> 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 i

> 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.