Single Comment

Harm, according to your Superchess note I ask, whether the implementation
of those four piece types: Amazon (Q+N), Empress (R+N), Princess (B+N) and
Veteran (K+N) would be suffcient. It presume that it would not be
important, to name those piece types differently in SMIRF/Octopus:
Archangel (A = B+N), Centaur (C = R+N), Giant (G = Q+N) and Hydra (H =
K+N) thus defining new unique letter symbols for those types.

But still I see some problems in defining a compatibly extended X-FEN
because of the differing promotion behaviour, which could be derived from
the whole game only. Additionally it is unclear to me, how those first
PRELUDE moves have to be encoded (PGN/algebraic). Moreover it is not
clear, whether castling rights would be occupied by super-piece
replacements or not.