H. G. Muller wrote on Fri, May 1, 2020 01:42 PM EDT:
I would like to propose a definition of 'pass through check' as "passing through or jumping over a square where it would have been illegal to move your royal to, had that square been empty".
I see the current glossary doesn't contain a definition for 'check'. One could define it as a situation where a royal could be pseudo-legally captured if the player currently on move would pass his turn. But there could be a variant 'Recursive Chess' where it is not allowed to capture a royal when it exposes your own King. So it is perhaps better to define a legal move as a pseudo-legal move that does not expose your royal piece to capture, with the note that a move that terminates the game would never expose anything. Some game-termination rules are such that the actual game result is determined by an 'after-move': E.g. in Shatranj you can win by baring the King, unless the opponent can bare your King in the next turn (in which case it is draw). Or, presumably, when he could capture your King (in which case you would lose by having played an illegal move). So on King baring, he gets an after-move. Variants like King of the Hill allow you to make the winning move to the center only if that move was legal, i.e. reaching the square is not enough, but there is an after-move that reverses the result when it can capture your King. And in Tai Shogi the royal is an Emperor, which can capture to any square on the board. Except that he cannot expose himself to recapture when capturing a royal. So there is an after-move in Tai Shogi even after capture of the royal, and the capture of the Emperor in this after-move has priority in deciding the game result over capture of the first royal! Recursive Chess could also be formulated that way.
So you are in check if the opponent, would it be his turn, has a winning pseudo-legal capture on your royal piece. In orthodox Chess any capture of the King would be instantly winning. But in Recursive Chess capturing the King with a pinned piece, (or in Tai Shogi capturing a protected Emperor with your Emperor) would be a losing capture, as in the after-turn your own King would be taken. So you would not be in check when you expose your King to capture by a pinned piece (or when your Emperor is protected). In al cases this can then be combined with the rule that moves that put your own royal in check are illegal.
I would like to propose a definition of 'pass through check' as "passing through or jumping over a square where it would have been illegal to move your royal to, had that square been empty".
I see the current glossary doesn't contain a definition for 'check'. One could define it as a situation where a royal could be pseudo-legally captured if the player currently on move would pass his turn. But there could be a variant 'Recursive Chess' where it is not allowed to capture a royal when it exposes your own King. So it is perhaps better to define a legal move as a pseudo-legal move that does not expose your royal piece to capture, with the note that a move that terminates the game would never expose anything. Some game-termination rules are such that the actual game result is determined by an 'after-move': E.g. in Shatranj you can win by baring the King, unless the opponent can bare your King in the next turn (in which case it is draw). Or, presumably, when he could capture your King (in which case you would lose by having played an illegal move). So on King baring, he gets an after-move. Variants like King of the Hill allow you to make the winning move to the center only if that move was legal, i.e. reaching the square is not enough, but there is an after-move that reverses the result when it can capture your King. And in Tai Shogi the royal is an Emperor, which can capture to any square on the board. Except that he cannot expose himself to recapture when capturing a royal. So there is an after-move in Tai Shogi even after capture of the royal, and the capture of the Emperor in this after-move has priority in deciding the game result over capture of the first royal! Recursive Chess could also be formulated that way.
So you are in check if the opponent, would it be his turn, has a winning pseudo-legal capture on your royal piece. In orthodox Chess any capture of the King would be instantly winning. But in Recursive Chess capturing the King with a pinned piece, (or in Tai Shogi capturing a protected Emperor with your Emperor) would be a losing capture, as in the after-turn your own King would be taken. So you would not be in check when you expose your King to capture by a pinned piece (or when your Emperor is protected). In al cases this can then be combined with the rule that moves that put your own royal in check are illegal.