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Type selectivity is provided by means of the captureMatrix, possibly in combination with the apostrophy in the XBetza to restrict it to a subset of the moves. I haven't encountered any case yet that could not be handled this way.

Type selectivity is provided by means of the captureMatrix, possibly in combination with the apostrophy in the XBetza to restrict it to a subset of the moves. I haven't encountered any case yet that could not be handled this way.

But what if the qualification only affects one of a group of possible moves? In this case, the opening move of a Pawn, which could capture anything with its conventional capture but has a special initial move only for capturing nearby enemy Pawns.

You would forbid the capture of all non-pawns by pawns in the captureMatrix, and then exempt the pawn's normal captures from this restriction by suffixing it with an apostrophe.

What would not be possible is having some moves that can only capture pawns and others that can capture only knights. (So you cannot implement an Ultima Chamelion with this method.)

You would forbid the capture of all non-pawns by pawns in the captureMatrix, and then exempt the pawn's normal captures from this restriction by suffixing it with an apostrophe.

Wouldn't this mess up Pawn promotion?

@HG: I thought I had understood, but finally I'm confused and lost. I try to describe Rhino (TwiKnight) (and Mirror-Rhino (KnightTwi)) in Betza's notation. I found z(FW) in an old page (made by Betza) but it doesn't work on the diagram. Maybe the role of the () has changed.

Also I don't understand why when I test zW and zR, I get the same result. Is z meaning an infinite repetition?

Is all this consistent?

Rhino: (afz)W
Snake: (afz)F
z stands for zigzag & it's repetition depend on the board size. This page is about XBetza notation, not Betza notation.

I did know about Betza's t[FR] proposal for Griffon, but I had never seen this z(FW) notation. XBetza is only upward compatible with the Betza notation for simple ('single leg') moves, and has its own system for combining these to multi-leg moves, which is more general than any of the suggestions that Betza coined in various scattered places.

The z modifier applied to a slider atom is original Betza notation for a crooked version of the piece, and is still supported in XBetza. On a leaper, such as zW, it never had any meaning.

The role of parentheses has completely changed; in XBeza these indicate zero or more repetitions of the enclosed group. So z(FW) would mean zzFWzFWFWzFWFWFW..., which doesn't really mean anything.

Brackets originally were not used in XBetza, but legs of a move were 'chained' by using an a as separator between the modifiers of each leg. This does the job of unambiguously defining very complex moves, but often leads to a very obfuscated description unsuitable for human digestion. A much clearer notation is possible by using brackets (but in a way that somewhat is different from Betza's t[...] construct). The brackets still enclose a sequence of simple Betza moves, which are supposed to be played in that order. But there is no t prefix (which was redundant, because the brackets are never used for any other purpose than chaining the contained moves), and separates the enclosed moves by hyphens (if continuation is mandatory) or question marks (if the move could also end there). This notation is already supported in the Interactive Diagram for simple cases like the Griffon ([F?R]). Supporting it in its full glory is a desire for the future.

The meaning of z in a multi-leg move has also changed; it now means l or r, but the opposit of what the previous leg did. (So that it can be used to specify crooked paths, while q means l or r in the same direction, and can be used to define curved paths.)

@HG: somewhat it gives me some explanation, somewhat I'm more confused than before. So, HG, taking this "The meaning of z in a multi-leg move has also changed; it now means l or r, but the opposit of what the previous leg did. (So that it can be used to specify crooked paths)"; how would you write that Betza's Rhino and Mirror-Rhino?

@Haru N Y: your notations do work but I can't understand why. Indeed I belong to those not digesting the "a" at all. And why do you call the Mirror-Rhino a Snake? That confuses me even more too.

You should consider the a as a chaining symbol, separating the modifiers for the legs of a multi-leg move. So in afsafzafzW you see 3 a, which means the move has 4 legs. The modifiers for these legs are none, fs, fz and fz, respectively. So the first leg is a W move in all directions (no modifier). From there it continues forward-left or forward-right (because s = l or r), i.e. a diagonal step in the second leg. Then for the third leg it again deflects 45 degrees, but in the opposit direction as in the second leg, as this is what z means. Etc. So afsafzafzW is a shorthand for aflafraflWafraflafrW, two crooked trajectories that are each other's mirror image.

Haru's notation (afz)W is shorthand for WafzWafzafzWafzafzafzW..., a set of ever longer crooked trajectories. Every additional afz adds a new leg, which deflects in the opposite fl or fr (relative) direction as the previous leg did. (Which is the hallmark of a crooked move; if they would all deflect in the same direction, which you could do with fq, you would get a circular piece.)

The second leg in every sequence should really have been specified as fs, however, to indicate it can deflect in both directions, rather than only in one that is specified relative to the previous one. The first z or q occurring in such a sequence (i.e. before it is clear what 'opposit' or 'the same' direction means for the deflection, because there was no previous deflection) is always interpreted as s. You could see this as a special rule for expanding the parentheses into paths with different lengths.

Indeed I belong to those not digesting the "a" at all.

Think of a as a separator between two legs of the move, like an "and". In aW, the a implies that there are 2 legs and the W tells you what those legs are.

It would probably have been clearer if I had used a hyphen or slash instead of an a. But it all started as aaK for the area move of Tenjiku Shogi, and caK for the Chu-Shogi Lion. But the hyphens seem to group the atoms in the wrong way, when you don't also use brackets around the individual moves.

In (not-yet-implemented) bracket notation the Betza Rhino would be [W(?fzK)], shorthand for [W?fzK?fzK?fzK?fzK?fzK?fzK?fzK...], a W leg followed by any number of alternating fl and fr K steps.

@Daniel, HG. Thank you for your kind explanations. I start to see better. I had not caught the fact that the "a" could link with a "none" modifier.

I understand the logic. I don't like it much though. It is strange that nothing more natural could have been imagined, without ambiguity, to chain simple moves. You guys have been thinking on it for a long time, so I guess it is not so easy.

Well, the bracket notation is simpler. This is why I would like to switch to it.

But when chaining moves into a single path it cannot be avoided that you would have to specify the bending angle at each point where two legs connect with the aid of directional modifiers (if f is assumed to be default).

And there is the more fundamental problem that oblique paths occur as pairs of mirror images, and that this mirroring swaps the meaning of l and r. To avoid having to specify complex oblique paths twice, there must be a way to encode sideway deflections not as an absolute direction, but in a relative way. And this is what z and q do.

I can't seem to en passant fnafsmW.