Popeye 4.77: a new release, 24.05.2017

Definition Lost Pieces:
Nach jedem Zug werden alle Steine der gegnerischen Farbe automatisch vom Brett entfernt, sofern sie von der ziehenden Partei beobachtet sind und sie sich einer feindlichen Beobachtung nicht entziehen können.

After each move all pieces of the adverse colour are automatically removed from the board provided they are observed by the moving party and they cannot evade hostile observation.
THIS WAS THE “NEW” FAIRY CONDITION IN THE ANDERNACH COMPOSITION TY. MAY 2017.
RESULTS IN THE NEXT feenschach. best by -be-

Popeye’s “help anymove” command is very useful for answering such questions. In this case the code is:

stipulation h~1
pieces
white pb5c5
black pa7a6 qh1
condition LostPieces
option HalfDuplex

The first two solutions given by Popeye are:

1.b5-b6[-bPa7] Qh1-a8
1.b5-b6[-bPa7] Qh1-b7[-wPb6]

So after 1.b5-b6 the bPa7 is removed immediately, before Black plays his move. The same thing occurs even if the wK is added on b2, even though 1…Qb7 pins the observing white unit.

The participants in Andernach this year found the description by Popeye maestro Thomas Maeder helpful:
After each move, you check the adversary’s pieces one by one, each time on the assumption that the piece under consideration is royal and is the only royal piece on the board. If that piece would then be mated, it is marked for deletion – and when all the adversary’s pieces have been checked in this manner, those marked for deletion are removed from the board before the other side is to move. (This implies that there are no chain reactions: if White plays Ra5 in a position with black Pb5d5 and white Pb4d4, only Pb5 is removed at this time – Pd5 may be removed next time, if the position is the same.)

The method described (which is the one Popeye actually uses) also implies that if there is a bKa5 in Geoff’s example, bPa7 would *not* be removed! It could be saved by Kxb6, because Ka5 is considered non-royal when Pa7 is checked for possible deletion.