Comments/Ratings for a Single Item

Michael, you are nearly correct. If a player is reduced to a bare king and is not in check, the only way it would not be stalemate on his turn would be if the king could capture an opponent's piece, or if his opponent has just taken a single move turn and the king still has a legal move available.

See Example 4 in the Notes section. Also, consider the position at the end of the game in Example 5. If play were to continue it would lead to stalemate as soon as Black captures or blocks the advancing pawn (unless White is in a position to immediately capture Black's pawn or bishop).

Because of this, players need to carefully consider endgame positions to make sure not to inadvertently end a game in stalemate.

(Note: I have edited my answer below to improve the example.)

You make an excellent point, H.G. I will adjust the rule for threefold repetition to state that the positions are only considered equivalent if the entire state of the game is the same (e.g. if a position occurs half-way through a two move turn for Black and the same position is repeated later at the start of a turn for Black, those two positions would not be considered equivalent).

Your second point is thought provoking. The existence of the threefold repetition rule in international chess does provide a target for a player who is behind to still achieve a draw. My goal with Two Move Chess is to alter the game as little as possible while eliminating (or at least reducing) White's first move advantage, so I think we need to keep the rule.

Thanks.

Ted

Here's how the double-move variants in ChessV currently work.  (I don't think other variants have specified how 50-move and draw-by-repetition should work.)

Any position can be a repetition, including the first move of two, but will only match positions with the same move status.  So the first move of two will only match another position with the first move out of two (and same castling, en passant privs.)

For the 50-move rule, every individual move counts.  So a two-move turn could add two to the count.  (Internally, ChessV is built for individual moves.  The double-moves are accomplished by altering when the side-to-move flips.)  I'm not sure how hard this would be to change.

I also think, in general, that repetitions and 50-move draws aren't likely to happen in double-move variants.  Even with the one capture per turn limit, the game should still be pretty violent.

Thanks for the explanation of how ChessV works, Greg. I have rewritten the description of the rule for threefold and fivefold repetition to take into account the feedback below. I believe the way ChessV handles it will work, with just one thing to clarify. The move status in Two Move Chess is one of these:

1. It is the beginning of a turn that is not a response move turn
2. It is half way through a two move turn
3. It is a response move turn

In ChessV, you might have to do something to ensure that otherwise identical board positions with these distinct possibilites for move status are not considered the same.

For simplicity, I would like to leave the 50 turn and 75 turn rules as they are. The 50 move rule in international chess considers 100 board positions, for example, and I think it would be unnecessarily confusing to have a "100 position rule" and a "150 position rule" in Two Move Chess. I agree that these rules will almost never actually be invoked in Two Move Chess.

I am also open to persuasion if this proves to be a stumbling block in ChessV.

I have posted Python code that validates games of Two Move Chess on Github at https://github.com/tedlf/two-move-chess.

This code leverages the python-chess module. In addition to validation, it was used to generate the board images used in the examples in these rules.