# Longest sequence of unique legal moves for one player, always in check and ending in checkmate

I recently played a bullet game, in which I thought I was in checkmate, but then realized I had one legal move, this then repeated again and again 6 times until ultimately I was in checkmate. I share this anecdote as an explanation for the seemingly arbitrary parameters.

To reiterate, one player (black or white) puts the other player in check. That player has only one legal move (moving the king, blocking the check, or capturing the attacking piece) Then the other player puts them in the same circumstance of one legal move. Player one does not need to be put in check or have their moves limited, only in the sense that no positions may be repeated.

The final check of the sequence is checkmate.

• To be clear, are repeated positions allowed or do you want the checking player to have to make a move that results in a different position each time? Depending on your answer, I can be real crafty with the 50 move rule and threefold repetition. Commented Mar 5, 2023 at 21:17
• Hello Rewan, to clarify, no repeated positions are allowed. The purpose of this challenge is to create a long series of unique positions that "look like mate" (though this subjective quality is not an actual requirement) before the final checkmate.
– Mur
Commented Mar 7, 2023 at 0:46
• The requirement of 'unique moves' is a bit mysterious, especially as there already is a requirement of non-repeating positions, which seems to cover the same ground. Are they two separate requirements? Or... ?
– user30536
Commented Mar 7, 2023 at 11:17
• @user30536 Two ways of expressing the same idea, that's all. Commented Mar 7, 2023 at 21:25
• @user30536 yes just one requirement, i'm not really a math guy hence the mystery :)
– Mur
Commented Apr 6, 2023 at 18:09

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