2 | Both players play a move "at the same time".
3 | Conflicts are resolved following a few simple rules.
6 In order to not rethink a big part of the code, the white move has to be
7 played before the black one. However, the black player doesn't see it.
9 p So both players play "at the same time". Resolving rules:
12 If both moves arrive on the same square, both pieces disappear except
13 if one is a king. In this case only the king remains.
15 If a capture was intended but the target moved, the move is still played
16 but doesn't capture anything.
18 Such captures can be anticipated by capturing our own pieces.
19 If the enemy captures as predicted, his piece disappears.
20 If he doesn't, the self-capture isn't undone.
22 figure.diagram-container
24 | fen:rnb1kbnr/ppp1pppp/8/3qP3/8/8/PPPP1PPP/RNBQKBNR:
25 figcaption After 1.e4 d5 2.e5 Qxd5 (anticipating 2.exd5 which isn't played)
30 Due to the simultaneity, it is possible that a king is captured for example
31 after escaping a check in a wrong way, as the following diagram shows.
32 So, capturing the king counts as a win, of highest priority.
33 A checkmate wins too, but if your king is captured and the other still on
34 the board (even if it is mated), you lose.
36 figure.diagram-container
38 | fen:r3r1bb/ppqRkppp/8/2p1n3/7n/8/PPPPP1P1/RNBQNBK1:
40 | fen:r3r1bb/pp1qRppp/8/2p1n3/7n/8/PPPPP1P1/RNBQNBK1:
42 Left: before Rxe7 (white) and Qxd7 (black)
43 Right: after the move (1-0)
48 a(href="http://www.hexenspiel.de/engl/synchronous-chess/") Synchronous chess
49 | , modified to allow en-passant captures
50 | and disable the "exchange of captures" stage.
51 a(href="http://www.pion.ch/echecs/variante.php?jeu=synchro") Another description