How to have a position checked?

[peter]

I will try to go back myself and see which is the losing move.

Did let Stockfish run a 3'/move- Backward started at move 35:

[pgn][Event "corr AUT/C34 (AUT)"]
[Site "ICCF"]
[Date "2020.09.01"]
[Round "?"]
[White "Spiegel, Wilfried"]
[Black "Loeschnauer, Ruediger"]
[Result "1-0"]
[ECO "C16"]
[WhiteElo "2432"]
[BlackElo "2448"]
[Annotator "SF20241012"]
[PlyCount "99"]
[EventDate "2020.??.??"]
[EventType "tourn (corr)"]
[SourceTitle "Fernschach2025"]
[SourceDate "2024.10.15"]
[SourceVersion "1"]
[SourceVersionDate "2024.10.15"]
[SourceQuality "1"]

1. e4 {-0.01/46} ({-0.01 Stockfish dev-20241012-9766db81:} 1. Nf3 d5 2. g3 g6 3. d4 Bg7 4. Bg2 Nf6 5. c4 c6 6. cxd5 cxd5 7. Nc3 Nc6 8. Ne5 Bf5 9. O-O O-O 10. Nxc6 bxc6 11. Bf4 Nh5 12. Be3 Nf6 {0.00/50}) 1... e6 {0.05/53} ({Stockfish dev-20241012-9766db81:} 1... e5 2. Nf3 Nc6 3. Bc4 Bc5 4. d3 Nf6 5. c3 O-O 6. O-O d6 7. Re1 a6 8. h3 Ba7 9. Nbd2 Na5 10. a4 Nxc4 11. Nxc4 Re8 12. Be3 Bxe3 13. Nxe3 b6 14. b4 d5 15. a5 Bb7 16. Nd2 b5 17. Ng4 Nxg4 18. Qxg4 d4 19. Qf3 dxc3 20. Nb3 {-0.01/46}) 2. d4 {0.02/52} d5 {0.12/47} 3. Nc3 {0.13/57} Bb4 {0.35/44} ({Stockfish dev-20241012-9766db81:} 3... Nf6 4. e5 Nfd7 5. f4 c5 6. Nf3 Nc6 7. Be3 cxd4 8. Nxd4 Qb6 9. Qd2 Qxb2 10. Rb1 Qa3 11. Bb5 Nxd4 12. Bxd4 a6 13. Bxd7+ Bxd7 14. Rb3 Qe7 15. Rxb7 Qd8 16. O-O Qc8 17. Rb3 Bc5 18. Rf2 Qc6 19. Ne2 O-O 20. g4 f6 21. exf6 Rxf6 22. Qe3 Rc8 23. g5 Rf7 24. h4 Bd6 25. Rb6 Qc7 26. h5 Rcf8 27. g6 hxg6 28. hxg6 Rf6 29. f5 e5 30. Rxd6 Rxd6 31. Bxe5 Rxf5 32. Bxd6 Qxd6 33. Rxf5 Bxf5 34. Qe8+ Qf8 35. Qc6 Qc8 36. Qxd5+ Be6 37. Qe5 Bf5 38. Qd6 Be4 {0.13/57}) 4. e5 {0.30/48} Ne7 {0.34/47} 5. a3 {0.36/46} Bxc3+ {0.43/41} 6. bxc3 {0.45/44} b6 {0.93/51} ({Stockfish dev-20241012-9766db81:} 6... c5 7. Qg4 cxd4 8. Qxg7 Rg8 9. Qxh7 Qc7 10. Qd3 Qxe5+ 11. Ne2 dxc3 12. Qxc3 Qxc3+ 13. Nxc3 e5 14. h4 Be6 15. Rb1 b6 16. h5 Nbc6 17. f4 f6 18. fxe5 Nxe5 19. Nb5 Kd7 20. h6 Nf5 21. h7 Rh8 22. Bf4 Ng6 23. Rb4 a5 24. Ra4 Nfh4 25. g3 {0.45/44}) 7. Qg4 {0.93/50} Ng6 {1.03/48} 8. h4 {1.00/53} h5 {1.01/52} 9. Qd1 {0.68/42} ({Stockfish dev-20241012-9766db81:} 9. Qg3 Ba6 10. Bxa6 Nxa6 11. Bg5 Qd7 12. Ne2 Nb8 13. Qf3 Qc6 14. O-O Nd7 15. Qg3 Rg8 16. Qd3 Qc4 17. Qe3 Ngf8 18. Nf4 Nh7 19. Nh3 Ndf8 20. Rab1 a5 21. g3 Nd7 22. Rbd1 Nxg5 23. Nxg5 g6 24. Rd3 Rg7 25. Qf4 O-O-O 26. Rf3 Re8 27. Qd2 Re7 28. Nh3 Rh7 29. Qg5 Re8 30. Re1 Nb8 31. Qf4 Nd7 32. Ra1 Re7 33. Ng5 {1.01/52}) 9... Qd7 {1.40/44} ({Stockfish dev-20241012-9766db81:} 9... c5 10. a4 Qc7 11. Bg5 a5 12. Be2 Ba6 13. Bxa6 Nxa6 14. Ne2 Rc8 15. Rc1 Nb8 16. O-O Nd7 17. f4 O-O 18. Ng3 cxd4 19. cxd4 f6 20. Qxh5 Qc3 21. Kh2 Ne7 22. Qg4 Qc6 23. Nh5 fxg5 24. Qxg5 Rf7 25. f5 Nf8 26. fxe6 Nxe6 27. Qg4 g6 28. c3 Rxf1 29. Rxf1 Rf8 30. Nf6+ Kg7 31. h5 Rh8 32. Kg1 Rh6 33. Qf3 gxh5 34. Nxh5+ Kh8 35. Qg4 Qe8 36. Nf6 Qf7 37. Rf3 Ng8 38. Rh3 Rxh3 39. Qxh3+ Kg7 40. Qh7+ Kf8 41. Qxf7+ Kxf7 42. Nxd5 Ng5 43. Kf2 {0.68/42}) 10. Be2 {1.31/49} Ba6 {1.36/44} 11. Bxh5 {1.29/51} Qb5 {1.32/39} 12. Be2 {1.27/51} Qa5 {1.34/49} 13. Bxa6 {1.18/47} Nxa6 {1.32/42} 14. Bg5 {1.26/46} Qxc3+ {1.26/44} 15. Kf1 {1.29/47} c5 {1.33/41} 16. Ne2 {1.22/43} Qc4 {1.25/43} 17. c3 {1.14/45} Nb8 {1.11/46} 18. Kg1 {1.17/53} Nc6 {1.20/51} 19. h5 {1.22/50} Nge7 {1.25/48} 20. Rh3 {1.22/47} Rc8 {1.13/42} 21. Qd2 {1.14/45} Qb3 {1.66/38} ({Stockfish dev-20241012-9766db81:} 21... Kd7 22. Rc1 Rh7 23. Rd1 Rhh8 24. Ng3 cxd4 25. cxd4 Qa4 26. Ne2 Nf5 27. Kh2 Na5 28. g4 Nc4 29. Qe1 Nh6 30. Bxh6 Rxh6 31. Rdd3 Kc7 32. Rdf3 Qe8 33. g5 Rh8 34. Nf4 Kb7 35. Kg2 Rc7 36. Qd1 Na5 37. Qd2 Qg8 38. Ne2 Qh7 39. Rxf7 Rxf7 40. g6 Qg8 41. gxf7 Qxf7 42. Qf4 Qd7 43. Qf3 Nc6 44. Rg3 Rh7 45. Rg6 Rh6 46. Qf8 Rxg6+ 47. hxg6 {1.14/45}) 22. a4 {1.54/42} Nf5 {1.88/38} ({Stockfish dev-20241012-9766db81:} 22... Qc4 23. g4 Rc7 24. Kg2 Rh7 25. Rf1 Ng8 26. f4 f6 27. Bh4 f5 28. gxf5 exf5 29. Bg5 Nge7 30. Ra1 Nd8 31. a5 b5 32. dxc5 Ne6 33. Nd4 Nxc5 34. Bxe7 Ne4 35. Qa2 Kxe7 36. Nxf5+ Kf7 37. Qc2 Kg8 38. Re1 Rf7 39. Nd6 Nxd6 40. exd6 Rf8 41. Qg6 Qxf4 {1.54/42}) 23. a5 {1.73/45} bxa5 {1.93/40} 24. g4 {1.88/50} Nh6 {1.77/47} 25. Rg3 {1.62/50} Qc4 {1.93/39} 26. Qd1 {1.79/47} Ng8 {2.20/37} ({Stockfish dev-20241012-9766db81:} 26... a6 27. Bc1 Rb8 28. Ba3 O-O 29. Bxc5 Rfc8 30. Ba3 Qb3 31. Qd3 Qa4 32. Kg2 Rb3 33. Qxa6 Rcb8 34. Bb2 Qb5 35. Qxb5 R3xb5 36. Bc1 Rb1 37. Ra2 Ra8 38. Kh3 a4 39. Rg1 Rb3 40. Ba3 Na7 41. Rga1 Nb5 42. Bb4 a3 43. Nc1 Rb2 44. Nd3 Rxa2 45. Rxa2 Rc8 46. Nc5 Kh7 47. f3 Rc7 48. Ra1 Ra7 49. Nd3 Rb7 50. Bxa3 Nxc3 51. Bc5 Ne2 52. Nc1 Nxc1 53. Rxc1 Rb3 54. Kg3 g6 55. Rh1 gxh5 56. Rxh5 Kg6 57. Bf8 Nf5+ 58. Kf4 f6 59. exf6 Nxd4 60. Rh6+ Kf7 61. Bc5 Nxf3 62. g5 e5+ 63. Kf5 Nxg5 64. Kxg5 Ke6 65. Bf2 Rf3 66. Bh4 Rf4 67. Kg6 {1.79/47}) 27. dxc5 {1.97/44} Qxc5 {2.64/33} ({Stockfish dev-20241012-9766db81:} 27... Nge7 28. Nd4 Nxd4 29. cxd4 Nc6 30. Ra4 Qa6 31. Kg2 Rb8 32. Bd2 Rb5 33. Rga3 Rb2 34. Bxa5 Qb5 35. Qd3 Qxd3 36. Rxd3 O-O 37. Bd2 Rb1 38. Ra6 Rc8 39. Bc3 g6 40. hxg6 fxg6 41. Rh3 Rb3 42. Ra1 Re8 43. Rah1 Kf8 44. Rh8+ Ke7 45. R8h7+ Kd8 46. Bd2 Kc8 47. Rg7 Rb7 48. Rxg6 Nxd4 49. Rf6 Kd7 50. Rhh6 a5 51. Bxa5 Kc6 52. Bd2 Rbe7 53. Rf4 Nb5 54. g5 {1.97/44}) 28. Nd4 {2.55/42} Nge7 {2.68/35} 29. Rb1 {2.53/42} Rb8 {2.70/35} 30. Rxb8+ {2.53/41} Nxb8 {2.60/37} 31. Qa4+ {2.43/43} Nd7 {2.70/36} 32. Re3 {2.58/41} Qb6 (32... Nc8 {2.80/36 Output SF 241012} 33. Nf5 {2.65/37 224} Rh7 {2.80/38} (33... Rg8 {2.10/37 182 Lc0-SF from 32...Nc8} 34. Nd4 {2.05/21 0} Ncb6 {2.45/41 751} 35. Qc2 {2.27/21 0} Nf8 {2.58/29 40} 36. Re1 {2.29/19 0} Qc4 {2.69/38 331} 37. Kg2 {2.38/19 1} Kd7 {2.89/41 268 (Th8)} 38. Be3 {2.54/17 161} Ke8 {2.83/35 0} 39. f3 {3.21/20 294} Rh8 {3.15/34 0} 40. Qb1 {3.43/21 2 (Lg5)} Nfd7 {3.44/32 105} 41. Nxe6 {3.79/22 78} fxe6 {3.81/30 0} 42. Qg6+ {3.65/21 25} Kd8 {3.79/28 0} 43. Qxg7 {3.43/20 76} Re8 {3.99/32 0} 44. h6 {3.28/19 34 (Df7)} Nf8 {3.15/24 10} 45. h7 {3.25/18 53} Nxh7 {3.56/31 0} 46. Qxh7 {3.15/17 28} Qc7 {3.59/27 3} 47. Qg6 {3.19/15 31} Qc6 {3.93/31 5 (Kd7)} 48. Rh1 {3.78/14 141} a4 {4.29/34 0} 49. Rh7 {4.20/15 50} d4 {4.53/30 0} 50. cxd4 {4.45/15 118} Kc8 {4.78/35 0} 51. Rxa7 {5.01/15 47} Kb8 {4.91/31 0 (Tf8)} 52. Ra5 {6.25/14 65 (Ta6)} Rf8 {4.19/25 11} 53. d5 {6.29/15 32} Nxd5 {4.47/29 14} 54. Ba7+ {7.12/15 55 (Db1+)} Kc8 {8.25/32 41} 55. Qh6 {8.01/15 2} Qe8 {9.02/28 9 (Sf4+)} 56. Bc5 {11.80/10 66} Rg8 {9.46/33 0 (Th8)} 57. Bd6 {13.93/10 54 (Ta8+)} Rh8 {#17/43 8 (Dd7)} 58. Qg7 {18.25/10 24} Ne7 {199.80/67 0} 59. Bxe7 {19.84/10 25 (Ta8+)} Rg8 {#14/62 3} 60. Qf6 {31.79/9 19 (Dxg8)} Qg6 {199.61/30 4} 61. Qf4 {21.79/8 18 (Dxg6)} Qd3 {#12/70 8 (Dc2+)} 62. Kg3 {27.04/8 20} Qc3 {#11/78 0} 63. Bb4 {35.68/7 9 (Tc5+)} Qc6 {#11/72 5} 64. Rc5 {39.01/7 18} Qxc5 {#10/92 0} 65. Bxc5 {63.10/7 5} Rd8 {#9/94 1 (Tg7)} 66. Qxa4 {39.18/6 18} Kc7 {#8/108 0} 67. Qa6 {69.03/6 9 (Db5)} Rd1 {#7/128 6 (Td3)} 68. Bd6+ {#111/1 0} Rxd6 {#6/245 0} 69. Qxd6+ {#110/1 0} Kc8 {#5/245 0 (Kb7)} 70. Qxe6+ {#108/1 0 (g5)} Kb8 {1/0 0} 71. g5 {1/0 0} Kc7 {1/0 0} 72. f4 {1/0 0} Kb8 {1/0 0} 73. g6 {1/0 0} Ka8 {1/0 0} 74. f5 {1/0 0} Kb8 {1/0 0} 75. f6 {1/0 0} Kb7 {1/0 0} 76. f7 {1/0 0} Ka7 {1/0 0} 77. f8=Q {1/0 0} Kb7 {1/1 0} 78. g7 {1/1 0} Ka7 {1/0 0} 79. g8=Q {1/0 0} Kb7 {1/1 0} 80. Qfe7# {#1/0 0;1-0 Lc0 v0.31.2-Stockfish AMD, Schnellschach 25.0min+5.0sek (1)}) 34. Nd4 {2.64/39} Ncb6 {2.79/34} 35. Qc2 {2.53/39} Nf8 {2.35/34}) 33. f4 Ng8 (33... g6 {Output SF 241012 at 32...} 34. h6 Ng8 35. Qa3 Qc5 {3.07/40}) 34. Qa3 Qc5 35. Qxc5 Nxc5 36. c4 dxc4 37. Rc3 Ne4 38. Rxc4 Kd7 39. Nb5 Nxg5 40. fxg5 a6 41. Rd4+ Kc6 42. Nd6 Ne7 43. Nxf7 Rg8 44. Rc4+ Kd5 45. Ra4 Nc6 46. h6 gxh6 47. gxh6 Nd4 48. Rxa5+ Ke4 49. h7 Rxg4+ 50. Kf2 1-0
[/pgn]

The game Lc0- SF is pasted too, regards

[fishpov]

some people here say that's not a 'proof' (*);
expecting that maybe magically after 20 hrs of analysis or so the eval would
suddenly drop back to zero (the latter can happen if there is eg. +1.5 eval
with eg opposite bishops but then the eval wouldn't be increasing after 2 hrs).

Could you give me an example ?
I think when evaluation after long time doesn't increase you're right but if eval increases more and more I have never found example where eval suddenly drop back.

[jefk]

example ?
First, my comment was meant in an ironic sense.
Indeed it (sudden decrease) usually doesn't happen.

But i can think of artificial problems like b or w plays (with disadvantage)
and draws. A tactical problem, whereby b or w with some tricks can
force a draw (against apparent overwhelming better opponent position).

Such tactical problems usually don't occur in normal games (unless it's a Tal game or so;
but then it anyway can be avoided with other earlier moves).