You can't get there from here...

[KLc]

Hello:

How could I be so blind to not queen the pawn in my solution? Thank you Uri for finishing the job.

I tried Natch 3.3 (64-bit Windows) to get the shortest proof game (or one of them if there are more with the same number of moves) but it seems unfeasible for me. Setting 2 GB of hash in my system, I get the following solution times (or lack of solutions):

Code: Select all

Plies   Time (s)   Solutions found
  28       0.00           0
  29       0.46           0
  30       1.23           0
  31       1.37           0
  32       3.32           0
  33       3.95           0
  34       9.73           0
  35      29.10           0
  36      71.61           0
  37      71.78           0
  38     170.43           0

Uri's solution has got 57 full moves = 114 plies. OTOH, we finally found that you could get there from here!

Regards from Spain.

Ajedrecista.

I never had any luck with Natch. The thing is also that it only looks for solutions with a prescribed number of moves. On the one hand this reduces the size of the solution space but I feel that hitting that space is also harder. I wonder if there’s any approach trying to just find some solution, even if it’s a ridiculous number of moves.

[Dann Corbit]

None of the programs I tried can do what I want, which is to back up arbitrarily (1 ply to k plies) possibly all the way to the game start.

However, I have source code for two of them, and I might try to use some of their guts to make something that does what I want.

[Ajedrecista]

Hello:

I found the basis for a shorter proof game by chance!

The Kuwait Immortal (John Tromp's page).

The Kuwait Immortal (Tim Krabbé's page).

I took the position after 34.- bxa7+ and after some blindfold attempts I arrived to the position of the OP of this thread in 37 moves (20 moves less than the previous best attempt), which I think there is not any shorter proof game after 34.- bxa7+. There are multiple solutions from 34.- bxa7+, so I post only one in the PGN below:

[pgn][Event "?"]
[Site "?"]
[Date "?"]
[Round "?"]
[White "?"]
[Black "?"]
[Result "*"]
[ECO "?"]
[Annotator "?"]
[PlyCount "73"]
[EventDate "?"]
[TimeControl "?"]
1. Nh3 f5 2. Na3 h5 3. g4 hxg4 4. Nf4 Rh3 5. Nc4 Ra3
6. bxa3 e5 7. Bb2 d5 8. Bd4 Bd7 9. h4 Bb4 10. h5 Ba4
11. h6 g3 12. h7 g2 13. h8=B g1=R 14. Rh3 g5 15. Rc3 Rg3
16. Bg2 exd4 17. Be4 dxc3 18. Bd4 gxf4 19. Be3 fxe3 20. dxc3 fxe4
21. Qd3 exd3 22. fxe3 dxc4 23. exd3 c5 24. dxc4 b5 25. cxb4 Qa5
26. cxb5 Na6 27. bxa5 O-O-O 28. bxa6 Rd4 29. exd4 Rb3 30. cxb3 Ne7
31. bxa4 Nd5 32. dxc5 Nb6 33. cxb6 Kb8 34. bxa7+ Kc7 35. Rb1 Kc6
36. Rb8 Kd7 37. Re8+ Kxe8 *[/pgn]

Regards from Spain.

Ajedrecista.