A game leading to a given position is called a proof game. Of course any proof game can be prepended with 1.Nf3 Nf6 2.Ng1 Ng8, so we defined a shortest proof game as, duh, the shortest possible proof game. Especially interesting are unique shortest proof games. For example, 1.e4 e5 2.Nf3 is not unique - White could swap moves. In contrast, 1.e4 e5 2.Bc4 is unique.

Rules of the fun game: First one creating a position without a unique shortest proof game loses. And that's it.

Do you have ideas for strategies or even a forced win for one side? Checking might be a good idea to force the hand of the opponent; 1.e4 d5?! 2.Bb5+ and now Nc6 or c6 lose, but anything to d7 is OK. (EDIT: And don't let your opponent capture, since one-side noncommuting moves run out quite fast.)

(For testers: Proof game checkers exist.)

  • 1
    Can you also lose by being checkmated? Oct 23, 2022 at 1:03
  • @NoamD.Elkies: The problem forum where I found this game said nothing about that. I think any move ending the game (stalemate, 50 move rule, etc.) should be treated as an attempt to bail out :-) and thus lose. Oct 23, 2022 at 8:15
  • 2
    @MiguelAmbrona Why not? Prepending 1 Nf3 Nh6 2 Ng1 Ng8 doesn't lose any castling rights. Oct 23, 2022 at 21:45
  • 1
    @supercat: You can do a PDB search by going on pdb.dieschwalbe.de/index.jsp and enter K='unique proof game' AND SOL='#'. This is no surefire answer, as '#' might be omitted and not all UPGs are in the database. A fleeting search gave the P0002187 with whopping 38.5 moves! (418 games are shown, so even that might not be the record...) Oct 25, 2022 at 7:45
  • 1
    @NoamD.Elkies (and HaukeReddmann): If the rules are that checkmate has the same result as in ordinary chess, then one interesting result is that 1. f3 is a losing move for white. Black has a couple losing moves, but the best response of e5 forces Kf2 and black can continue so that the whole game is forced as follows: 1. f3? e5 2. Kf2 Qh4+ 3. Ke3 Qd4#!
    – A. Rex
    Oct 27, 2022 at 1:16


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.