3 ms·

I think I would specify that a move has to be legal when at the start of the move, i.e. while it is being written down.

• williamdclt 6y ago
  Or alternatively, the piece doesn't move if the move turns out to be illegal? Would have to try both options to see which works better
  • lisper 6y ago
    That would open up the possibility of a paradoxical situation where both moves are legal at the start but neither is legal at the end.
• Someone 6y ago
  So, a king could move into a checkmate, even if it wasn’t in check at the start of the turn. Seems fine to me, but I think it would be funnier if a king in check could stay put, with the player in check betting that the opponent’s next move will end the check. There also is the possibility of simultaneous checkmate. Another edge case is pawns taking pieces. Could a pawn move diagonally into a square being vacated by the piece standing there? Could two pawns simultaneously not take out each other (say by the simultaneous moves d4×e5 and e5×d4)?
  • lisper 6y ago
    > a king in check could stay put, with the player in check betting that the opponent’s next move will end the check. Yes, that was part of the intent. There is game theory in play as well as chess strategy. > There also is the possibility of simultaneous checkmate. Yes, or even simultaneous king capture without checkmate(s) resulting in a draw. Or you could adopt a quiddich-like rule and say that if the kings are simultaneously captured then the game is decided by the sum total of the remaining value of the pieces on each side. > Could a pawn move diagonally into a square being vacated by the piece standing there? Could two pawns simultaneously not take out each other (say by the simultaneous moves d4×e5 and e5×d4)? I would say yes and yes.