Is there really no better solution for this? Extra fields should be avoided as much as possible, and I don't like the use of the extra + at all. E.g. WinBoard treats the castling field in Seirawan Chess as a general rights field, (indicating the virginity of all back-rank pieces, from which gating and castling rights follow), by mentioning their file.
The same could be done here: initially the Bishops would be in the rights field, as they can convert. If one converts the rights for both disappear. If one fails to convert on its first move, its conversion rights disappear. The rights that remain for the other now become an obligation. If the first Bishop is captured in the virgin state, you could leave its rights, implying that conversion of the one that is still there is still optional.
Or you could write an X in the rights field to indicate an undetermined conversion right exists. The X changes into the Bishop file ID to indicate that Bishop must convert, or disappears when no more conversion is allowed.
Is there really no better solution for this? Extra fields should be avoided as much as possible, and I don't like the use of the extra + at all. E.g. WinBoard treats the castling field in Seirawan Chess as a general rights field, (indicating the virginity of all back-rank pieces, from which gating and castling rights follow), by mentioning their file.
The same could be done here: initially the Bishops would be in the rights field, as they can convert. If one converts the rights for both disappear. If one fails to convert on its first move, its conversion rights disappear. The rights that remain for the other now become an obligation. If the first Bishop is captured in the virgin state, you could leave its rights, implying that conversion of the one that is still there is still optional.
Or you could write an X in the rights field to indicate an undetermined conversion right exists. The X changes into the Bishop file ID to indicate that Bishop must convert, or disappears when no more conversion is allowed.