Enter Your Reply

I knew that the move-priorities-trick does not work. Zillions resolves
move-priorities before the checkmate condition. So it first concludes
there is a normal move and then thus renders the special move illegal
versus the move-priorities. And then it renders all normal moves illegal
because of check. A possible solution is to take into account that
defenders can be pinned by Bishops, Rooks, Dragon Horses and Dragon Kings.
It is easy to implement (A defending capture move is either like a Bishop,
like a Rook or like a forwardmost Knight, the relative position of the
mating Pawn with respect to the mated King is fixed. This leaves six
pinnable positions for defenders (four diagonal and two orthogonal).

However, this does not solve the problem. It just reformulates the Pawn
drop rule to 'A Pawn may not be dropped to check the enemy King when ...
(long formulation involving the geometric explanation of some specific
pins) ...'. It should be 'A Pawn may not be dropped to give checkmate'.
In Shogi these rules may have the same effect, but it doesn't give a
checkmate-detection that always works. If someone wants to use Shogi.zrf
to make a Shogi variant with some different pieces, he or she can never
know that the Pawn Drop Mate rule is well implemented. The same problem is
there for Tamerlane 2000, where Princes can become Kings when the original
King is mated (It is not implemented because detecting checkmate in
Tamerlane 2000 is a nightmare). Another example is 'Thirty-Nine squares
Chess' where you may leave your King in check, but you lose if you are
mated (Kings return when captured). I have an ugly solution for the last
example, but the ZRF is still too ugly and buggy to publish.

A (dirty) solution would be that the Pawn Drop Mated player can declare
checkmate after a pawn drop. On such a declaration, the whole position if
flipped (A Black Gold on 3f becomes a White Gold on 7d, etc) and the
player that dropped the Pawn is automatically checkmated if it were
checkmate, but that player should win the game if he or she can continue
with a legal move (Penaly for a false declaration). It takes a while to
implement. You have to know whether the opponent just did a Pawn drop, the
flip mechanism must be implemented. The flip must be registered (for
instance by dropping a Sign piece on a dummy position). These Sign pieces
should also enable a 'death penalty'-move if the dropping player manages
to prove that it isn't checkmate. Anyway, it really fucks up the ZRF just
to use the (checkmated ...)-command in a different context then ending the
game.