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What is the longest fixed consecutive series of moves for one player such that the other player's response is forced every move? Assume draw rules must be obeyed (threefold repetition, 50-move rule, etc.).

Note that the moves are only forced for the opponent or 'forced' player; for the forcing player, there is no requirement their moves be forced (as in Longest sequence of mutually forced moves). The forcing player's moves need only be a fixed predetermined sequence to which every response of the opponent is forced.

The sequence ends when a) the forced player plays their final forced response, such that whatever the forcing player does next move, the forced player will have a choice of multiple replies; or b) the game terminates (checkmate, stalemate, draw by threefold repetition, draw by 50-move rule, etc.).

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The longest sequence I have created is 3648.5 moves long, abusing the 50-move rule to its fullest. Throughout the entire sequence, Black has only one legal move as stipulated. I can guarantee that threefold repetition is avoided all the way through. It is a very simple trick of committing to using king, knight, and bishop moves all around the board.

Firstly, we start with this position. The first step is to use up all of Black's pawn moves. Black has 11 pawn moves that can be made before they all must be captured. Each capture adds on 49.5 moves due to parity. This gives us a total of (11x50)+(49.5x3)=698.5 moves to start with.

Here is a demonstration without all of the interim moves. This shows why this calculation is made as it is.

[FEN "5BNk/p1p1pB2/Q1R1Rp2/5K2/8/P6P/P1PPPP1P/6N1 w - - 0 1"]

1. Nf3 Kh7 2. Nh4 Kh8 3. Ng6+ Kh7 4. Kf4 f5 5. Nh4 Kh8 6. Ng6+ Kh7 7. Kf3 f4 8. Nh4 Kh8 9. Kxf4 Kh7 10. Kg3 Kh8 11. Ng6+ Kh7 12. Re5 e6 13. Nh4 Kh8 14. Ng6+ Kh7 15. Re4 e5 16. Nh4 Kh8 17. Ng6+ Kh7 18. Re3 e4 19. Nh4 Kh8 20. Rxe4 Kh7 21. Re3 Kh8 22. Ng6+ Kh7 23. Rc5 c6 24. Nh4 Kh8 25. Ng6+ Kh7 26. Rc4 c5 27. Nh4 Kh8 28. Ng6+ Kh7 29. Rcc3 c4 30. Nh4 Kh8 31. Rxc4 Kh7 32. Rcc3 Kh8 33. Ng6+ Kh7 34. Qa5 a6 35. Nh4 Kh8 36. Ng6+ Kh7 37. Qa4 a5 38. Nh4 Kh8 39. Ng6+ Kh7 40. Qb5 a4 41. Nh4 Kh8 42. Qxa4

Now White can go crazy with promotion and sacking their pieces. With the pawns on the a to e files, White has 29 available moves. Excluding the king, queen, light-squared bishop, and f to h file pawns, White has 10 pieces to sack. This makes for a total of 698.5+((29+10)x50)=2648.5 moves.

All of these moves can be seen without all of the interim waiting.

[FEN "5BN1/5B1k/8/8/Q6N/P1R1R1KP/P1PPPP1P/8 w - - 0 1"]

1. Qg4 Kh8 2. Qg5 Kh7 3. a4 Kh8 4. a5 Kh7 5. a6 Kh8 6. a7 Kh7 7. a8=Q Kh8 8. Qa6 Kh7 9. Qag6+ Kh8 10. Qh7+ Kxh7 11. a3 Kh8 12. a4 Kh7 13. a5 Kh8 14. a6 Kh7 15. a7 Kh8 16. a8=Q Kh7 17. Qe4+ Kh8 18. Qh7+ Kxh7 19. Rc6 Kh8 20. Bg7+ Kh7 21. Bh8 Kxh8 22. Ne7 Kh7 23. Nd5 Kh8 24. Rg6 Kh7 25. Rg7+ Kh8 26. Rh7+ Kxh7 27. Nf6+ Kh8 28. Nh7 Kxh7 29. c3 Kh8 30. c4 Kh7 31. c5 Kh8 32. c6 Kh7 33. c7 Kh8 34. c8=Q+ Kh7 35. Qcf5+ Kh8 36. Qh7+ Kxh7 37. d3 Kh8 38. d4 Kh7 39. d5 Kh8 40. d6 Kh7 41. d7 Kh8 42. d8=Q+ Kh7 43. Qd3+ Kh8 44. Qh7+ Kxh7 45. Re6 Kh8 46. Rg6 Kh7 47. Rg7+ Kh8 48. Rh7+ Kxh7 49. Nf5 Kh8 50. Ne7 Kh7 51. Nd5 Kh8 52. e3 Kh7 53. Nf6+ Kh8 54. Nh7 Kxh7 55. e4 Kh8 56. e5 Kh7 57. e6 Kh8 58. e7 Kh7 59. Kf4 Kh8 60. e8=Q+ Kh7 61. Qe4+ Kh8 62. Qh7+ Kxh7

Next, White shifts the Black king to the other side of the board. Now the remaining pieces, minus the queen, may be sacked. In total, this allows for 17 more pawn moves and one piece to sack. This brings the total to ((2+17)x50)+2648.5=3598.5.

[FEN "8/5B1k/8/6Q1/5K2/7P/5P1P/8 w - - 0 1"]

1. Kf5 Kh8 2. Kf6 Kh7 3. Bh5 Kh8 4. Bg4 Kh7 5. Qh5+ Kg8 6. Be2 Kf8 7. Qh7 Ke8 8. Qg7 Kd8 9. Qf7 Kc8 10. Qe7 Kb8 11. Qd7 Ka8 12. Bb5 Kb8 13. Ke6 Ka8 14. Bc6+ Kb8 15. Ba8 Kxa8 16. f3 Kb8 17. f4 Ka8 18. f5 Kb8 19. f6 Ka8 20. f7 Kb8 21. f8=B Ka8 22. Be7 Kb8 23. Bd6+ Ka8 24. Bb8 Kxb8 25. h4 Ka8 26. h5 Kb8 27. h6 Ka8 28. h7 Kb8 29. h8=B Ka8 30. Bg7 Kb8 31. Be5+ Ka8 32. Bb8 Kxb8 33. h3 Ka8 34. h4 Kb8 35. h5 Ka8 36. h6 Kb8 37. h7 Ka8 38. h8=B Kb8 39. Be5+ Ka8 40. Bb8 Kxb8

Lastly, White shuffles their king around for 50 moves. The game will automatically end as a draw for a total of 3598.5+50=3648.5 moves. This is the only way to ensure that extra last play that checkmate, stalemate, or a dead position all deny.

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