Comments by tlarsonfreeman

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.

(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

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.

I've updated the rules, separating the rule for threefold repetition from the the one for a 50 turn and a 75 turn rule. I've also made the change I mentioned below for the rule on notation. (One could argue that a description of notation doesn't really belong in the rules section, but I'll leave it there for now.)

Thanks.

Thanks for your review, Greg. You have understood the design perfectly, and I would be delighted if you added Two Move Chess to ChessV!

After some thought, I see that the rule for three-fold repetition should be handled differently than the 50 move and 75 move rules. Let's take them one at a time.

For threefold repetition, let's consider the game to be a sequence of board positions. A two move turn results in two positions, while single move and response move turns result in only one. It doesn't matter what type of move produced each position--a player may claim a draw by threefold repetition simply by noting that a certain position has been reached for a third time (with the usual considerations of whose turn it is, what castling rights exist, etc.).

For the 50 move and 75 move rules, I think the simplest resolution would be to change them to a 50 turn rule and a 75 turn rule in Two Move Chess, with the reminder that a turn and a move are not equivalent.

I am open to other proposals, for example these rules could be replaced by a "25 turn rule" and a "38 turn rule", but I am inclined to think that would introduce unnecessary confusion.

Thanks, Fergus. I see your point about notation. Upon reading it through again, I think it would be more clear if the rule explained up front that it is just about notation. I'd like to update the first sentence to say, "When recording a game, a two move turn must be clearly distinguished from the moves of the other player."

Thanks for updating the name of this variant in the database, Fergus. And thanks to everyone for the additional comments below. I have added a paragraph to the introduction to explain the motivation of the design. I hope this will make it easier to understand the reasoning behind each of the rules.

This submission is ready for another review. My hope is that it is now ready to go!

Thanks.

Ted

Actually, maybe it's better to let the comments go. I can create a new submission with the name "Two Move Chess" and delete this one. Earlier I was thinking we should preserve the comments to give credit to both of you for the clarifying discussion and for the suggested name change, but I also don't want to make extra work. What do you think?

Thanks.

Ted

After some thought, I would like to change the name of this variant to "Two Move Chess." If it's not too much trouble, it would be nice to rename it while preserving the comments.

I have gone over everything again and made additional minor edits that I hope clarify the rules. I have also added an example of stalemate in the Notes section, and added a note at the start of one of my earlier comments that was both unclear and incorrect, letting people know that they should disregard that particular comment.

Thanks again for all of the comments, questions, and suggestions below!

Ted

I have just edited the rules. I split them up into more numbered items, and (I hope) added clarifying language. Thank you for the comments and questions. Please take another look.

I am still pondering the question of the name. If I change the name, will the URL change? And if so, would we lose these most excellent comments?

Thanks.

Ted

That's a great suggestion! I might be more inclined to "Two Move Chess", but I like it either way. Thanks for the suggestion.

Okay, let me see if I can explain my thinking here. The terms "turn" and "move" are not interchangeable in this game. The rule for stalemate could be stated most simply as: the game ends in stalemate if at the start of a player's turn he is not in check and cannot complete a legal turn.

To break that down, assume that the player is not in check. At the start of his turn the game is in one of two states:

1. His opponent has just made a single move. In this case he must make a response move. Since this is just one move, the possibility of stalemate is evaluated exactly as in international chess.
2. His opponent has not just made a single move, so he may take a two-move turn (if possible) or a single move turn (if possible). Keep in mind that the set of moves that could comprise the first move of a two move turn is disjoint from the set of moves that could be played in a single move turn. If none of the moves in the first set can be followed by a second legal move, and the second set is empty, the game ends in stalemate.

When you ask above, "what if the first move is one that would normally prohibit a second move, such as a check, a promotion, a capture, or a double Pawn move subject to en passant?" you are asking about a possible single move turn. It is not stalemate if any such move is available.

I am trying to be succinct, and yet it seems I need to provide more detail here.

This is a fair point. I am open to suggestions on the name. Initially I wanted to use the name "Double Move Chess" and was quite disappointed to find that the name was taken. I clearly failed to do another search, as I was unaware of "Chess2 - The Sequel" until now.

I like "Chess2" because of the double meaning of it being the second version of the game as well as it being characterized by two-move turns. The alternative "Chess2.0" would sort of lose the second meaning.

But you're right, this needs a new name. I will try to think of a better name, and again, suggestions are welcomed!

Thanks.

(Note: my answer below is not clear and not quite correct. It is also out of date--the rules have been renumbered and it should now refer to rule #2. Please disregard this answer and see the full rules and subsequent discussion above.)

Okay, I see that I need to clarify this rule. To answer each of your scenarios:

1. By rule #1, each move of a two-move turn must be individually legal for the position on the board at that moment--it does not matter whether a second move could remove any checks caused by the first move. So if there is no legal first move, it is stalemate.
2. This is stalemate.
3. This is also stalemate.

Would this wording be more clear?

The game ends in stalemate if at the start of his turn a player is not in check and cannot complete either a legal two move turn or a legal single move turn.

This submission is now ready for review. Thanks!