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I made a few more edits. You use the word field a lot to refer to spaces. Is Feld the word for space in German?

While the concept behind this game seems interesting, I am not clear on the mechanics of movement. In your Knight diagram, it does not look like you have applied the rule for the Knight's movement consistently. The Knight on 5 is shown being able to move to g7, but 5 and g7 are on the same diagonal.

It is not clear to me what this diagram is illustrating:

I use the word 'field' as a synonym for playing field or square. 'Field' has nothing to do with space in German.

Fig.10: The diagonal from 5 affects the squares up to e8 or up to d1, so g7 is not on the same diagonal. The rules are therefore applied consistently.

The diagram should clarify the following: A move between field 4 and field a4 respectively a move between field 5 and field h5 isn't possible. In the row the next field which can be reached by 4 is field b4 (g5 by 5).

I'm still not following how Bishop or Knight moves work. I think more procedural descriptions of how these pieces move would help.

In this diagram, it looks like the Bishop can move from b5 to b3 or from g4 to g6. Is that a correct interpretation? Step-by-step, how is the presence of transfer fields affecting the Bishop's moves?

Step by step: The bishop can change his diagonal. That's the point of this variant. From b5 to b3 or from g4 to g6 (and so on up/down the diagonal) means that the bishop has changed his diagonal.

When you said step by step, I was expecting a step by step explanation, but you didn't provide one. Could a Bishop move from d1 to e8 along the path d1-c2-b3-a4/4-b5-c6-d7-e8?

I use the word 'field' as a synonym for playing field or square. 'Field' has nothing to do with space in German.

The English word ‘space’ is used to refer to individual squares (or other shapes if boards are irregular) of the board. ‘Square’ is also used, as is ‘cell’ (especially in 3D) or ‘hex’ in hexagonal‐cell games. As ‘Feld’ is indeed, as Fergus rightly intuited, used for the same thing in German, it is thus the German word for space in this sense. Conversely, ‘field’ in English is rather unusual as a way of referring to spaces (i.e. squares ⁊c.)

Of course the usual sense of ‘space’ is better translated as ‘Raum’ or the like (hence e.g. Raumschach), but that sense is not what's meant here

This reads better, but it seems to be stating the obvious

My reading of the German suggests that ‘Farbtransfer’ — i.e. ‘Colour Transfer’ — is being use in a slightly more technical sense to refer to a particular kind of event (cf. e.g. ‘Bishop Conversion’ due to Carlos Cetina, which is more specific than simply converting bishops by some arbitrary means); after all, neither ‘Farbtransfer’ nor ‘colour transfer’ is an everyday word or phrase. And since the German also does not mention possibility (*‘dann muss ein Farbtransfer stattfinden können’) I'd probably translate it as your tautological‐looking one, but with ‘Colour Transfer’ capitalised

Could a Bishop move from d1 to e8 along the path d1-c2-d4/4-b5-c6-d7-e8?

Assuming ‘d4’ is a typo for ‘a4’, then my reading of the rules agrees that it could indeed take this path, or instead a path d1–e2–f3–g4–5–g6–f7–e8.

The position on the Switches must be clear. Either field 4 or field a4 [but not both; analogously for 5/h5] must be occupied

In other words, a piece moving onto the switch must choose on the turn that it gets there which squares it can move off onto? And so e.g. a rook can checkmate a king on h8 from h1, h2, h3, or h4, but not h5 or 5?

Assuming ‘d4’ is a typo for ‘a4’,

Yes, and I made some other typos, which I have since corrected in the original.

"Could a Bishop move from d1 to e8 along the path d1-c2-b3-a4/4-b5-c6-d7-e8?" (a4/4 is a typo, h5/5 is correct)

Yes, that is possible, but only in two moves. The first move goes up to square 5 and in another move up to e8. It's like normal chess. The bishop started from a white diagonal and after a second move the bishop stands on a 'black' diagonal. This means a color transfer (Color Change or whatever is correct) has taken place.

"Assuming ‘d4’ is a typo for ‘a4’, then my reading of the rules agrees that it could indeed take this path, or instead a path d1–e2–f3–g4–5–g6–f7–e8."

The path d1–e2–f3–g4–5–g6–f7–e8 is absolutely correct - but in two moves. Move 1 via d1-e2-f3-g4 to square 5, then move 2 via g6-f7 to square e8.

"And so e.g. a rook can checkmate a king on h8 from h1, h2, h3, or h4, but not h5 or 5?"

That's not according to the rules. Correct is: a rook can checkmate a king on h1 from h8, h7, h6, but not from h5 or 5.

The parallel situation looks like this: a rook can checkmate a king on a8 from a1, a2, a3, but not from 4 or a4.

That's not according to the rules. Correct is: a rook can checkmate a king on h1 from h8, h7, h6, but not from h5 or 5.

Of course. I think I accidentally started on the wrong side of the board and then applied half a correction (it was late last night). But in any case that still answers my question, Thanks

"Could a Bishop move from d1 to e8 along the path d1-c2-b3-a4/4-b5-c6-d7-e8?" (a4/4 is a typo, h5/5 is correct)

No, a4/4 is not a typo. It is sandwiched between b3 and b5, and h5/5 is on the other side of the board from these spaces.

Yes, that is possible, but only in two moves.

Okay, but here's what you wrote previously:

"In this diagram, it looks like the Bishop can move from b5 to b3 or from g4 to g6. Is that a correct interpretation?" Yes, that is the correct interpretation.

To be clear, my questions were about what a Bishop could do on a single move. If the longer move I described cannot be done as a single move, then I would presume that B b5-b3 is illegal for similar reasons. Or is there some asymmetry that allows one and forbids the other? I should ask, could either "B b4-b3" or "B b3-b5" ever count as a legal move?

I have indeed trouble with your question. I don't understand how "B b4-b3" or "B b3-b5" has anything to do with a bishop's moves.

I want to answer your question like this and hope that I'm on the right track. You ask what a bishop can do with one move.

Let's start from d1. The bishop can move to the left via c2-b3-a4 to square a5. The following move is also possible: d1 via c2-b3 to square 4. From there, the color change takes place in a second move by reaching the squares b5-c6-d7 to e8. To the right, the bishop can go to square 5, via e2-f3-g4.

If you think that's an asymmetry, then that's the result of the new board geometry. The opponent has the mirrored move options and thus equal opportunities.

Did I understand and answer your question correctly?

I have indeed trouble with your question. I don't understand how "B b4-b3" or "B b3-b5" has anything to do with a bishop's moves.

You may be familiar with abbreviated algebraic notation, such as Bb3, which would mean to move a Bishop to b3. This abbreviated notation depends upon knowledge of the position and knowledge of the rules. Without these, you don't know where the Bishop is, and if a player has more than one Bishop, you don't know which Bishop to move there.

Since Chess variants are played by a variety of different rules, it helps to use a generic rule-blind notation that can work equally well for different variants. The notation I used explicitly spells out a move in a manner that someone could follow without knowing the rules of the game in question. First of all, "B b4-b3" is a typo. I meant to write "B b5-b3", which means a move by the Bishop on b5 to b3. This is a possible move only if there is already a Bishop on b5, and whether it's a legal move depends on the rules of the game. In Miller's Spherical Chess, for example, it would sometimes be a legal move. Likewise, "B b3-b5" means a move by a Bishop on b3 to b5. It should now be evident what these have to do with Bishop moves.

Thanks for your explanations, I didn't know that. This abbreviated notation makes sense.

The moves "B b5-b3" and "B b3-b5" you mentioned as examples are not legal moves in my variant. With the exception of the rules for the new squares 4 and 5 and for the switches 4/a4 and h5/5, the FIDE rules are valid exclusively.

I think we've clarified that a Bishop cannot pass through a transfer field on its move. To switch color, it must stop on a transfer field, and then it may use its next move to switch to spaces of the other color.

My next question concerns which directions of movement are available to a Bishop on a transfer field. Let's say a Bishop is on a4/4. I presume it can move to a5, b5, c5, or c3, but it cannot move to a3. Likewise, a Bishop on h5/5 could move to h4, g4, f4, and g6 but not to h6. Is that correct?

The way I understand it is that ranks 5-8 are shifted one square left:

Whenever a move passes through a4 from below, it can be continued normally, or like the upper board half was not shifted (i.e. from a4'), and similar for h4 reached from above. a4' cannot be reached from below.

"Let's say a bishop is on a4/4."

Let me be specific: a bishop doesn't stand on a4/4; he stands either on 4 or a4. The player must clearly mark the location.

If the bishop is on 4, then his path goes via b5, c6, d7 to e8. In the other direction it goes via b3, c2 to d1.

If the bishop is on a4, then he can choose; he can go down to d1 as before. He can move upwards to a5 in a first move, to go via b6, c7 to d8 in a second move. The other option is to move to f8 via c5, d6, e7.

There are no other move-options.

"Whenever a move passes through a4 from below, it can be continued normally, or like the upper board half was not shifted."

That is correct!

"a4' cannot be reached from below."

Of course, a4' (I'll call it 4) can be reached from below. For example, if you start from d1, you can reach the switch 4/a4 upwards. The player must then decide whether to occupy square 4 or square a4 and mark this clearly through his positioning. After that he either stands on 4 or on a4. Then the player can proceed as described in the reply to Fergus Duniho.

What I meant is that a4' cannot be reached from a3.

My description was not complete, though, as I did not mention what would happen when a move starts from or ends on a4/a4'. I understand now that when you end there you have to choose which of the two to occupy. Which is only relevant for when you move into the upper board half; a move into the lower board half would always look as if you started from a4.

Can a Rook move through a switch on a single move? Which of these moves could be legal?

• R a1-a8
• R a1-b8
• R a8-a1
• R b8-a1

"Can a Rook move through a switch on a single move?" Yes, of course. Otherwise, a rook on a1 could not checkmate a king on a8 in one move.

R a1-a8 = legal; R a1-b8 = legal; R a8-a1 = legal; R b8-a1 = legal

"What I meant is that a4' cannot be reached from a3."

Why not? A rook, pawn or queen starting from a3 and occupying the switch must decide which square of the switch is to occupy - 4 or a4.

"a move into the lower board half would always look as if you started from a4."

That's not true: A rook on a8 that wants to move to the lower half of the board can occupy square 4, but not a4. A rook on b8 can occupy a4, but not 4. Incidentally, in this direction the distinction between 4/a4 makes no sense for a rook (or queen). The switch only works in one direction. Either from the lower half of the board starting from a1, a2, a3, or from the upper half of the board starting from h8, h7, h6.

By a Bishop. In the way I had drawn it, the orthogonal moves you describe would not enter a4' directly; they would enter a4, and then optionally transfer to a4'.

The other phrase you quote was intended to describe what happens when you start on a4/a4'.

It is still a bit ambiguous how a knight could move from h6 if h5/h5' is occupied, (and the switch thus in a known position).

May I refer to an earlier answer, which I hope answers your question:

"Let's say a bishop is on a4/4."

Let me be specific: a bishop doesn't stand on a4/4; he stands either on 4 or a4. The player must clearly mark the location.

If the bishop is on 4, then his path goes via b5, c6, d7 to e8. In the other direction it goes via b3, c2 to d1.

If the bishop is on a4, then he can choose; he can go down to d1 as before. He can move upwards to a5 in a first move, to go via b6, c7 to d8 in a second move. The other option is to move to f8 via c5, d6, e7.

There are no other move-options.

Right. So there is no path 4-a3-b2-c1. Which is what I meant, and needed to be said, because in the representation I had drawn, it looked like there could be.

I am still looking for a somewhat more intuitive description. It looks like 4 and a4 are really the same cell, (double width in my drawing), which always borders b4. And that there is a sliding door that either closes off the connection with a5 or b5, which has to be set as soon as you enter 4/a4, and can then not be altered until you leave it. (Which could be on the same turn.) Entering from above forces you to set the door such that you could enter.

Something doesn't work with this diagram. Maybe it is because only 2 colors are used, and a third one, neutral, should be used. Or because the triangular/losange doesn't work fine and something else has to be imagined.

I see the comments. It needs a lot of imagination to visualise something else and tell our brain that what we see is not right. What I see is simply a 66-cell board, where c1-b2-a3-4 is a diagonal, as well as 4-b5-c6-d7-e8, both being dark.

And a8-a7-a6-a5-4 is a column simply ending in 4. Like h1-h2-h3-h4-5, ending in 5.

That board only shifts the column (a to b, b to c, etc.) at the middle line. It doesn't change the color of the diagonals at all.

I understand the idea behind, but I think it needs to be worked more.

A somewhat simplified version of the same idea is this:

There is only a single, double-width cell a4 here, and there is no additional game state to distinguish between an occupant being in the right or left half of it. Moves (or move continuations) that leave a4 to 5th rank can choose whether they consider a5 or b5 the only square that connects to the upper edge of a4. So a4 has 2 'north' exits (to a5 and b5), two 'north-east' exits (to b5 and c5), and a single 'north-west' exit (to a5).

The difference with the rules that were given is that 'forward' moves even fork from a4, in addition to a1-a3.

How a Knight should move in the vicinity of the switch fields depends on which of the (normally equivalent) descriptions of Knight moves one adopts for the regular part of the board. The description "all two-step King moves that cannot be made by a Queen" is a rather unusual one; commonly one finds "one orthogonal King step followed by an outward diagonal one" (i.e. a non-lame Mao) or L-shaped "2 orthogonal steps plus a perpendicular one". Where the latter might also allow the move to start with the short leg. In my opinion the non-lame Mao description would be most intuitive here.

If I may summarize from my point of view:

I gather from the comments that my version is not easy to understand. But that's not a disadvantage a priori. It remains to be seen whether the possibility of checkmating the king with just one piece will play a role in chess. The same applies to the bishop, who can now change his color diagonal.

But if I see it correctly, then there are no bugs in the variant and the set of rules is consistent. Complicated, yes, but conclusive.

I gather from the comments that my version is not easy to understand.

I don't know if it's that or if you just haven't explained it clearly.

But if I see it correctly, then there are no bugs in the variant and the set of rules is consistent.

With respect to the Bishop, you told me that it can occupy only 4 or a4 or only 5 or h5. I presume the same holds for other pieces. So, a Rook on one of these spaces would not command two files. Likewise, a Knight on one of these spaces could not move as though it were on the other space. However, that looks like what the Knight is doing in your example. It's on 5, and its ability to move to f4 or g3 makes sense in light of that. But its ability to move to e4, f6 and g7 would make sense only if it were on h5 instead of 5.

I agree with your understanding Fergus. The best way to describe this geometry in a consistent manner for all pieces, remains to consider a4 and 4 (or h5 and 5) as a double cell. A piece on this double cell can be seen as being on both. Then, the diagram drawn by H.G. is fully correct.

a Knight on one of these spaces could not move as though it were on the other space. However, that looks like what the Knight is doing in your example

That much is clarified in the accompanying text. All three of e4, f6, and g7 can be reached by an orthogonal step (taking into account the rule about sideways moves from 5 going directly to g5) followed by a diagonal step.

This holds equally well whether we use the author's preferred definition for the knight move or either of the more common ones H.G. suggested

there are no bugs in the variant and the set of rules is consistent. Complicated, yes, but conclusive.

Afaict, the rules themselves are indeed consistent (and may well lead to an interesting game), but the explanation could be clearer, as shown by the fact that they seem to be unclear in some respect of another to most of the readers here.

Also I second H.G.'s request for clarification on the matter of knights moving through/over closed switches

I have begun to program Chess66 for Game Courier. So that 4 and 5 have separate file labels, I'm calling them A4 and H5 and distinguishing them from a5 and h5. I'm programming it with logical directions, which lets me define named directions as linked lists of nodes. The way directions are defined, the same direction cannot have two destinations from the same space. This means I've had to define additional directions to handle some lines of movement. However, the same direction can go from different spaces to the same destination.

One of the main difficulties I'm coming across is that sometimes it makes sense to treat A4 and a4 or H5 and h5 as separate spaces, and sometimes it makes sense to treat them as the same space. One idea would be to put an invisible dummy piece on the unoccupied space when the other one is occupied. That way, movement through a switch would be completely blocked.

At present, more work needs to be done to get the directions working properly.

Since a Bishop that moves to 4 could immediately switch to a4, is the reverse also true? Could a Bishop moving to a4 immediately switch to 4? More generally, is switching between these spaces available for any piece or only for Bishops?

The separation of the squares 4/a4 and h5/5 in the switches applies to all game pieces, including pawns.

Maybe I can clarify again from my point of view, especially for the knight:

A choice between the squares 4/a4 and h5/5 only goes in one direction. If a piece starts from a1/a2/a3 or from d1, c2 and so on, then there is a choice between squares 4 and a4, whereby the positioning must be clearly on 4 or a4. This means that the choice in a switch is only possible from 'below'. A rook/queen on the rank 4 can only occupy square a4 and not square 4. This applies to the switch h5/5 vice versa.

To clarify with the knight: A knight on 5 can move as shown in figure 10. Knights on g7 or f6 can occupy 5 or h5 because they come from 'below'. A knight on e4 can only reach h5 and not 5. A knight on g3 can only reach 5 but not h5. And a knight on f4 can move to 5 but not to h5.

This means that the squares of a switch are always seen separately and not partially as a same space.

It might be a bit difficult, but I hope it's consistent.

By what series of moves can a Bishop change to spaces of the other color?

Let me emphasize again: A change between 4 on a4 or h5 and 5 is not possible.

Some examples.

Bischoff on d1 to the left:

Standing on a4 after the move, a color transfer is not possible. Standing on 4 after the move, then a color transfer is possible. Because from there you can continue in the next move via b5, c6 etc., a color change has taken place.

Bishop on d1 to the right:

The move can go up to 5 (and not h5, this square cannot be occupied). The next move can be continued via g6, f7 etc. There has also been a color change.

For the other half of the board everything is vice versa.

Does that answer your question?

The more it's explained, the less I understand. The "a bit difficult" seems soft in my case. Here,

"Bishop on d1 to the right: The move can go up to 5 (and not h5, this square cannot be occupied). The next move can be continued via g6, f7 etc"

How come the Bishop goes from 5 to g6?

You said h5 cannot be occupied (by this Bishop I presume).

When the Bishop goes from 5 to g6, is it affected if another piece stands on h5?

Does that answer your question?

No, it does not. I specifically asked for a series of moves, and I didn't get that. What will answer my question is a series of moves in the generic rule-blind style of notation I used earlier. You do not have to write anything in English to answer this question.

a series of moves in the generic rule-blind style of notation I used earlier

The move sequences given by Gerd in his comment are B d1–4; B 4–b5 and B d1–5; B 5–g6. He also notes that B d1–h5 is not legal, but B d1–a4 is.

How come the Bishop goes from 5 to g6?

The top corners and the top and left sides are shared between h5 and 5, but the bottom side and corners are different. So 5 behaves as h5 from above (and cannot be occupied at the same time as it), and so is diagonally adjacent to g6.

When the Bishop goes from 5 to g6, is it affected if another piece stands on h5?

5 and h5 cannot be occupied simultaneously, so this situation does not arise. But since both are diagonally adjacent (by the same corner) to g6, it would presumably be fine if they could.

The move sequences given by Gerd in his comment are B d1–4; B 4–b5 and B d1–5; B 5–g6.

So, I gather that the following are all legal moves:

• B d1-4
• B 4-d1
• B e8-5
• B 5-e8

I think I misread an earlier answer. This actually describes one move on black spaces and the other move on white spaces:

If the bishop is on 4, then his path goes via b5, c6, d7 to e8. In the other direction it goes via b3, c2 to d1.

So, it looks like the diagonal from 4 to the first rank is a different color than 4, and the diagonal that goes from 5 to the last rank is a different color than 5, and that is how the color changing is done.

Suppose I have a Rook on d4. Could it move to 4? Or could it only move as far as a4? Likewise, could a Rook on d5 move to 5, or could it only move as far as g5?

I had already answered that before, as follows:

A rook/queen on the rank 4 can only occupy square a4 and not square 4. This applies to the switch h5/5 vice versa.

"So, I gather that the following are all legal moves:

B d1-4, B 4-d1, B e8-5, B 5-e8"

That is absolutely correct.

"So, it looks like the diagonal from 4 to the first rank is a different color than 4, and the diagonal that goes from 5 to the last rank is a different color than 5, and that is how the color changing is done."

By the way: The squares 4 and 5 do not have a uniform color. The squares are each composed of both colors. This is the only way to make a color change possible.

I try to follow. So a Rook cannot go from a4 to 4. And I understood that if there is a piece on a4, it is not possible to have another piece on 4.

At the end I wonder if this game is simply playable. I wouldn't be able to explain it to anyone I'm afraid.

I'm pretty sure that it would be possible to build something interesting on Gernd's idea by melting the cells a4 & 4, as well as h5 & 5. Which was similar to HG's diagram.

Doing this

• only 1 piece allowed on a4/4 or on h5/5
• a Rook on a1 would threat up to b8 AND a8 (as wished by Gernd)
• a Rook on h4 would threat up to a4/4
• a Bishop on d1 would go up to a4/4
• a Bishop on a4/4 would either go to f8 (keeping the color) or to d8 (switching the color).
• a Knight on a4/4 could go to b6, c5, a6, c6, b3, a2, b2, c3 (interesting)
• Chess 66 would have 64 cells which is maybe the real problem.

Dear En Bw, thank you for your comment, which is absolutely correct.

I'm testing my code for Chess66 on Game Courier right now, and with a Knight on a3, I currently have its legal moves as a5, c5, c4, c2, and b1. Because 4 is right above it, it looks like b5 could be another legal move by going over 4 and a5 and turning right to b5. It could be argued that this is illegal because there is a single-direction path from a3 to b5. But if that rules that out, it might also rule out a5 as a legal move, because there is a single-direction path to it through 4.

I don't think that the moves to a5 and b5 are legal since they are on the same line. Merging the squares 4 and a4 would not change that. On the contrary, the possibility of being able to detect movements on the same line or the same diagonal would be diluted.

A rook/queen on the rank 4 can only occupy square a4 and not square 4. This applies to the switch h5/5 vice versa.

That's interesting; given that a rook is allowed to move sideways from 4 onto b4 and beyond, that means that a rook on 4 can threaten a rook on b4 without being attacked back. Is this intentional?

The squares 4 and 5 do not have a uniform color. The squares are each composed of both colors.

Strictly speaking, the colours on the squares are a representational convention and bear no real influence on the game; ‘a bishop can change colour’ is equivalent to saying a bishop can reach the whole board, or in other words all squares are effectively the same colour. But that's a minor quibble

En Bw

I assume you mean me? That's one correct letter out of four, with two more misplaced ;)

I don't think that the moves to a5 and b5 are legal since they are on the same line.

That's one of the few things which changes depending on the knight‐move definition; the definition you've chosen would indeed exclude both destinations, as a queen can reach both of those squares; but the more usual definitions H.G. first brought up (either two othrogonal steps in one direction and one at right angles, or (my preferred expression) one orthogonal and one diagonally outwards — in either order (or not…?) and for some suitable definition of ‘outwards’) would probably allow both moves. Equally the question of whether N h4–g6 is legal, and probably other similar moves, is implicated there. There may be some way of defining the knight move to include only a subset of the moves in question, but that's unltimately for Gerd to decide if he wants to look for (or someone else to contribute if they come up w/ sth).

En Bw

I assume you mean me? That's one correct letter out of four, with two more misplaced ;)

The other one was turned upside-down but left in place. So, they're all there with some mix-ups. :)

I'm done working on Chess66 for Game Courier today. The directions are looking good, but I still have to adapt the Pawns to work with switches, and I still have to prevent double occupancy of the switches. Since Firefox won't remember this after I shut down my computer, here are the moves I've been making to test things out. In the meantime, feel free to check it out, and apart from the issues I just mentioned I still need to work on, let me know if you find any illegal moves it permits or any legal moves it doesn't permit.

1. P c2-c4 
1... p f7-f5 
2. Q d1-A4 
2... q e8-H5 
3. Q A4-a7 
3... p f5-e4 
4. N b1-a3 
4... q H5-e5 
5. P c4-d5 
5... q e5-d4 
6. N a3-c5 
6... p e7-e6 
7. Q a7-a3 
7... b f8-e7 
8. N c5-A4 
8... b e7-g4 
9. P b2-b3 
9... b g4-H5 
10. P b3-b4 
10... q d4-b4 
11. Q a3-g3 
11... p g7-g5 
12. P d5-e6 
12... p g5-f4 
13. Q g3-h7 
13... r h8-h7 
14. N A4-d5 
14... b H5-g6 
15. N g1-h3 
15... n b8-c6 
16. N d5-a4 
16... b g6-h5 
17. N a4-c3 
17... q b4-c5 
18. P e2-e3 
18... b h5-h4 
19. P a2-a3 
19... q c5-h5 
20. N c3-a4 
20... q h5-h6 
21. N a4-c6 // - Check! -
21... p b7-c6 
22. N h3-f4 
22... q h6-e6 
23. N f4-h6 
23... q e6-d5 
24. N h6-f5 
24... n g8-h6 
25. N f5-c4 
25... b h4-e8 
26. P a3-a4

8. N c5-A4

According to my definition, the switch can only be operated from 'below'. After that, the move N c5-A4 would not be possible. N d5-a4 would be possible. However, in my reply to Bn Em I proposed an extension of my definition.

17. N a4-c3 ---> N a4-c2

18. N f5-c4 ---> N f5-d4

"En Bw" - sorry, won't happen again.

"That's interesting; given that a rook is allowed to move sideways from 4 onto b4 and beyond, that means that a rook on 4 can threaten a rook on b4 without being attacked back. Is this intentional?"

That doesn't seem logical indeed.

Assuming a rook is on 4 and an opponent's rook is on e4, my definition means that the rook on 4 can attack the rook on e4, but the reverse is not possible. That's inconsistent. It is probably appropriate to add that the switch can be operated not only from 'below' but also from the side. This would eliminate the inconsistency.

It is probably appropriate to add that the switch can be operated not only from 'below' but also from the side.

Seeing as it can also be operated from ‘above’ too, if not already occupied (i.e. from my understanding, B a4–c2; R a6–4 is legal), I would agree that'd make sense.

17. N a4-c3 ---> N a4-c2

25. N f5-c4 ---> N f5-d4

?? Are those corrections? Aren't those diagonal moves, the way you've assigned file labels? of two and one steps respectively?

According to my definition, the switch can only be operated from 'below'. After that, the move N c5-A4 would not be possible.

A switch is an overlapping pair of spaces that in some ways operate together as a single space. By their very nature, they operate as a switch only from a given direction. From below, a piece is given two choices for how to continue its vertical movement. However, this property of a switch is not a property of the individual spaces whose overlap constitutes the switch. So, restrictions on movement to A4 have nothing to do with your definition of a switch. They are simply arbitrary restrictions on movement.

There are already other examples of A4 being reachable from above. For example, a Rook or Queen on a8 could move to A4, and a Bishop or Queen on e8 could move diagonally to A4. You have also agreed that it makes sense to let it be reachable from the side.

I'm now going to propose some rule changes. Since the switch can make a piece more powerful, this should be balanced by making a piece using a switch more vulnerable. Allow pieces access to the spaces of a switch from any direction, and when a piece moves to a switch, allow capture of any piece on the switch even if the capturing piece moves to the other space. For example, if a Bishop is on A4, and a Rook moves to a4, consider the Bishop on A4 to be captured.

Currently, the Knight is the only piece whose powers of movement are restricted in the vicinity of a switch. Correct this by allowing a Knight to move to any space that can be reached by a step in an orthogonal direction followed by a step in an outward diagonal direction, or by a step in a diagonal direction followed by a step in an outward orthogonal direction. This is the normal definition for how a Knight moves in Chess and other variants, and it would allow the Knight to also increase its capabilities in the vicinity of a switch.

One last rule change I would suggest is to let Rooks, Queens, and Kings use their ability to move horizontally to switch between the spaces constituting the switch. This would basically involve lifting one more restriction on movement to the spaces making up a switch.

The moves B a4–c2; R a6–4 are legal moves, they are conform to the rules.

Move 17: N a4-c3 doesn't seem legal, but N a4-c2 would be legal.

Move 25: N f5-c4 doesn't seem legal in same way, but N f5-d4 would be legal again.

I have started writing up a brief summary of the rules to appear underneath the board for Game Courier.

Move 17: N a4-c3 doesn't seem legal, but N a4-c2 would be legal.

It looks legal to me. Why wouldn't this move be legal? Meanwhile, a4 and c2 are along a diagonal, and N a4-c2 would definitely be illegal.

Move 25: N f5-c4 doesn't seem legal in same way, but N f5-d4 would be legal again.

N f5-c4 is a perfectly legal Knight move, and I see no reason why it would be illegal. Meanwhile, f5 and d4 are diagonally adjacent, and N f5-d4 is clearly illegal.

When you're examining the moves, be sure to click on Record, paste the moves into the box, and click on View. This will let you view each position. I think you made some wrong judgements, because you got confused about how notation for this game works. Vertical movement shifts to an adjacent file as it goes between the 4th and 5th ranks. So, the space immediately above d4 is e4, for example.

You can agree on almost everything, certainly to make the game playable and programmable. Regardless of that, I can only say my point of view and describe my intentions.

"A switch is an overlapping pair of spaces that in some ways operate together as a single space."

From my point of view it looks different. The square a4 of a switch is an independent square and is completely identical to the square a4 in normal chess. 4 (A4) is a composite square consisting of a half and triangle part of a4 and the new triangle due to board geometry. The new square 4 (A4) gets the same play options as all squares of the game board - 4 (A4) is considered equal.

This means that the squares a4/4 (A4) must first be seen independently. These independent fields get an additional function when they work together and act as a switch, as described.

My intention is therefore not compatible with the proposal to merge fields 4/a4 (A4) as proposed by Jean-Louis.

It is possible to agree on the sides from which the switch should be accessible. We have clarified access from below and from the side, access from above is also not a problem and is already part of my proposal. The only question is whether it is access to the switch as a unit or to the individual square of a switch. According to my intention, the second applies.

"Allow pieces access to the spaces of a switch from any direction, and when a piece moves to a switch, allow capture of any piece on the switch even if the capturing piece moves to the other space. For example, if a bishop is on A4, and a Rook moves to a4, consider the Bishop on A4 to be captured."

As described, access to the switch from all sides is not a problem. It is possible to agree on the proposal, but it does not fit my intention. However, if the game becomes more playable and programmable - so what.

To the Knight: I can't allow anything here, but I can say what my point of view is. If we stick to the fact that the squares of a switch should be seen separately, then knight moves ending on the same line are not possible. However, as the game becomes more playable and programmable, compromises should be possible.

"One last rule change I would suggest is to let Rooks, Queens, and Kings use their ability to move horizontally to switch between the spaces constituting the switch. This would basically involve lifting one more restriction on movement to the spaces making up a switch. "

I have problems with that. I have emphasized that the squares of a switch represent independent squares. This would rather mean that moves between the squares of a switch are possible. The independence of the squares on the one hand and the functionality of a switch on the other compete with each other. Regarding the direct change between the squares of a switch, I tend towards the superordinate function, so a direct change should not be possible. At least that's my intention. But here, too, compromises determine reality.

You're right. I have disregarded the change between the 4th and 5th rank. I fell into my own trap :).

"A switch is an overlapping pair of spaces that in some ways operate together as a single space."

From my point of view it looks different. The square a4 of a switch is an independent square and is completely identical to the square a4 in normal chess. 4 (A4) is a composite square consisting of a half and triangle part of a4 and the new triangle due to board geometry. The new square 4 (A4) gets the same play options as all squares of the game board - 4 (A4) is considered equal.

This means that the squares a4/4 (A4) must first be seen independently. These independent fields get an additional function when they work together and act as a switch, as described.

I didn't say anything different. We're in agreement that the spaces composing a switch are separate from each other. But since they cannot be simultaneously occupied, and occupation of one space blocks movement through the other, and they share a common edge and a common corner, they also function in some ways like the same space.

It is possible to agree on the sides from which the switch should be accessible. We have clarified access from below and from the side, access from above is also not a problem and is already part of my proposal. The only question is whether it is access to the switch as a unit or to the individual square of a switch. According to my intention, the second applies.

Agreed. Use of the switch as a switch is possible only from below. That is due to the nature of how it works. If a piece moves to a switch through a diagonal move or a Knight move, it will have to stop on the switch, which will prevent it from using the switch to alter the direction of its movement. The same is true if a Rook or Queen moves to a switch from the side. It will have to stop there, which will prevent its use as a switch. And if a Rook or Queen moves to a switch from above, it will have only one path through the switch. So, it won't be utilizing the switch as a switch. This shows that access to the spaces composing a switch is a completely different matter than using it as a switch.

"Allow pieces access to the spaces of a switch from any direction, and when a piece moves to a switch, allow capture of any piece on the switch even if the capturing piece moves to the other space. For example, if a bishop is on A4, and a Rook moves to a4, consider the Bishop on A4 to be captured."

As described, access to the switch from all sides is not a problem. It is possible to agree on the proposal, but it does not fit my intention. However, if the game becomes more playable and programmable - so what.

What I'm proposing fits with the rule that both spaces of a switch cannot be occupied at the same time and the rule that occupancy of either space blocks vertical movement through the switch even when that movement would technically be going through the other space in the switch.

To the Knight: I can't allow anything here, but I can say what my point of view is. If we stick to the fact that the squares of a switch should be seen separately, then knight moves ending on the same line are not possible. However, as the game becomes more playable and programmable, compromises should be possible.

We could just say that because of the way that switches affect the geometry of the board, some spaces may be reached by either a vertical move or a Knight move. This would also correct the injustice done to the Knight of making the weakest piece even weaker around a switch while it gives all other pieces greater mobility.

"One last rule change I would suggest is to let Rooks, Queens, and Kings use their ability to move horizontally to switch between the spaces constituting the switch. This would basically involve lifting one more restriction on movement to the spaces making up a switch. "

I have problems with that. I have emphasized that the squares of a switch represent independent squares. This would rather mean that moves between the squares of a switch are possible.

Precisely.

The independence of the squares on the one hand and the functionality of a switch on the other compete with each other. Regarding the direct change between the squares of a switch, I tend towards the superordinate function, so a direct change should not be possible.

Allowing a piece that can move horizontally to move from one space to the other in a switch as a normal move does not affect the functioning of the switch. While the piece is on either space, other pieces can't pass through the switch, and once the piece leaves the switch, pieces will be able to pass through it again.

Just to make sure I fully understand this:

A Bishop on a4 could move along c5-d6-e7-f8 but not b5-c6-d7-e8. For a Bishop on 4 the reverse would be true. But that also means a Bishop on a4 can only be captured from c5-d6-e7-f8 and not from b5-c6-d7-e8.

If this is true the only thing that 'switches' are the connections of 4/a4 to the upper board half. These are either to a5 (f) and b5 (fr), or to a5 (fl), b5 (f) and c5 (fr). And the switch is only in a determined state when 4/a4 is occupied. (And that state has to be chosen as part of the move that occupies it.) When the square is empty you can use all the connections to enter it from above, or to leave it in the same move when you entered it from below.

The intepretation of this that I consider conceptualy the simplest is that 4/a4 is indeed a single square cell, but that the setting of the switch is extra game state. Which can conveniently be indicated by placing the piece that occupies it in the right or left half of the cell, as the distinction only has to be made when the square is occupied. In a computer implementation one could implement the state of the switch through making separate cells of 4 and a4, with only single exits to 5th rank, and duplicate the exits to it from a3 (f), b3 (fl) and b4 (l) so that one connects to 4, the other to a4, both available at any time. But that still would require some 'unnatural' treatment of the spaces 4/a4, to consider one blocked when the other is occupied.

The issue of teh Knight is really an independent one. If the Knight's move is defined 'subtractively', by excluding moves that a Queen can do, its mobility is reduced in the vicinity of the switch, as Q gets extra moves there. In a 'constructive' definition of the Knight move, it would benefit from the switch topology to get extra moves as well.

"A Bishop on a4 could move along c5-d6-e7-f8 but not b5-c6-d7-e8. For a Bishop on 4 the reverse would be true. But that also means a Bishop on a4 can only be captured from c5 -d6-e7-f8 and not from b5-c6-d7-e8.

If this is true the ...."

This is absolutely correct when considering the squares of a switch as separate squares. This looks different if the switch is seen as a unit. But that's a convention that needs to be met. I have already described my intention, but it is not an absolute requirement.

"The issue of teh Knight is really an independent one. If the Knight's move is defined 'subtractively', by excluding moves that a Queen can do, its mobility is reduced in the vicinity of the switch, as Q gets extra moves there. In a 'constructive' definition of the Knight move, it would benefit from the switch topology to get extra moves as well."

Exactly this consideration speaks for a separation of the fields 4/a4. A knight starting from 4 via a5, a6 lands on b6. With a switch as a unit, b6 is on the same line. With 4 as a separate square, b6 is not on the same line. For a4 vice versa. That would be my consideration. I'm thinking of novice players who will notice exactly this inconsistency.

A really constructive discussion, thanks for that. I believe most has been discussed and a broad agreement could be achieved.

During the night I changed my mind on one of my rule suggestions. I had proposed allowing capture of a piece on the occupied space of a switch when a piece moves to the unoccupied space of a switch. This was to fit in with rules regarding no double occupancy of switches and blocking any movement through the switch when one space in it is occupied. These happen to be the most difficult rules to program, and I don't think they're really essential to the concept of a switch. So, I'm going to program a stripped-down version of Chess66 that I'll call Reroute66. This will treat each space as a fully separate space, and the main feature of a switch that I'll retain is that spaces in the switch share some routes to and away from them, and movement from the narrow end can go in either of two different directions. I'll get to work on it later in the day.

It's a pity that reasons for programming are decisive for my variant being downgraded. It is also a pity that the name I have chosen should give way to another name. Does that mean my variant is history? Or have I misunderstood something?

"This will treat each space as a fully separate space, and the main feature of a switch that I'll retain is that spaces in the switch share some routes to and away from them, and movement from the narrow end can go in either of two different directions."

I'm sorry, but I didn't understand that.

As I understand it, Fergus has decided to program a variant based on yours, and given it a different name to signal that it's not the same game. As a game in itself yours remains intact (and probably eventually publishable too if and when the Editorship approves), just more difficult to program given the primitives that Game Courier provides.

This game differs from yours only in that both a4 and 4, or both 5 and h5, can be occupied/passed through simultaneously. As such those spaces connect to the rest of the board in the same way they do already, they just stop being a ‘switch’ in the railway sense (aka a ‘set of points’ in my native British English, or German ‘Weiche’ as used in your original German page) and become just an unusual topological/geometrical feature of the board.

I'll admit I find it a little odd that such conditionally untraversible squares should be so difficult to implement (couldn't it be done with uncapturable dummy pieces that appear and disappear as the other square is occupied and vacated?), but I'm not a programmer and I've never had a go at writing GAME Code, so…

One way to program it would be to have a single square 4/a4, and to introduce a number of extra piece types, each especially adapted to have the moves that the switches would allow. That is, you would have a special Rook for on a3, which would move forward both as a normal Rook, or with a move that switched file after one forward step. (And for a2 one that switched after 2 forward steps, etc.) When a piece of this Rook family would land on an edge file you make it automatically 'promote' to the kind of Rook that belongs on that square. When a Rook landed on a4 there would be a kind of promotion choice: it either stays/becomes a normal Rook, or one that replaces its forward move by a Left-Griffon move. Same idea for the other piece types.

I suppose that through this method I could even have the Interactive Diagram play Chess66. A user-supplied JavaScript function WeirdPromotion would take care of the 'promotions'.

As I understand it, Fergus has decided to program a variant based on yours, and given it a different name to signal that it's not the same game.

Exactly this.

This game differs from yours only in that both a4 and 4, or both 5 and h5, can be occupied/passed through simultaneously.

There are some other differences. Here's a link: Reroute66. The rules are described below the board. I'll add individual piece descriptions to the rules later.

I'll admit I find it a little odd that such conditionally untraversible squares should be so difficult to implement (couldn't it be done with uncapturable dummy pieces that appear and disappear as the other square is occupied and vacated?)

That's the solution I already proposed. But I also think these rules are not essential to the core concept of the game, and I wanted to start with a variant that does not include them.

Does that mean my variant is history? Or have I misunderstood something?

No, it means I am working on my own variant instead of putting pressure on you to change yours. You're free to go with the rules you want for your game. I'll see what I can do about programming it once you have settled on the rules and have described them clearly.

the main feature of a switch that I'll retain is that spaces in the switch share some routes to and away from them, and movement from the narrow end can go in either of two different directions."

I'm sorry, but I didn't understand that.

I mean I am retaining the geometrical properties of the switches, but I am discarding the other rules regarding them.

"...once you have settled on the rules and have described them clearly."

With respect for the great job you are doing, but I can't accept that I haven't set the rules and described them clearly. You can have different perspectives, for example regarding the functionality of the switches. It is also possible to designate parts of it as non-essential. But it is not decisive what can be programmed with the available possibilities. It's a question whether the game can be played with my rules and that the rules are consistent. I had to move concerning the access to the switches because my rules weren't clear. That's it from my point of view. Had to be said. :)

I'm excited to see what happens with my other variants (Chees 69, an addition to Chess 66 and Avatar Chess).

From the questions and expressions of confusion you got regarding what the rules are, it should be evident that you have not described them clearly enough. Also, you seemed to change your mind about some details in the comments. So, you should rewrite your rules to reflect anything you have changed your mind on and to supply the details that someone would currently have to read the comments to find out about.

Here's are some guidelines to use in revising your description of the game.

1. The rules should be made entirely clear in the written text. Illustrations should be used to illustrate what the text has already said, not to provide additional information that is not written down.

2. The text should describe not only what can be done but how to do it.

I have been working behind the scenes to get Game Courier and the drawdiagram.php script to display images better. They can now recolor loaded images for the grid shape, and they can display coordinates above selected boards, which is important for Chess66, because it helps dispell the illusion that a vertical line of movement begins and ends in the same file. Here is the closest it can now come to the diagram that appears in the article. I suppose I should work on options to recolor the pieces, since what I'm doing for this diagram is using a piece set with four colors of pieces and using different labels for all of the Red pieces.

I am very impressed, the changed look in Game Courier is a real enrichment. I am sure that many things can be better represented on this basis. I hope that I am not going too far out on a limb when I say that a variant such as Avatar Chess can be better conveyed. A very interesting upgrade.

I'm looking at the diagrams on my Likebook Mars at night, and on its monochrome e-ink screen, I cannot tell apart the red and blue pieces in the diagrams. At best, they are slightly different shades of black. In the diagram I made, the red pieces, which belong to White, appear even darker than the blue pieces, which belong to Black, which is opposite to how they should look in black and white. For the sake of accessibility for color-blind people and people using e-ink displays or black and white printouts, piece colors with more light/dark contrast would be more suitable.

If I may intrude into the discussion of how pieces are named and refer again to my variant 'Chess 66'. We have discussed Chess 66 and clarified inconsistencies. For my part, I have taken up the suggestions in my description by adding explanations and clarifying examples. The functionality of the switches as I imagine it is not compatible with Fergus 'Reroute 66' (occupied switsches can be skipped, switching between fields of switches is possible). This should be discussed. Therefore I would have the request to publish my variant 'Chess 66'. Are there any reasons against it?

What about 'Chess66'? Do you want to publish it - or possibly not and why not? If you don't want to continue with 'Chess66', then it won't work with 'Chess69' either. Anyway, then try the variant 'Avatar Chess' , which I think is programmable. Thanks in advance.

I didn't really follow the discussion on this variant earlier, but gave the page a fresh read. I think I mostly get it now, except how capturing on a switch works. It might be clarified in the comments, but it should be made plain in the page text as well. (Perhaps it is there too and I have missed it and/or it wasn't quite clear enough.)

Let's say I have a piece on 4, and the opponent has a piece that can otherwise move to a4 but not 4. Can they capture (and if so where do they end their move) or not (if not, could they potentially continue moving through a4 past my piece? I'm not sure that makes sense for any piece at the edge of the board like this, so probably moot, but I'll ask in case)?

Same question reversing 4 and a4. (Now the last question certainly can apply, e.g. the opponent piece is a rook on a8.)

Thanks Ben for the questions, here it should be clearer in the description (although it is already described between the lines, but that is probably not enough).

When capturing on a switch, first assume that there can be only one piece on a switch (here I differ from Fergus Duniho's Reroute66, a variant of my idea). So, for example, if a rook or queen starts from a1...a3 or from rank 4 and the switch is not occupied, then either square 4 or square a4 can be occupied in the switch.

But there is no choice if the switch is occupied by a piece. If a rook or a queen moves from a1...a3 or from rank 4 into the switch, then the piece in the switch must be captured (because two pieces on the switch are not possible). If the piece was on square 4, then the opponent's piece is on square 4 after the move has been executed (applies to a4 in the same way).

Furthermore, an occupied switch cannot be jumped over and a direct change from 4 to a4 (vice versa a4 to 4) is not possible - differently in Reroute66.

Have I understood the question correctly and hopefully answered it correctly? I would be glad.

That helps, yes. To be explicit about the "last" question in each case then, the answer is "not"? My piece on a4 (1) cannot be captured by and also (2) blocks movement (to a1...3) of an opponent rook on a8?

To start with point (2): This is clear that a rook on a8 cannot move to a3...a1 if a switch is occupied.

Regarding point (1), I already had doubts yesterday. According to my imagination so far, the squares of a switch (e.g. 4 and a4) can only be reached from a1...a3 or from rank 4. In my description I assume that a bishop starting from e8 can only reach square 4 of the switch and not a4. This affects a rook/queen on a8 in the same way.

But in this case it means that a move into the switch cannot be done if a piece is on a4, because then the squares 4 and a4 would be occupied together - which would not be in accordance with the rules. But this does not seem very logical.

Therefore, I think that a pragmatic solution for switches should be used.

If the switch should not be occupied, it is possible to move into the switch from above, from below or from the side, whereby either field 4 or a4 respectively 5 or h5 can be occupied.

In case the switch is occupied, the piece in the switch must be captured when the opponent's piece moves into the switch; the opponent's piece takes the place of the captured piece.

This means for your point (1): The rook on a8 can capture the piece on a4, and then it stands on a4.

This also means that a bishop on e8 can reach either square 4 or square a4. If a4 is chosen, then the next move can be towards f8 or towards d1. I think that such an procedure simplifies the rules and makes the game easier to play. What do you think?

Perhaps a remark about 'Avatar Chess'. The variants you mentioned (Lumberjack, Smess) were not known to me before. In normal chess, a piece has a fixed skill level, which means that during the game two kings, two queens, four rooks, etc. define the game. In Avatar Chess it is possible that up to 6 queens, 12 rooks etc. are in play - of course rather theoretically and then only for a short time. I think that this could be interesting.

After contact with Ben Reiniger - see comments below - I have adapted my description of the variant 'Chess 66'.

New is that in switches can be operated as follows: It is possible from below, from above and from the side equally to move into the switch and that independent of the direction of the move the squares of a switch can be reached separately (4 or a4 respectively 5 or h5).

It would be nice if the editors of CVP would read my description again crosswise to finally arrange for a publication. If 'Chess 66' should be published, then 'Chess 69' seems to be published as well.

This is a great idea with those switches. Together with the twisting of the files it makes a very interesting board and game. The switches give instantly the game a dynamic tension which is enjoyable. And a very sophisticated solution that 2 squares together constitute 1 field on which there can only be 1 piece. There is no mentioning of pawn move/capture (maybe it could be helpful), but it must be implied that 'normal' forward movement and diagonal capturing are in place, that will often be first 'battle' around the switches.

What is better than 2 switches? That has to be 4 switches! The inventor, Gerd Degens, has also such a game, Chess69, which can be viewed through the link at the top, or for CVP members through the link in the comments. I will try to make a comment about it later. But I can only recommend to the editors that this game also is published properly. It is even more interesting because here the ranks are also twisted, very delightful for us fans of 'unusually shaped boards'. It already has a old post from 2003 here on CVP with a broken link in the Alphabetical Index and the Topic Index, so that will have to be displaced.

Thanks Thor for the flowers. For those interested: Chess69

@ Fergus Duniho

Thor Slavensky wrote on 2022-10-23 CEST   Good ★★★★
This is a great idea with those switches. Together with the twisting of the files it makes a very interesting board and game. The switches give instantly the game a dynamic tension which is enjoyable. And a very sophisticated solution that 2 squares together constitute 1 field on which there can only be 1 piece. There is no mentioning of pawn move/capture (maybe it could be helpful), but it must be implied that 'normal' forward movement and diagonal capturing are in place, that will often be first 'battle' around the switches.

What is better than 2 switches? That has to be 4 switches! The inventor, Gerd Degens, has also such a game, Chess69, which can be viewed through the link at the top, or for CVP members through the link in the comments. I will try to make a comment about it later. But I can only recommend to the editors that this game also is published properly. It is even more interesting because here the ranks are also twisted, very delightful for us fans of 'unusually shaped boards'. It already has a old post from 2003 here on CVP with a broken link in the Alphabetical Index and the Topic Index, so that will have to be displaced.

Chess 69 is the follow-up to Chess 66; Chess 66 has already been published properly. Thanks in advance.

This game has a paradoxical nature, because some pairs of independent spaces also function as though they are the same space. Due to this paradoxical nature, confusions about the rules can easily arise. This makes it all the more important to clarify the rules in detail. It is not enough that the rules seem clear and complete to its creator. The standard to be met is that they seem clear and complete to other people, and particularly to programmers, who have to anticipate every possible move ahead of time.

Here are some examples that are not handled clearly enough in the description of the rules. The following diagram shows legal moves for the Bishop on c1. It can move to 4, though not to a4.

This diagram shows its legal moves a few moves after it has moved to 4. At this point, it may move to b3 but not back to c1. Is this all correct?

As I understood it only the second is correct. All moves are reversible in this game (except for Pawns, of course). The squares a3 and 4 have an edge in common, so going between those would be an orthogonal step, not allowed for a Bishop. Both 4 and a4 connect diagonally to b3, as they both have only a corner in common with the latter. (Not clear from the picture is that 4 and b4 share an edge.)

The Interactive Diagram I posted in the Chess69 topic thread (which has a similar switch) should show the correct moves for Bishops and Rooks. (Not for King, though!)

It makes sense that all paths for Bishops and Rooks should be two-way. In this case, I neglected to unlink 4 and 5 from spaces they got diagonally linked to with map. It would help to add the following to the rules to help clarify things:

1. Every path of movement for a Rook, Bishop, Queen, or King can go either way. So, for any two spaces, x and y, if one of these piece is normally capable of moving from x to y, it is also normally capable of moving from y to x.
2. Orthogonal and diagonal paths of movement are mutually exclusive. Orthogonal movement is permitted between spaces sharing a side, and diagonal movement is permitted only between spaces that share a single corner but no sides. So, between 4 and a4 or between 5 and h6, only orthogonal movement is allowed, and between 4 and b3 or between 5 and h6, only diagonal movement is allowed.

Now, based on these, it would be legal for a Queen (or Bishop) on g6, as illustrated below, to move to either h5 or 5. Is this correct?

To reduce the illusion that 4 and 5 are diagonally adjacent to a3 and h6, I have modified the board to use alternating horizontal lines of both colors in half of 4 and 5 instead of using a dividing line. This makes it look more like each pair of spaces in a switch are actually overlapping spaces.

That indeed removes the impression that the triangular edge parts of 4 and 5 are cells in themselves, which diagonally border a3 and h6. For the same reason I had used the same special color for all of 4 and 5 in the Interactive Diagram. In the rectified representation a4 and h5 are not distorted, and the shape is enough to suggest that they do form complete squares partly hidden under 4 and 5.

The Queen move looks fine to me.

This diagram shows its legal moves a few moves after it has moved to 4. At this point, it may move to b3 but not back to c1. Is this all correct?

The move options shown are correct.

The possible moves of a bishop on 4 go in the direction of d1 or e8, but not to a3, b2 or c1.

Here are some examples that are not handled clearly enough in the description of the rules. The following diagram shows legal moves for the Bishop on c1. It can move to 4, though not to a4.

These moves are not possible.

The bishop on c1 can move to a3, but not into the switch. The bishop on 4 can in principle move to d1 or e8. The moves to a3, b2 or d1 are not possible. The queen on d1 can reach the switch - provided there is nothing in between. In the switch, the queen can be on 4 or a4.

Now, based on these, it would be legal for a Queen (or Bishop) on g6, as illustrated below, to move to either h5 or 5. Is this correct?

That is absolutely correct. The move possibilities of the queen are shown completely.

After the discussion at that time I have adapted my description. In summary it says:

• Finally, you can move into a switch from below, from the side or from above. If the switch is not occupied, then you can choose whether the piece that moves into the switch is on 4 or a4 respectively on 5 or h5 after the move. If the switch is occupied, then the piece in the switch must be captured; the opponent’s piece takes the place of the captured piece.

Using alternating horizontal lines in both colors in half of 4 and 5 instead of a dividing line seems to be a good solution.

Does a Pawn on a2 or h7 have an option concerning which space it goes to in a double move? If so, details about this and the effect it has on en passant should be included.

Does a Pawn on a2 or h7 have an option concerning which space it goes to in a double move?

Yes, that is how it should be. A pawn must also have a unique position in the switch - 4 or a4 / 5 or h5. I think it is logical if this applies to all pieces in the game.

If so, details about this and the effect it has on en passant should be included.

You mean the description? If so - I want to wait for more tips, and then revise the description.

The concept is expandable. At the maximum, it could look like this:
 

In this level, 16 new squares would be created. The game could then be called Chess 80, or in another notation Chess 64/16. Of course, intermediate levels between Chess 66 and Chess 80 are conceivable.

In the following example, moves can be made not only forked as in Chess 66, but triple-forked moves become possible.

Such an extended concept certainly leads to the question of playability. But it might be interesting to think about it.