of a copy.

Since then, I have read The Fairy Chessmen by Lewis Padgett, which was a penname for the husband/wife team of Henry Kuttner and C. L. Moore, and it does not describe Ultima. It does show a knowledge of fairy chess and mentions some pieces, such as the nightrider and the grasshopper, but it is a science fiction novel and does not delve into the subject too much. Since I have it on my Kindle, I searched for the names of Ultima pieces and did not find any except the king.

Just stating that one wins by capturing the king doesn't fully cover it, as stalemate can be achieved by immobilizing a bare king. Assuming that removing one's own king is illegal. As I don't think removal of own pieces is covered by the term 'capture', the rules should either explicitly state king removal is terminating the game as a loss, or it would have to be specified that stalemate is a win. Which, together with king capture as winning condition implies that checkmate is a win. Assuming that none of the players will ever be so stupid as to overlook he can capture the king.

BTW, 'stalemating the opponent king' is a non-sensical phrase: the concept of stalemate applies to a player, not to one particular piece of a player.

Also note that when level of play is so low that players are likely to blunder away their King in a single move, invoking concepts like checkmate becomes a bit pointless, as they would not be able to recognize a checkmate with any accuracy. This becomes more an issue of how to handle illegal moves, which I do not consider so much part of the game rules, but more 'tounament etiquette'. Even orthodox Chess is often played with 'blitz rules', where an immediate win can be claimed after an opponent plays an illegal move, rather than forcing a takeback and resuming the game from there. So king-capture victory can simply be seen as a method for claiming a win after violation of a checking rule. The important issue from a game-theoretical perspective is how to handle stalemates.

As you are currently revising the page for this important game, maybe you could do something about the graphics. There are 4 different graphic sets used in this page and this is a lot. It doesn't help.

This page is indeed in a sorry state. With JavaScript switched off the Interactive Diagram does not appear, and we get to see a number of non-functional buttons with the Diagram's definition displayed below it as reformatted text. People then only get to see the static image of the setup in the Alternate Pieces section, plus two static move diagrams, which uses a hitherto unintroduced and far from self-explanatory piece representation.

In fact it is strange that these move diagrams are on the page at all; none of the other pieces have such move diagrams, and all piece descriptions already refer to a page with animated move diagrams. Note that separate move diagrams are not really a luxury here even for people that can see the Interactive Diagram, as the capture mode of some of the pieces is not properly demonstrated by the move diagrams that by default can be displayed through this Diagram: it would show moves of the piece on a board that is otherwise empty except for a single opponent 'pawn' that can be moved around through hovering over the board. Pincher Pawns, Chameleons and Coordinators never have any captures under those conditions, but the Withdrawer is one of the few pieces for which the Interactive Diagram would work (if JavaScript is switched on).

I see no logic in having a separate page for move diagrams, no matter how revolutionary these were at the time of their publishing. Move diagrams belong in the piece section of the article describing the variant, and the page with the move diagrams would make an excellent Pieces section for this article.

I also see no reason to show an Alternate Pieces section if there already is a (working) button through which the Interactive Diagram can show this same, as well as several other alternate representations. So this section should be hidden when JavaScript is switched on. And with JavaScript off the setup should be shown not only in the 'alternate' representation, but also in the preferred one. A more logical layout would be to delete the section, but show the diagram side by side with a static image of the setup with ordinary chess pieces (and inverted Rook) in the Setup section.

As to the piece sets that can be shown through the buttons: is it really needed to include the 'Alfaerie Animals' representation? Showing multiple representations can only increase confusion. It should be obvious that chess pieces can be represented by any set of images, and one can even buy orthodox chess sets where all pieces are sheep, frogs, pigs or heroes and villains from Star Wars. Is anyone actually using this 'Alfaerie Animals' representation? If not, why would we encourage this particular choice over the few million others that could be concocted with animal images from the Alfaerie set?

I also seem to recall that originally the initial (static) setup diagram used the ('small') Utrecht theme with the 'inverted-Rook representation'. Now that Utrecht is available in SVG and 50x50 PNG I think it would be better to use that rather than Alfaerie to present this representation as the primary diagram, and only show 'Ultima-Alt', 'Alfaerie Queens' and 'Abstract' as alternatives.

Now that Utrecht is available in SVG and 50x50 PNG I think it would be better to use that rather than Alfaerie to present this representation as the primary diagram, and only show 'Ultima-Alt', 'Alfaerie Queens' and 'Abstract' as alternatives.

I disagree and have changed it back to using Alfaerie.

I see no logic in having a separate page for move diagrams, no matter how revolutionary these were at the time of their publishing. Move diagrams belong in the piece section of the article describing the variant, and the page with the move diagrams would make an excellent Pieces section for this article.

Now that you have moved the animated diagrams to this page, I see the logic to keeping them on a separate page. Animations on a page are annoying, which is why <BLINK> is no longer part of HTML. Also, animated diagrams are not suitable for printing should someone choose to print the page to have a copy of the rules. It's better to provide static diagrams, as I was starting to do before I got sidetracked by other things. Anyway, I was able to get a cached copy of the older version of the page. So, my work on the static diagrams has not been lost.

Well, there was never a danger of anything getting lost, as I was careful enough to first make a copy of the old version.

Because I was not done yet editing the page before I saw your comment, saving my latest changes probably overwrote whatever you did.

Note that the old page contains many errors and unclarities. E.g. the starting squares mentioned for the pieces did not coincide with that in the diagram.

If there are to be static move diagrams, they should not be made with the Abstract piece set. For people with JavaScript off these pieces have not been introduced; they would only be aware of the 'inverted rook' or ultima-alt representations, so the move diagrams would be useless to them.

Is anyone actually using this 'Alfaerie Animals' representation?

As far as I'm aware, not for Ultima itself (even the GC preset lacks it as an option), though some of its offshoots (Rococo, Fugue) and other games using its pieces (Carlos Cetina's Universal Chesses) use its Chameleon, Long Leaper, and Immobiliser quite consistently. Those games use a different image for the Withdrawer though (An ox, whereas the one here is used by David Howe for his Chess on a Longer Board with a few Pieces Added) and don't feature the Coördinator at all

Whether use in other games qualifies the piece set to be used on this page too is another question of course (though one could certainly argue for at least the GC preset to include them as an option)

I have now finished the new diagrams for this page, and I have updated the piece descriptions, mostly by copying and modifying descriptions I already wrote for Game Courier. But I also checked the other descriptions to make sure I wasn't missing any important details.

If there are to be static move diagrams, they should not be made with the Abstract piece set. For people with JavaScript off these pieces have not been introduced; they would only be aware of the 'inverted rook' or ultima-alt representations, so the move diagrams would be useless to them.

I have also updated the setup diagrams. I moved the ultima-alt diagram to the page for the animated diagrams, and I added two diagrams that show up when JavaScript is disabled. One uses the Alfaerie Chess pieces, and one uses the Abstract pieces. They will also show up in the printed version.

is it really needed to include the 'Alfaerie Animals' representation? Showing multiple representations can only increase confusion. It should be obvious that chess pieces can be represented by any set of images, and one can even buy orthodox chess sets where all pieces are sheep, frogs, pigs or heroes and villains from Star Wars. Is anyone actually using this 'Alfaerie Animals' representation? If not, why would we encourage this particular choice over the few million others that could be concocted with animal images from the Alfaerie set?

This set was in the sets directory for Game Courier, and I didn't realize until today that it wasn't showing up in Game Courier. So, I have now corrected this. Although the images it uses are not all available as SVGs, I consider it the best Alfaerie set for Ultima, because the images are distinct from each other while also suggesting the powers of each piece. The Alfaerie Queens set slows down my recognition of the pieces, because they look too similar, and the Alfaerie Chess set uses pieces that mostly do not suggest the powers of each piece, as the piece designs used were not intended for Ultima.

Well, I would easily know a better set that would have very diverse shapes and be more suggestive of the powers:

• Pincher Pawn -> Go stone
• Long Leaper -> Draughts King (i.e. stacked chips)
• Chameleon -> Mirror
• Coordinator -> Radio-telescope dish
• Immobilizer -> Horseshoe magnet
• Withdrawer -> Rocket

So if we are bent on introducing new sets that have never been used before, we better give it some thought before acting rashly. We are not married to Alfaerie, so "best set using Alfaerie pieces" is a meaningless distinction. That a piece set has dedicated Ultima pieces would be a reason to show them 'under a button', but if they are not much good we should avoid their use (and thus the use of the set they belonged to). Beside that, we should just present the set that is best without limiting ourselves to existing images from existing sets.

So if we are bent on introducing new sets that have never been used before, we better give it some thought before acting rashly.

A variation on the Alfaerie Animals set has long been in use for Rococo, which is based on Ultima. Since it appears that the Alfaerie Animals set has not been in independent use, I have replaced its Withdrawer image with the ox image used in Rococo. This also brings it more in line with the Galactic set, which was the default set for the original Game Courier preset, as that set uses an ox for the Withdrawer and a Kanagaroo for the Long Leaper. Also, its Pincer Pawn image matches the image used for another Alfaerie set that has long been in use on Game Courier. What I think happened is that David Howe made the Alfaerie Animals set first, and then he later designed other pieces for Ultima and replaced that set with the new set.

Each of the other sets has long been in use or is similar to one that has been. The Alfaerie Chess pieces have long been used for other variants. Judging by Archive.org records, I had created my Abstract pieces for Ultima by early 2004. I have long made them available on Game Courier, and they are now the default for the new Ultima preset. David Howe's Ultima-Alt set was previously used on this page and is still used on the animated diagrams page. And your Alfaerie Queens set is a variation on David's most recent Alfaerie set for Ultima, which has long been available on Game Courier, but it differs because some of the images in that set have not been converted to SVG yet.

So, the copy of Abbott's New Card Games that I ordered turned out to be the 1968 edition. When I looked at the record of my Amazon order in hopes of complaining about this, it said it was the 1968 edition. Checking ebay, I saw another copy with the same cover described as the 1963 edition, and maybe that is why I thought this would be the 1963 edition. As David previously reported, this edition limits the distance a piece may move to the rank it is on from that player's perspective.

Getting to the question of whether the game is won through capture or checkmate, here is what it says,

The object of the game is to capture the enemy king. The players declare check in a fashion similar to that of Chess. That is, if a player makes a move that puts him in a position to take the enemy king on the next move, he announces check. A player may not move into a position that puts his own king in check.

The game is won when a player achieves checkmate, attacking the enemy king in such a way that it cannot escape capture on the next turn. A player also wins if his opponent is unable to move any of his pieces.

Although he first seems to say that it is won through capturing the enemy king, the sentences I have put in boldface make it clear that the game is won by checkmating or stalemating the opponent, and as a player may not make any move that places (or presumably leaves) his king in check, any position where a king could actually be captured is illegal.

It turns out that Abbott has included a copy of the original 1962 article on Ultima on his website, and I have now added a link to it. Here is what it says on the object of the game:

KING: The king moves and captures in exactly the same fashion as the chess king. The object of the game is to capture this king. The same rules for declaring check apply as in chess.

One could get the impression from this description that the object is just to capture the king, as this does not explicitly mention checkmate or stalemate. If Abbott was referencing this version of the rules, he could have misremembered the object of the game. Since a change in object has not been mentioned as one of the changes between the 1963 and 1968 editions, I am assuming until I learn for sure otherwise that the 1963 edition specifies checkmate and stalemate as the winning conditions. Also, if it "moves and captures in exactly the same fashion as the chess king," it could not move into check.

I think it is hard to argue against "The object of the game is to capture the enemy king." This is a direct quote from Abbott. There's no way to misinterpret that sentence to mean the object is checkmate.

From what I see, both the oldest source and newest source from Abbott agree on this. Even if the 1968 edition (which Abbott is on record disavowing by the way) includes contradictory language, it still says "The object of the game is to capture this king." This statement can't be ignored.

These statements are very straightforward and impossible to misunderstand. Every source from Abbott is in agreement. In each source, the object of the game is explicitly stated to be "to capture the king."

I believe "The object of the game is to capture the enemy king" makes it clear what the object of the game is, and there is only one way to interpret it. Even if some of these sources include contradictory language that also states the exact opposite, not all of them do (i.e. the rules as explained by Abbott on his website state that the object is to capture the enemy king, and they also specifically state that there is no checkmate). The only object every source from Abbott includes and agrees on is "to capture the enemy king."

Also, if it "moves and captures in exactly the same fashion as the chess king," it could not move into check.

I feel this may be a bit of a stretch. This interpretation would contradict the object of the game that is explicitly stated in the same line. Rather than assume Abbott was thinking of checking behavior and castling when he said the king "moves and captures" as the chess king does, it would probably make more sense to read his statement literally: the king "moves [1 square in any direction] and captures [by displacement]" as the chess king does. Taking his sentence at face value has the added benefit of not contradicting his very next sentence in the paragraph as well.

Even if there was a source in the past where Abbott indicated "the object is to capture the king" and at the same time he said "the object is to checkmate the king," that only tells us one of those contradictory statements would have to be wrong. Given that Abbott wrote an in-depth explanation about the object of Ultima on his website, it seems clear which option he intended to go with.

I am looking at this page mentioned earlier, and Abbott is even more explicit here.

The first puzzle is Mate in 1 and all the others are Mate in 2. This follows the conventions of chess problems, even though in Ultima the object is to capture the king, not achieve check mate. So, Mate in 1 should be translated to Capture the king in 2 moves (that is: White moves, Black moves, then White moves and captures the king). Mate in 2 translates to Capture the king in 3 moves.

Note that if checkmate was the object of Ultima, there would have been no reason to include a paragraph here at all. Attempting to find checkmate is how these types of puzzles work by default. Abbott went out of his way to write and include this paragraph about how the object of Ultima is not the same as chess, and to make it completely unambiguous. It's pretty clear he didn't want any further confusion about this.

Going through the content of Abbott's explanation, I'll start by highlighting the short answer:

in Ultima the object is to capture the king, not achieve check mate.

In this case, he not only said "to capture the king" is the object of the game (matching his other sources), but this time he even elaborated that achieving checkmate is not the object of the game. This explanation directly addresses the contradiction that was found in one of the older sources and leaves no room for misunderstanding.

However, in case he still hadn't been clear enough yet, Abbott went on to explain the actual turn sequence that ends a game of Ultima:

White moves, Black moves, then White moves and captures the king

Note that in Abbott's example of how an Ultima game ends, Black makes a legal move that leaves his king under attack. It is obvious from this that there is no checkmate, otherwise Black could not have moved. Abbott's detailed move-by-move explanation removes all ambiguity and clears up any potential confusion. It rules out any possibility that checkmate is the intended object of the game.

On the Chess Variants article, there is also a 4th source linked, the original 1962 Article introducing the game. This article was brought up earlier, but again, this source matches the rest of them, clearly stating "The object of the game is to capture this king." The rules include no mention of checkmate at all. All it says about checking is "The same rules for declaring check apply as in chess." Of course, there are no rules that require you to declare check in chess, so that's a moot point.

Additionally, I see on Abbott's site that he was really enthusiastic about David Howe's "extensive" and "especially useful" write-up of an Ultima game ending. I found his write-up.

These are the last three moves of the game in his write-up:

White Chameleon at e8 moves to g6

Black must move LL at g7 (or suicide a piece)

White Chameleon at g6 captures Black K

Note that in this write-up, White moves a Chameleon next to Black's King, which Black has no way to avoid. Black is then required to make another move. White then captures Black's King to end the game.

This is another specific example for how an Ultima game ends, with Black making a move that ends with his king under attack, and White then capturing Black's king.

Earlier it was mentioned that Abbott recommended the chessvariants page at one point, but he did so in the context of wanting to share admiration for David Howe's animated illustrations. It appeared to be a short respectful way to introduce the topic, giving a general compliment lacking any specificity. Based on the rest of the paragraph, Abbott makes it clear that the part of the site's explanation he was impressed with was the animated illustrations that explain the piece movements. Even if all the context is ignored in order to assume the compliment was well-researched and literal, saying something is the best option available doesn't suggest that it can't be improved upon, or that the speaker made a point of proofreading the site in the first place.

Additionally, shortly after that paragraph where he says chessvariants is a good site, he then links to his own page which he had just written himself, where he states multiple times that the object of Ultima is to capture the enemy king, and that the object of Ultima is not to checkmate, and he even explains move-by-move how an Ultima game ends in order to make the object of the game perfectly clear.

Actually... Abbott mentions multiple times, across several different pages, that his Ultima puzzles (which required you to capture the enemy king) were created in 1964. This means the 1963 rules, which these puzzles were utilizing, also intended for you to capture the enemy king.

With the Abbott of 1964 and the Abbott of 2004 being in agreement that the object of Ultima is to capture the king, the conclusion seems pretty straightforward.

Well, many people would say that the object of chess in general is to capture the enemy king. So I don't think such a statement in the description of Ultima necessarily means anything other than that it is similar to chess in terms of goal, rather than to eliminate all opponent pieces, reach a certain goal square, etc.

The thing of practical interest is whether there is a checking rule, which would make this king capture a hypothetical event one move after checkmate. Note that Shogi is generally considered a king-capture game, and that the rules still refer to checkmate (in the context that this should not result from a Pawn drop).

In cases where stalemate is a win, it is a moot point anyway. The only practical issue is what should happen on an unforced king sacrifice: does the player lose through having made an illegal move, or should he take the move back and play another? It seems that Abbot suggests the latter.

I don't believe many people would say "in Chess the object is to capture the king, not achieve checkmate." I don't think anyone would say that. But that is what Abbott said about Ultima, as a direct quote.

The extra clarifying statement he added at the end ("not achieve checkmate") specifically denies the possibility that he meant "this is equivalent to checkmate."

If the rules of Chess stated "in Chess the object is to capture the king, not achieve checkmate" then that is what would happen. Players would likely still resign before the game is over, as often happens now, but someone determined to play the game to completion would have to get the enemy king off the board to win. I think the wording that was used makes this very clear.

The examples Abbott laid out show that even when the king is guaranteed to be captured on the next turn, play still continues with both players moving normally. If the "winning" player doesn't perform the capture, then they don't win, and the game would continue until one of the kings was captured.

It seems that Abbot suggests the latter.

Could you elaborate on this? Apologies if I'm overlooking something, as I may have parsed through everything Abbott has ever written at this point, and it's a lot to keep track of.

From what I've seen, in all 4 instances where Abbott published an explanation about the rules of Ultima over the span of 42 years, he has always said you can capture the enemy king directly. In none of them does he suggest you're allowed to undo this outcome if it resulted from an illegal move, nor does he otherwise imply you have the right to redo moves without consequence. Again however, if I've overlooked something please let me know.

The only practical issue is what should happen on an unforced king sacrifice: does the player lose through having made an illegal move, or should he take the move back and play another?

I'm not seeing anything Abbott has said that outlines special considerations for someone ending their turn with their king in an attacked position. If there are no rules addressing it, then presumably it would need to be resolved either by the rules or by the players making something up themselves. If it's determined by the rules, the only rule that seems related at all to this scneario is the first one: you are allowed to capture the enemy king.

Looking at Shogi, the 将棋連合規定 offers a similar resolution: If a player's move leaves their own king in check, and their opponent points it out, the player immediately loses the game. The outcome of this scenario is mechanically equivalent to the opponent noticing the king is being attacked and capturing it.

Then again, on the chessvariants page for Shogi, I don't see any mention of how these types of situations are resolved. Presumably it is left as an exercise for the players to decide how they'd like to resolve a rules breach when it arises. Perhaps that could be assumed here as well.

All I know is that throughout his entire life, Abbott has been very consistent with his choice of wording for what "the object of the game" is in Ultima, and yet in our "object of the game" section we aren't respecting that wording. We're actually saying the exact opposite.

When a game's creator states "the object of the game is to capture the king" multiple times, and eventually elaborates to specifically say "the object of the game is to capture the king, not achieve checkmate," it seems inappropriate to write that the object of the game is to "achieve checkmate."

I'd hope we could just write what the creator said, instead of the exact opposite of what he said. His own words aren't going to misrepresent him.

in Chess the object is to capture the king, not achieve checkmate.

No one says that of orthodox Chess, because it obviously would not be true there: there is no way to win an orthodox Chess game other than by checkmating the opponent. Not so in Ultima, where stalemate is a second winning condition, rather than a draw. And 'smothered stalemates', where a player doesn't have any moves even when he would be allowed to expose his king, are not nearly as hypothetical in Ultima as in orthodox Chess: Pieces without replacement capture can easily be boxed in, even if they are not frozen by an Immobilizer. So I would not exclude that the sentence was just intended to convey that stalemating is an alternative.

From a game-theoretical perspective there is no ambiguity in the rules: checkmate and stalemate are both won positions, whether the game ends there or whether one in some cases would have to play one more move to actually capture the king. So the whole discussion is about what I would call "game etiquette": what is the proper procedure for claiming the victory when the opponent exposes his king to capture. Should you actually capture the King and press the clock, or should you just stop the clocks and submit the claim? Or is this not a victory at all if there was an alternative, and should you allow the takeback and that alternative to be played, possibly in combination with a time penalty?

Some of the quotations attributed to Abbott seem to contradict each other, though. There can be two reasons for that: he actually changed his mind at some point how the game should be played, or he has always thought the same about that, but failed to express himself unambiguously. In the latter case we could speculate on what he actually meant. If it is correct that Abbott at any time mentioned that it was not allowed to expose your own king to check, this strongly suggests that he thought a move that did should be handled as per FIDE rules: take back and play another one. For if it would be handled the Shogi way (instant loss), there wouldn't be much reason to mention it at all: the game is over anyway, either by claim or by king capture, unless the players don't notice it, in which case it doesn't matter what the rule is, as it isn't going to be invoked. So it is a matter of weighing the "not by checkmate" against "it is illegal to put your own king in check", I would say the latter of those is the least likely to have meant anything else as what it says.

I can add that no matter what Abbott actually meant, tournament organizers are likely to enforce their own game etiquette. E.g. an on-line interface would be likely to make it impossible to enter moves that expose the king to begin with, and perhaps automatically resign for a player that is checkmated.

From a game-theoretical perspective there is no ambiguity in the rules: checkmate and stalemate are both won positions, whether the game ends there or whether one in some cases would have to play one more move to actually capture the king.

This isn't correct because players aren't perfect agents. They do not always identify and make the most optimal move. It is possible that someone in "checkmate" will move their king into an easily missed "check" (e.g. a check from the coordinator), and the opponent won't realize they could still capture the king.

Whether this is allowed or not clearly makes a difference when played in any setting with a third-party overseer (an arbiter, a computer client, etc).

he actually changed his mind at some point how the game should be played

Well, we know this is the case to some degree because the 1968 rules are very different from the 1963 rules. He then decided those had been a bad idea, and went back to the 1963 rules.

He even stated in both 1962 and 1963 that the game was still freshly developed and may still have issues. It isn't that surprising for some language of a newly designed game to be contradictory; an aspect of the game started out one way, and later in the design process was changed, but the rest of the rules weren't updated accordingly to reflect the change.

It should be assumed the part of the contradiction that was intended was the part the creator later explained was intended (capturing the king), especially when he also said the other part of the contradiction was not intended (the checkmate).

E.g. an on-line interface would be likely to make it impossible to enter moves that expose the king to begin with, and perhaps automatically resign for a player that is checkmated.

This reminded me that Abbott promoted "Zillions of Games" as a software that accurately enforces the rules of Ultima.

I just found and installed this piece of software and tried a game of Ultima on it. You can play against the computer or against other people.

In this interface that Abbott promoted as correct, you are allowed to enter moves that expose the king. You are allowed to move your king from a safe position into an attacked position. It does not automatically resign, allowing the opponent to make a mistake and miss a capture. You must capture the king to end the game, whereupon it says "King captured. Black wins!"

what is the proper procedure for claiming the victory when the opponent exposes his king to capture

According to the software Abbott promoted, the proper procedure is to capture the king.

I would not exclude that the sentence was just intended to convey that stalemating is an alternative.

No. As someone who loves Robert Abbott's work, I'm not okay with this blatant misrepresentation of his words. His paragraph again was:

The first puzzle is Mate in 1 and all the others are Mate in 2. This follows the conventions of chess problems, even though in Ultima the object is to capture the king, not achieve check mate. So, Mate in 1 should be translated to Capture the king in 2 moves (that is: White moves, Black moves, then White moves and captures the king). Mate in 2 translates to Capture the king in 3 moves.

After saying "in Ultima the object is to capture the king, not achieve check mate," he elaborated with "So" and even explained what he meant with "(that is: White moves, Black moves, then White moves and captures the king)." There is no way to misunderstand this language, and the attempt to do so makes me question the motivation behind it.

And again, these puzzles which require the king to be manually captured per the rules of Ultima were made in 1964, and explained in 2004. It makes it very clear what Abbott's intention was, and the only interface Abbott promoted for playing Ultima works that way as well.

Well, if Abbott expressed his ideas as a computer program, it doesn't matter what he said elsewhere at all. There is no ambiguity in computer code.

Since today is the last day of my paid subscription to Leonardo.Ai, I have been generating lots of images. Here are some I generated for Ultima pieces using only the name used in Ultima. I will display them without names, though you could find out what they are by examining the URL. Without doing that, what do you think each piece is? Were you able to recognize all the pieces? How suitable do you think pieces like these would be?