Because of the asymmetry of this variant it required some special attention to make sure the diagram would only allow each side to promote to its own pieces. What I did was define the promotion choice with an asterisk before each piece, meaning it can only come from the holdings. Then I stuffed the holdings initially with eight of each eligible piece type (enough to promote all Pawns to it).

Except for the Spartan King, which would only be a valid promotion choice if one of the Kings was captured. So I defined the holdings type such that it would accumulate captured pieces of the original owner. By starting without Kings in hand the Spartans then can only promote to King when one of their Kings is captured.

Castling

Only the Persians can castle, and this forced the Persian and Spartan Kings to be defined as different piece types. (If castling is specified with the aid of an O atom, the diagram assumes it is with a Rook or a corner piece of any type. And we do'nt want the Spartan Kings to castle with their Lieutenants!) This has the dubious effect of the Spartan Kings not being considered royal (as the diagram only considers one piece royal, by default the last one defined). So moves of Spartan Kings into check are not 'grayed out', like they are for the Persian King. But of course this is justifiable, as the Spartan King can actually expose itself to capture (if there still is a second one). So such moves can be legal. The diagram does not understand extinction royalty.