hans: 1. b4 a5 2. Bb2 Na6 3. Bd4 Nc5 4. Nc3 Na4 5. Bc5 Nb6 6. b5 Nh6 7. a4 Nf5 8.
Na2 Nh4 9. Nb4 axb4 10. a5 Rb8 11. a6 Na8 12. a7 Nb6 13. a8=Q Rg8 14. Qa2
Ra8 15. Qe6 Ra3 16. Qg6 hxg6 17. Qb1 Na8 18. Ba7 b6 19. Qb3 Bb7 20. Qd3 Bf3
21. Qf5 gxf5 22. Nh3 Bh5 23. Nf4 Bg6 24. e3 Rh8 25. Bc4 Rh6 26. f3 Bh7 27.
Ng6 Bg8 28. Nh8 Rd6 29. h3 g6 30. Rf1 Bh6 31. Rf2 Bf4 32. Rf1 Bh2 33. f4
Rdd3 34. Rf3 Rac3 35. Rg3 Kf8 36. Rg5 Kg7 37. Rh5 Kf6 38. Rh7 Qc8 39. Rg7
Bh7 40. Rg8 Qa6 41. Rb8 Qa3 42. Rb7 Qb2 43. Bb8 Rb3 44. Rba7 Qd4 45. R7a2
Ra3 46. Rb2 Ra7 47. Rba2 Rb7 48. Ba7 Rb8 49. Rb2 Rg8 50. Rba2 Rg7 51. Bb8
Bg8 52. Rb2 Rh7 53. Rba2 Rh5 54. Rb2 Rg5 55. Rba2 Rg3 56. Rb2 Rf3 57. Rba2
Rf2 58. Rb2 Ra3 59. Rba2 Ra7 60. Rb2 Rb7 61. Ba7 Rb8 62. Rba2 Bh7 63. Ra6
Rg8 64. Bb8 Rg7 65. Ra7 Bg8 66. Rb7 Rh7 67. Ba7 Rh5 68. Rb8 Bh7 69. Rg8 Rg5
70. Rg7 Bg8 71. Rh7 Rg3 72. Rh6 Rgf3 73. Bb3 Kg7 74. Ba4 Kf8 75. Rh7 Ke8
76. Rg7 Bh7 77. Bb8 Kd8 78. Bb3 Kc8 79. Rg8+ Kb7 80. Ba4 Qg7 81. Re8 Bg8
82. Rf8 Bg3 83. O-O-O {50 moves rule} 1/2-1/2 (2012-11-14)
Olaf Jenkner: Warum nicht z.B. 83. Te8 remis?
Was bedeutet das Schlüsselwort unused? (2012-11-14)
Henrik Juel: The castling shows that White never moved his king before; otherwise the position could be reached faster, and the 50 moves rule could not be applied.
The keyword unused seems non-sensical here and should be deleted (2012-11-14)
A.Buchanan: This problem is very interesting. It's orthodox 50M, so that castling does not reset the counter, and the timing works out nicely. But it makes me wonder... suppose we have a problem where it is B32 which was the last reset. Then W83 0-0-0 would prove that the position had already been at 50.0. If 50M convention (which needs to be rewritten because it's a mess) operated like 3Rep, then the game end would have been mandatory after B82. So castling W83 would be illegal. Is this how one would want 50M convention to work? Or should there be a carve-out to say: if you can definitely prove that no-one claimed, then no-one claimed. And should there be a similar carve-out for 3Rep rule? See https://www.thehoppermagazine.com/AA010 (2022-01-20)
A.Buchanan: Personally, I think no carve-outs. The 50M convention should be rewritten as: "A position is considered as a draw if it can be proved that the last 50.0 moves in the proof game combined with the solution did not contain a capture or pawn move. Unless expressly stipulated, this applies only to retro-problems." (2022-01-20)
Thomas Volet: What if the composer intends the retroplay to go beyond 50 non-P and non-capturing moves? (2022-01-20)
A.Buchanan: Hi Thomas - thanks for your question. I think it’s best if we take this offline. I will email you, if that’s ok (2022-01-21)
James Malcom: This is the Volet problem in question: P0008399 In hindsight, it is quite humorous that the 75 move rule was later introduced in the 21st century. (2022-01-21)
Thomas Volet: The question was not directed specifically to P0008399, which is just one of several compositions with the property at issue. (2022-01-22)
A.Buchanan: I've emailed Thomas. My earlier comment should have include checkmate as a third mechanism to zero the count. (2022-01-22)
James Malcom: You can always carry it on over to MatPlus. (2022-01-24)
A.Buchanan: Gah: Thomas sent a short email to me saying he hadn't received anything. I am pretty sure that my email must have ended up in his spam folder, so I re-sent from a different email account, but have heard nothing back. So I have emailed him just now from the second email account, asking him to acknowledge receipt. It just occurs to me now that gmail may be disliking the fact that my email includes a number of urls, relevant to the content. So much "spam" is non-spam these days, that I have an auto-reminder to check my spam folders weekly. Maybe he will read this post? So annoying, I only wanted to spare the readership of PDB from being exposed to theological debate. (2022-01-24, hidden) more ...
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Henrik Juel: Note that in problems castling acts like capture and pawn move with respect to the 50 moves rule. After 949.a6xSb7 there are 4 moves left by [Pa7]; but each camp can shift only KDT, on d1-g1 and b8-e8, respectively, so the triple repetition rule now limits the length of the game. (2004-09-09)
A.Buchanan: In some problems it's certainly the case that the 50-move rule operates incorrectly in this way. Such problems are fine, but obviously wouldn't want to impose this as a standard. Different composers can make different assumptions here (2023-06-20)
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Mario Richter: Das Diagramm ist offensichtlich verdruckt (s. sBBa5a6b7c7). Wie lautet die korrekte Stellung? (2010-01-23)
TBr: Habe die Stellung korrigiert laut Problem 188-189. (2020-03-13)
Henrik Juel: Thanks, Thomas
Black captured [Lf1] on f1 and hxgxfxe
Retracting e4-e3 is illegal as [Ph7] captured [Lc1] on a dark square
Outline of retroplay:
Retract -1.Ta7-a6, sTDT to the left, sKe1-f2, wKg1-h1, sSg3-f1, wKh1-g1, sSg3 to g1, extract sTDT via f1 and f3, sSh3-g1, wTb2 to g1, sD to f1, sKf2 to e8, sDf1 to d8, sLg8 to c8, and finally probably -50... b7-b6 to avoid draw by the 50 move rule (2020-03-13)
Mario Richter: Henrik, I don't think that "-50... b7-b6 to avoid draw by the 50 move rule" is the point of this problem. I think the author's intention was to raise the question what has higher priority: 50-moves-rule or checkmate.
So 1. ... Sxd2 mates, the question is, if the non-capturing non-pawn move 1. ... Sd2 too is checkmate.
Furthermore, I do not like the stipulation: White has no mating move, so the question "#1 (wer?)" doesn't make any sense to me. Imho a better stipulation would be "#1, How many solutions?" (2020-03-26)
Henrik Juel: Thanks for providing a retroplay, Mario
You are probably right about the author intention; I think that Plaksin would argue that 1... Sg3 stops the game immediately, with draw by the 50 move rule
The stipulation may have been translated incorrectly from serbo-kroatian (2020-03-27)
A.Buchanan: I’ve modified the stipulation. What was Plaksin’s published solution? The FIDE rules unfortunately allow for arbiter judgement, something that really only should be needed for tournament guidelines. Today if you work through the cases, it seems to be up to the mating player to decide if he wants to claim a draw before he plays the move. The Laws expect rationality. If the rule would cut in 1 single move later, the mated player definitely does not get a chance to use this rule to escape the obligation to declare there is no flight. The Codex simply says if it’s retro, apply the rule - but scoresheets, clocks, arbiters etc don’t exist for a composition so this is meaningless (2022-07-23)
A.Buchanan: It would be possible to redraft the Codex along the lines of the draw by repetition rule, to clarify that pawn move, capture and checkmate all zero the move count.
However there are two other points of view. One is the historical idea that castling (but not other king/rook moves?) also zeroes the count. Even under the current form of the Laws & Codex, the few problems based on this are currently unsound. They deserve to be better protected by redrafting the Codex and then calling the problems out as based on a clear historical interpretation at the time. As with Dummy Pawn, contemporary composers can still “go back in time” to make compositions based on the old interpretation. (2022-07-23)
A.Buchanan: The second objection is more serious, and is an issue in common with draw by repetition. This is whether a player must claim if possible. If you say “no” then there are longer retro sequences possible. But there are also problems which rely on the answer “yes” for soundness. This is a complicated area, and I don’t have an answer currently, although as always I want to protect the integrity and accessibility of prior art, while also giving a clear set of rules for newcomers to work with (2022-07-23)
A.Buchanan: Another “philosophical” issue is how we regard rules at all. I see them as being mathematical, and want to clear them up so engine developers, computer scientists and mathematicians can fully engage with retro chess.
But I must acknowledge that Tom Volet (who I respect very much) comes from a background of law, where interpretation of words is vital. He sees the vagueness as part of the artistry while I see it as a boring barrier to enjoying the artistry that is elsewhere. (2022-07-23)
A.Buchanan: I would like to explore a clause for both 3Rep and 50M, that claiming is automatic unless you can show that it didn’t happen (e.g. if a move was played, and there’s no shorter history which avoids the issue). I think this can potentially solve everything but it involves a precision that may be anathema to Tom.
Other fine points are whether stalemate and dead position like checkmate also trump 50M. And how about 50M vs 3Rep? And a separate more difficult point as to whether DP role has visibility over 50M & 3Rep.
And these posts summarise my complete understanding of the issues with the 50M rule. (2022-07-23)
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Henrik Juel: Following R: 76.h3xLg4, the resolution could continue with
Retract wKc8 to b5, sLg4 to c8, b7-b6, sSa8 to g8, wSa4 to g1, wKb5 to e1, sLb8 to a5, b6xTc5, wTc5 to d4, sKa1 to b5, a2xTb3xDc4+, etc. (2020-08-13)
Henrik Juel: A little analysis may be in order
Pawns captured all missing men
Kb3 is now confined to the SW corner, but if we retract b3xc4 he is locked in for good, so [Lc8] was captured on g4
Before we retract h3xLg4, sLg4 to c8, and b7-b6, wKf8 must be liberated
The plan for this is: Retract wKg8-f8, sTg1 to f8, sTe7 out, wTf8 out past the sT, wKg8 to e7, sT to h8, wT to e8, and further as per my old comment (2022-01-22)
James Malcom: Corrected SPG: 1. Nh3 e6 2. Nc3 Qg5 3. Rg1 Qe3 4. dxe3 Bb4 5. Qd4 Nc6 6. Bd2 Na5 7. Kd1 Nb3 8.
axb3 Nf6 9. Ra6 Nd5 10. Rb6 axb6 11. Kc1 Ra4 12. Kb1 Ba5 13. Nd1 Rc4 14. Ka1 Ke7
15. Nf4 Kd6 16. Bb4+ Kc6 17. h3 Kb5 18. bxc4+ Ka4 19. c3 Kb3 20. Qc5 Kc2 21. Ka2
bxc5 22. Ka3 Bb6 23. Ka4 Ba7 24. Kb5 Nb6 25. Nd5 Na8 26. Nb6 Re8 27. Na4 b6 28.
Rh1 Bb7 29. Rh2 Bf3 30. Ka6 Bh5 31. Kb7 Re7 32. Kc8 Bg4 33. hxg4 Kb3 34. Rh5 Kc2
35. Rd5 Kb3 36. Rd2 Ka2 37. Rc2 Kb3 38. Rc1 Ka2 39. Ra1+ Kb3 40. Ra3+ Kc2 41.
Rb3 Bb8 42. Ba3 Ba7 43. Rb5 Bb8 44. Ra5 Kb3 45. Ra7 Kc2 46. Rb7 Ba7 47. Rb8 Re8+
48. Kb7 Rg8 49. Rf8 Kd2 50. Kc8 Ke1 51. Kd8 Rh8 52. Ke7 Rg8 53. Rb8 Rc8 54. Rb7
Bb8 55. Ra7 Rd8 56. Ra5 Ba7 57. Rb5 Rb8 58. Rb3 Rb7 59. Bb4 Bb8 60. Ra3 Ra7 61.
Ra1 Ra5 62. Rc1 Rb5 63. Ba5 Rb3 64. Rc2 Ra3 65. Rd2 Ra1 66. Rd6 Rc1 67. Kf8 Rc2
68. Kg8 Rd2 69. Rd5 Rd4 70. Rd6 Re4 71. Rd2 Rd4 72. Rc2 Rd2 73. Rc1 Rc2 74. Ra1
Rc1 75. Ra3 Ra1 76. Rb3 Ra3 77. Rb5 Rb3 78. Bb4 Kd2 79. Ra5 Kc2 80. Ba3 Rb5 81.
Ra7 Ra5 82. Rb7 Ba7 83. Rb8 Kb3 84. Rd8 Bb8 85. Re8 Ra7 86. Kh8 Rb7 87. Rf8 Ba7
88. Re8 Rb8 89. Rf8 Re8 90. Kg8 Re7 91. Rb8 Kc2 92. Rb7 Bb8 93. Ra7 Kb3 94. Ra5
Kc2 95. Rb5 Kb1 96. Rb3 Kc1 97. Bb4 Kb1 98. Ra3 Kc2 99. Ra1 Kb3 100. Rc1 Ba7
101. Rc2 Ka2 102. Rd2 Kb1 103. Rd5 Kc2 104. Rh5 Kc1 105. Rh1 Kb1 106. Rg1 Kc2
107. Ba3 Kb3 108. Kf8 (2023-03-11)
AV: On part de la position Rb5, Th1, Fa3 et f1, Ca4 et d1, Pb2, c3, c4, e2, e3, f2, g2 et h2 (14) / Rb3, Th8, Fa7 et c8, Ca8, Pb7, c5, c7, d7, e6, f7, g7 et h7 (13). Et l'on joue :

1...b6 2.h3 Fb7 3.Fb4 Ff3 4.Fa5! Fh5 5.Ra6 Te8 6.Rb7 Te7 7.Rc8 Fg4 8.hxg4 Début du décompte. 8...Rc2 9.Th5 Rb3 10.Td5 Rc2 11.Td2+ Rb3 12.Tc2 Ra2 13.Tc1 Rb3 14.Ta1 Rc2 15.Ta3 Rc1 16.Tb3 Rc2 17.Tb5 Rc1 18.Fb4 Rc2 19.Ta5 Fb8 20.Ta7 Rb3 21.Tb7 Fa7 22.Tb8 Te8+ 23.Rb7 Tg8 24.Tf8 [24.Te8] 24...Rc2 25.Rc8 Rc1 26.Rd8 Rc2 27.Re7 Rc1 28.Tb8 Rd2! [28...Rb1?! 29.Tb7 Fb8 30.Ta7 Rc2 31.Ta5 Fa7 32.Tb5 Tb8 33.Fa5 Tb7 34.Tb3 Fb8 35.Ta3 perd un coup] 29.Tb7 Fb8 30.Ta7 Re1! 31.Ta5 Fa7 32.Tb5 Tb8 33.Fa5 Tb7 34.Tb3 Fb8 35.Ta3 Ta7 36.Fb4 Ta5 37.Ta1 Tb5 38.Fa5 Tb3 39.Tc1 Ta3 40.Tc2 Ta1 41.Td2 Tc1 42.Td4 Tc2 43.Te4 Td2 44.Tf4 Td5 45.Td4 Td6 46.Td2 Td5 47.Tc2 Td2 48.Tc1 Tc2 49.Ta1 Tc1 50.Ta3 Ta1 51.Tb3 Ta3 52.Tb5 Tb3 53.Fb4 Rd2 54.Fa3 Rc2 55.Ta5 Tb5 56.Ta7 Ta5 57.Tb7 Fa7 58.Tb8 Rb3 59.Td8 Fb8 60.Re8 Ta7 61.Rf8 Tb7 62.Rg8 Fa7 63.Tf8 Tb8 64.Rh8 Te8 65.Rg8 Te7 66.Tb8 Rc2 67.Tb7 Fb8 68.Ta7 Rc1 69.Ta5 Fa7 70.Tb5 Rb1 71.Tb3 Rc2 72.Fb4 Rc1 73.Ta3 Rc2 74.Ta1 Rb3 75.Tc1 Ra2 76.Tc2 Rb3 77.Td2 Ra2 78.Td5 Rb3 79.Th5 Ra2 80.Th1 Rb3 81.Tg1 Ra2 82.Fa3 Rb3 83.Rf8 . Donc 75 coups sans prise, roque ni mouvement de pion. (2005-06-25, hidden)
Henrik Juel: James, please note
a. AV's comment uses french notation, RDTFC for KQRBS (german KDTLS)
b. His play is forward from the given position (wKb5, wRh1, ...), not backwards from diagram position (2020-08-13, hidden)
James Malcom: I'm aware that it is French, Henrik, and thanks for explaining that it is foward play. I found a full solution in the Retro Mailing list, which I have modified to fit PDB requirements-https://pairlist1.pair.net/pipermail/retros/2004-December/001006.html (2020-08-13, hidden)
Henrik Juel: Very good, James
It is so nice to be able to use the animation in retros with a looong retroplay (2020-08-13, hidden)
James Malcom: Done and done, Henrik. (2020-08-14, hidden)
Henrik Juel: Fine, James, but you made a small but crucial error at the end
R: 108... e7-e6?? is illegal, because the tempo is wrong and there is no way to change it:
109.Sa3-b1 Sc4-e3 110.Sb1-a3 Sa5-c4 111.Sa3-b1 Sc6-a5 112.Sb1-a3 Sb8-c6
The initial array has been reached, but White should have made the last retraction
R: 108... Sc4-e3 or any other black retraction works (2020-08-15, hidden)
James Malcom: SPG: 1. Nc3 e6 2. Nf3 Qg5 3. h3 Qe3 4. dxe3 Nc6 5. Qd4 Na5 6. Qb6 Nb3 7. axb3 axb6 8. Bd2 Ra4 9. O-O-O Ke7 10. Ng5 Kd6 11. Be1+ Kc5 12. Rd6 Rc4 13. Nd1 Kb5 14. Rc6 Bb4 15. bxc4+ Ka4 16. Ne4 Ba5 17. Bb4 Nf6 18. c3 Kb3 19. Nc5+ Ka2 20. Kc2 Ka1 21. Kb3 Nd5 22. Ka4 Re8 23. Kb5 Ka2 24. Na4 Ka1 25. Rc5 bxc5 26. Rh2 Nb6 27. Rh1 Na8 28. Rh2 Bb6 29. Rh1 Ba7 30. Rh2 b6 31. Rh1 Bb7 32. Rh2 Bf3 33. Rh1 Bg4 34. Ka6 Re7 35. Kb7 Ka2 36. Kc8 Bb8 37. Kd8 Ka1 (2023-03-09, hidden)
James Malcom: SPG: 1. Nh3 e6 2. Nc3 Qg5 3. Rg1 Qe3 4. dxe3 Bb4 5. Qd4 Nc6 6. Bd2 Na5 7. Kd1 Nb3 8. axb3 Nf6 9. Ra6 Nd5 10. Rb6 axb6 11. Kc1 Ra4 12. Kb1 Ba5 13. Nd1 Rc4 14. Ka1 Ke7 15. Nf4 Kd6 16. Bb4+ Kc6 17. h3 Kb5 18. bxc4+ Ka4 19. c3 Kb3 20. Qc5 Kc2 21. Ka2 bxc5 22. Ka3 Bb6 23. Ka4 Ba7 24. Kb5 Nb6 25. Nd5 Na8 26. Nb6 Re8 27. Na4 b6 28. Rh1 Bb7 29. Rh2 Bf3 30. Ka6 Bh5 31. Kb7 Re7 32. Kc8 Bg4 33. hxg4 Kb3 34. Rh3 Kc2 35. Rh5 Kb3 36. Rd5 Kc2 37. Rd2+ Kb3 38. Rc2 Ka2 39. Rc1 Kb3 40. Ra1 Kc2 41. Ra3 Kb1 42. Rb3 Kc2 43. Ba3 Kb1 44. Rb5 Kc2 45. Ra5 Bb8 46. Ra7 Kd2 47. Rb7 Ba7 48. Rb8 Re8+ 49. Kb7 Rh8 50. Rf8 Rg8 51. Kc8 Rh8 52. Kd8 Rg8 53. Ke7 Rh8 54. Rb8 Rc8 55. Rb7 Bb8 56. Ra7 Ke1 57. Ra5 Ba7 58. Rb5 Rb8 59. Rb3 Rb7 60. Bb4 Bb8 61. Ra3 Ra7 62. Ra1 Ra5 63. Rc1 Rb5 64. Ba5 Rb3 65. Rc2 Ra3 66. Rd2 Ra1 67. Rd5 Rc1 68. Kf8 Rc2 69. Kg8 Rd2 70. Rd6 Rd4 71. Rd5 Re4 72. Rd2 Rd4 73. Rc2 Rd2 74. Rc1 Rc2 75. Ra1 Rc1 76. Ra3 Ra1 77. Rb3 Ra3 78. Rb5 Rb3 79.Bb4 Kd2 80. Ba3 Kc1 81. Ra5 Rb5 82. Ra7 Ra5 83. Rb7 Ba7 84. Rb8 Ra6 85. Rf8 Bb8 86. Kh8 Ra7 87. Re8 Rb7 88. Rd8 Ba7 89. Rc8 Rb8 90. Rf8 Re8 91. Kg8 Re7 92. Rb8 Kc2 93. Rb7 Bb8 94. Ra7 Kb3 95. Kf8 Kc2 96. Ra5 Ba7 97. Rb5 Kb1 98. Rb3 Kc2 99. Bb4 Kb1 100. Ra3 Kc2 101. Ra1 Kb3 102. Rc1 Ka2 103. Rc2 Ka1 104. Rd2 Ka2 105. Rd5 Kb1 106. Rh5 Ka2 107. Rh1 Kb3 108. Rg1 (2023-03-10, hidden) more ...
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Thomas Volet: Problem P0008465 is faulty. (2000-11-27)
James Malcom: What is the author's solution and the cook? (2022-01-21)
Mario Richter: I do not the "official cook", but the following should work:
R: 1. Th1-g1 Kf5-e4 2. Th4-h1 Kg6-f5 3. Td4-h4 Kh6-g6 4. Td1-d4 Kg6-h6 5. Ta1-d1 Kh6-g6 6. Ta3-a1 Kg6-h6 7. Tb3-a3 Kh6-g6 8. Tb5-b3 Kg6-h6 9. Ta5-b5 Kh6-g6 10. Lb8-a7 Kg6-h6 11. Ta7-a5 Kh6-g6 12. Tb7-a7 Kg6-h6 13. La7-b8 Kh6-g6 14. Kg8-f8 Kg6-h6 15. Tb8-b7 Kh6-g6 16. Tf8-b8 Te8-e7 17. Lb8-a7 Tc8-e8 18. La7-b8 Tb8-c8 19. Te8-f8 Tb7-b8 20. Lb8-a7 Ta7-b7 21. Kf8-g8 Ta5-a7 22. Ke7-f8 Tb5-a5 23. Kd8-e7 Tb4-b5 24. Kc8-d8 Th4-b4 25. Kb7-c8 Th5-h4 26. Ka6-b7 Tg5-h5 27. Kb5-a6 Tf5-g5 28. Kc4-b5 Te5-f5 29. Kb3-c4 Te4-e5 30. Ka2-b3 Tb4-e4 31. Kb1-a2 Tb5-b4 32. Te7-e8 Ta5-b5 33. Kc1-b1 Ta7-a5 34. Kd1-c1 Tb7-a7 35. La7-b8 Tb8-b7 36. Ke1-d1 Th8-b8 37. Te8-e7 Kg5-h6 38. Tb8-e8 Tg8-h8 39. Tb7-b8 Th8-g8 40. Lb8-a7 Tg8-h8 41. Ta7-b7 Th8-g8 42. Ta5-a7 Tg8-h8 43. Tb5-a5 Th8-g8 44. Tb4-b5 Tg8-h8 45. Th4-b4 Tf8-g8 46. Th1-h4 Th8-f8 47. h2xLg3 (2022-01-23)
Thomas Volet: Mario, I do appreciate your tactfully lengthy unwind, but this effort at economy is hugely flawed. (2022-01-23)
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A.Buchanan: There's a question whether DP rule has visibility of 3Rep & 50M state. The current consensus among most of the tiny group who might care is that for retros, it does have visibility, but for purely forward problems, it does not. This align with the idea that by default 50M & DP rules apply only to retros (2023-09-06)
A.Buchanan: The old intended interpretation is protected under the Golden Age principle. Suppose we do apply modern rules, codex & clarifications. If Black just played Kb7xRa8, then the alternative leading to mate takes 7.0 moves, so this must have been Black's 5892nd move at the latest. If White just moved, then it was White's 5892nd at latest. So to maximize the length of the game, Black moved last. (2023-09-06) edit (2023-09-06)
A.Buchanan: The old intended interpretation is protected under the Golden Age principle. Suppose we do apply modern rules, codex & clarifications: (1) mate trumps 50M (2) 50M applies as this is retro (3) 75M rule exists but does not apply as this is problem not game (4) DP rule exists (5) DP rule applies as this is retro (6) DP has visibility of 50M state as this is retro. If Black just played Kb7xRa8, then the alternative leading to mate takes 7.0 moves, so this must have been Black's 5892nd move at the latest. If White just played Kg2xRh1, then again need another 7.0 moves for the half-duplex mate, which is at the latest Black's 5898th move, so this would have been White's 5892nd move at the latest. So to maximize the length of the game, Black moved last. (2023-09-06, hidden) more ...
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zunächst mit der 3. ehrenden Erwähnung ausgezeichnet, wegen der NL aber in 'Probleemblad' 09-10/2003 von PR Piet le Grand wieder aberkannt.
TV: Cooked by H. Juel, who found a 49.5 move retraction. (2001-09-21)
James Malcom: What is the author's solution and the cook? (2022-01-21)
Henrik Juel: Thanks for providing the retroplays, Mario (2022-03-22)
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Joost de Heer: Correct solution, wrong reasoning. Castling is impossible because, if black can still castle, the diagram position is draw due to the 50-move rule! The 50 white moves are: 34 by wK (screens on c8 [with careful step on a2 to let bB pass] then g8), 11 by wB6 (to e3 to exchange place with bB then screen on a7), 3 by wR (promotion on h8), 2 by wBa4 (Ba6-b5-a4). (2003-08-31, hidden)
Henrik Juel: This problem was awarded a Special prize in the 2001 retros award, appearing belatedly in 12/2010 p.220-227 (2019-11-17, hidden)
Henrik Juel: C+ Popeye 4.61 (also) (2020-10-09, hidden) more ...
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James Malcom: What is the author's solution? (2022-01-21)
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Korrektur zu 16238 aus Heft 271 (Februar 2015) [Pxxxxxxx]

Autor Tom Volet: "I believe this to be the first published example of a 50 move draw sequence in which the move that immediately precedes the sequence must have been (not could have been), applying only the rules of forward chess without regard to problem conventions or stipulations as to forward play, a capture of a unit by a unit."
Kees: . from PAS

1. Na3 Na6 2. Nb5 Nc5 3. Nd4 Ne6 4. Nb3 Ng5 5. Rb1 Nh3 6. Na1 Nf6 7. gxh3 Nd5 8. Bg2 Nb6 9. Bd5 Rb8 10. a4 Na8 11. Ba2 a6 12. b3 Rg8 13. Ba3 Rh8 14. Bc5 Rg8 15. Ba7 b6 16. Nf3 Bb7 17. Nd4 Bf3 18. Nb5 axb5 19. Qc1 Qc8 20. Qa3 Qb7 21. a5 Qc6 22. Qa4 Kd8 23. Kd1 Kc8 24. Kc1 Kb7 25. Kb2 Re8 26. Rbg1 Kc8 27. Ka3 Kd8 28. Kb4 Qh6 29. Rg6 bxa4 30. Kb5 Rh8 31. Ka6 Bg4 32. Kb7 Bf3+ 33. Rc6 Qg5 34. Kb8 Qg1 35. Rh6 e6 36. Rg6 Bd6 37. Rh6 Reg8 38. Rg6 Bf8 39. Rh6 Ke7 40. Kc8 Kd6 41. Kd8 Kc5 42. Rg6 Be7+ 43. Kxe7 Rb8 44. Rh6 Rb7 45. Bb8 Ra7 46. Rg6 Ra6 47. Ba7 Rb8 48. Rh6 Rb7 49. Kf8 Kd6 50. Kg8 Ke7 51. Kh8 Kf8 52. Rg6 Rb8 53. Rh6 Re8 54. Rg6 Re7 55. Rh6 Ke8 56. Rg6 Kd8 57. Rh6 Kc8 58. Rg6 Kb7 59. Rh6 Kc6 60. Rg6 Kb5 61. Rh6 Kb4 62. Rg6 Ka3 63. Rh6 Kb2 64. Rg6 Kc1 65. Rh6 Kd1 66. Rg6 Ke1 67. Rh6 Kf1 68. Bb8 Kg2 69. Kg8 Qb1 70. Kf8 Qb2 71. Rb1 Qf6 72. Rb2 Kf1 73. Bb1 Ke1 74. Ra2 Kd1 75. Ra3 Kc1 76. Rg6 Kb2 77. Rg1 Qg6 78. Rh1 Qg1 79. Ba7 Kc1 80. Bb8 Kd1 81. Ba7 Ke1 82. Bb8 Kf1 83. Ba7 Kg2 84. Bb8 Qc1 85. Ba2 Qb2 86. Rb1 Qc1 87. Rb2 Kf1 88. Rb1 Bh1 89. Rb2 Kg2 90. Rb1 Qb2 91. Re1 Qc1 92. Bb1 Qd1 93. Ra2 {50 moves rule} Qc1 94. Rb2 Qd1 95. Ba2 Ra7 96. Rb1 Rb7 97. Ba7 Qc1 (2022-03-14)
Thomas Volet: Apologies to Thierry. I should have addressed this earlier. My remark quoted above was (if recollection serves) made along with the submission of the composition for publication. Regardless, my belief at at the time was incorrect as I was then unaware of Nikita Plaksin's mirror compositions P0004364 and P0004395 (published in 1969). Both show the retroplay sequence ending (just short of the draw that the prevailing convention dictated, which saves the stipulated Mate in 3) in the uncapture by a King of a Bishop on the Bishop's home square, from which the Bishop never moved (exit Pawns occupying their home squares in the diagrams). The above 2016 joint composition with Thierry shows the 50 move retroplay sequence of non-Pawn, non-capturing moves being immediately followed by the uncapture by a King of a non-Pawn unit that has moved from its home square. That feature, which presents some additional constraints on realization, may also have been presented before, but obviously I should leave that to better historians. (2022-07-27)
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Editor's comment: Do not be put off by the length of R546: there is a repeated sequence of moves.
James Malcom: Solution? Also, is this an Othoreconstrution? (2023-05-30)
Henrik Juel: Here is the solution from the May 2020 issue (from www.theproblemist.org , which is a treasure of info, althoug I find it hard to navigate)
R546 (Le Gleuher): Retroanalysis: The wPs captured the 4 missing black units.
Thus, wPb4 comes from b2, and (Pa2) promoted to the extra wR on a8 with (Pa7)
letting it pass by switching to the b file (first capture of the 3 missing white units).
(Pb7) must have promoted to a rook on a1 or c1 (second capture). (Ph7) must
have moved onto the g file (third and final capture) in order to be captured. Thus
(Pc7) and (Pe7) promoted to rooks on the c and e files, respectively. It is not
possible to immediately take back a4xb3 or c2xd3. The retro-move e4xf5 is
forbidden since then the bP which promoted on e1 cannot retract to e5. Black can
only move in the southeast cage, while White’s bishop is free to oscillate between
c2 and b1.
Black to move: back 1.Bc2-b1 Kg1-f1 2.Bb1-c2 Rf1-f2 3.Bc2-b1 Rf2-f3
4.Bb1-c2 Rf3-g3 5.Bc2-b1 Rg3-h3 6.Rh3-h2 Rh2-h1 7.Bb1-c2 Kh1-g1 8.Bc2-b1
Rg1-f1 9.Bb1-c2 Rf1-f2 10.Bc2-b1 Rf2-f3 11.Bb1-c2 Rf3-g3 12.Rg3-h3 Rh3-h2
13.Bc2-b1 Kh2-h1 14.Bb1-c2 Rh1-g1 15.Bc2-b1 Kg1-h2 16.Bb1-c2 Rh2-h1
17.Bc2-b1 Kh1-g1 18.Bb1-c2 Rg1-f1 19.Bc2-b1 Rf1-f2 20.Bb1-c2 Rf2-f3
21.Rf3-g3 Rg3-h3 22.Bc2-b1 Rh3-h2 23.Bb1-c2 Kh2-h1 24.Bc2-b1 Rh1-g1
25.Bb1-c2 Kg1-h2 26.Bc2-b1 Rh2-h1 27.Bb1-c2 Kh1-g1 28.Bc2-b1 Rg1-f1
29.Bb1-c2 Rf1-f2 30.Rf2-f3 Rf3-g3 31.Bc2-b1 Rg3-h3 32.Bb1-c2 Rh3-h2
33.Bc2-b1 Kh2-h1 34.Bb1-c2 Rh1-g1 35.Bc2-b1 Rg1-f1 36.Rf1-f2 Bf2-e1
37.Re1-f1 Rf1-g1 38.Bb1-c2 Rg1-h1 39.Bc2-b1 Kh1-h2 40.Bb1-c2 Rh2-h3
41.Bc2-b1 Rh3-g3 42.Bb1-c2 Bg3-f2 43.Bc2-b1 Rf2-f1 44.Bb1-c2 Rf1-g1
45.Bc2-b1 Kg1-h1 46.Bb1-c2 Rh1-h2 47.Bc2-b1 Kh2-g1 48.Bb1-c2 Rg1-h1
49.Bc2-b1 Kh1-h2 50.Bb1-c2 Rh2-h3 51.h3-h4 Bh4-g3 52.Bc2-b1
then 52…Rg3-f3 (or 52...Bg3-h4 53.Bb1-c2 Bh4-g3…) 53.Bb1-c2 Rf3-f2 54.Bc2-b1 Rf2-f1 55.Bb1-c2
Rf1-g1 56.Bc2-b1 Kg1-h1 57.Bb1-c2 Rh1-h2 58.h2-h3 Rh3-g3 59.Bc2-b1 Bg3-h4 60.Bb1-c2 Rh8-h3 etc…
The diagram position is a draw and the last 103 single moves are determined.
White to move: back 1…Kg1-f1 …
51.h3-h4 Bh4-g3 52.Bc2-b1 then the same… Here, there are 99 single moves between the diagram position and the retro-move h3-h4. Of course, trying to insert another manoeuvre in the solution would lead to an overshoot of the 101 single moves, which would be incompatible with the 50 moves rule. Here only 102 last single moves are determined.
So, we have a D25/102, a new record for last single moves for ‘D’ type (Duplex) with 25 pieces (It is also
the overall record for Duplex). With black to move, the same diagram is also a record with 25 pieces (B25/103) (2023-05-30)
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Henrik Juel: 3 and 5 captures by white and black pawns are obvious, leaving [Ph2,Ph7], so the remaining white capture was hxg (with promotions on g8 and h1) or officerxPh (with promotion on h8) (2022-11-05)
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AB: An amazing young composer...
James Malcom: Thanks for adding this in Andrew. I have updated it to include the solution. (2022-01-31)
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