Weird position from CSS forum

[Jouni]

[d]RNBKQBNR/PPPPPPPP/8/8/8/8/pppppppp/rnbkqbnr w - - 0 1

Analysis by Stockfish 17:

1.Nf6 Nc3 2.Ng4 Nd5 3.g8Q b1Q 4.Nc6 Nf3 5.b8Q Ba3 6.Bg7 g1Q 7.Bxa1 Qxa1 8.f8Q Nd4 9.Nxd4 Qxd4 10.Qxd5 Qxd5 11.Ne3+ Kc1 12.Nxd5 a1Q 13.Nf4 Bxe7+ 14.Qexe7 Qg3 15.Qb5 Qgc3 16.Bb7 Qxh8 17.Bxh1 Bg2 18.Nxe2+ Kd1 19.Bxg2 Qxf8+ 20.Qxf8 Qxe2 21.Qxe2+ Kxe2
+- (7.49) Depth: 30/62 00:00:35 132mN, tb=9

Analysis by Lc0 v0.31.0:

1.Na6 Na3 2.b8Q b1Q 3.Bb7 Bb2 4.c8Q c1Q 5.Qd6 Qc4 6.Qcc6 Qxc6 7.Bxc6 Qf5 8.Rb8 Qa5+ 9.Qc7 Qxa6 10.Rb6 Qc4 11.a8Q Rc1 12.Rxb2 a1Q 13.Ba4+
= (0.16) Depth: 11/30 00:02:41 97kN

Is this position possible?

[Brunetti]

Is this position possible?

No, pawns cannot pass each other without capturing.

Alex

[Ajedrecista]

Hello Jouni:

Is this position possible?

No, pawns cannot pass each other without capturing.

Alex

I agree with Alex. Looking into a simpler position, with knights exchanged from the initial position:

[d]rNbqkbNr/pppppppp/8/8/8/8/PPPPPPPP/RnBQKBnR w - -

Castlings are possible, despite not having written the castling flags in the FEN string. Natch 3.3 says that it can not be done in less than 20 plies = 10 moves:

rSbqkbSr/pppppppp/8/8/8/8/PPPPPPPP/RsBQKBsR
20 single moves

Code: Select all

.\Natch-3.3>Natch --hash-size 16 --language e --output Solutions.txt Problem.txt
Solutions found: 26498
Positions analysed: 4
Resolution time: 0.26 s.

With 26,498 solutions found (26,498 = 2 × 13,249 just for the record, only a product of two primes). Here is the first SPG (shortest proof game) printed by Natch:

[pgn][Event ""]
[Site ""]
[White ""]
[Black ""]
[PlyCount "20"]
[Result "*"]

1.Na3 Na6 2.Nc4 Nb4 3.Na5 Nd5 4.Nc6 Nc3 5.Nb8 Nb1 6.Nf3 Nf6 7.Nd4 Ne4 8.Nf5 Ng5 9.Nh6 Nh3 10.Ng8 Ng1 *[/pgn]

These solutions do not care if white king's knight ends on g8 or b8, the same with the other knights. The one that I post luckily does, but not all of them. Please take a look to a made-up example where white knights end on their initial side (queenside or kingside), but not the black knights:

[pgn][Event ""]
[Site ""]
[White ""]
[Black ""]
[PlyCount "20"]
[Result "*"]

1.Nc3 Nc6 2.Ne4 Ne5 3.Nc5 Ng6 4.Na6 Nf4 5.Nf3 Nh3 6.Nb8 Ng1 7.Nd4 Nf6 8.Nf5 Ne4 9.Nh6 Nc3 10.Ng8 Nb1 *[/pgn]

Please note that the knights ending in the queenside can enter via a3, a6, c3 or c6; but the knights ending in the kingside can enter only via h3 and h6 because f3 and f6 are forbidden due to checks.

Regards from Spain.

Ajedrecista.