Remove the rule, update the book

I have removed the rule which stated that the first piece in a move cannot return to its initial position, regardless if it was the only piece in a move, the first in a cascade, or in divergence. Since this is a major change I'm also updating the book, the other changes include:

• clarified double checkmate, added notation and status grammar,
• reworded Starchild intro,
• clarified castling notation, fixed grammar,
• clarified optional notation, fixed outro,
• reorganized sections, 
• fixed formatting in tables, 
• other tiny fixes.

If the rule stayed, it would actually mean that all pieces would have to be uniquely tracked, which would mean that each piece would have to be assigned unique number at a start of a match, and then for everything else it's type and tag would have to be fetched from look-up-table. This would lead to a major  shift of underlying API in a library; but more concerning, also in paradigm shift, where chessboard wouldn't host pieces anymore, but their unique identifiers. This change would be even more of a tectonic shift than the previous one; doable, but got me thinking; is it really worth it, why did I impose such a rule, and such.

For one, it wasn't a movement rule per se (belonging to any particular piece), but it was a restriction imposed on a movement rules of all pieces. As such, it doesn't belong in the book, but among other FIDE or tournament rules. More specifically, any piece starting a move cannot do anything more than just to initiate a permutation of Waves, if that starting piece is about to return onto its initial position in the same move. What I overlooked is that permutation necessary leads to repetition of positions, and that has already being handled by FIDE; for instance, see FIDE 9.2 point in FIDE Handbook.

Another reason for the removal of the rule is physicality; all pieces of the same color and type look the same; this is especially true if displayed on-screen, on a web site, or in a computer game. And yet, the rule called for recognizing (and accounting for) that one specific e.g. dark Rook which started a cascade vs. the other(s) which did not. Of course, computers can be programmed to distinguish those easily; however, a player would have hard time tracking which dark Rook is which, especially in a long-winded cascade.

In short, the above rule would be difficult to implement, goes against a physical reality of a game it tries to regulate, and there is already available better, easier alternative; so, no wonder it has been removed.

Anyway, the book was compiled on June 6, 2025, version is 20250620.014531, and can be found behind that juicy red button above, or in other usual places.