Ratings & Comments

"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.

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.

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?

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.