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What is the longest known sequence of moves with upto 6 pieces where each move of both sides is the only move drawing the game (any other move would lose the game) ?

There should not occur any repitition of a position.

I experimented with the endgame rook vs two (three) pawns and got some sequences I unfortunately do not remember.

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  • I truly wish (but doubt) that this is true of the starting position.
    – DongKy
    Jun 27, 2020 at 0:24
  • The starting position may well be a draw, but I highly doubt that all starting moves but one are a forced win for Black :)
    – D M
    Jun 27, 2020 at 14:57

3 Answers 3

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To get the ball rolling, from the following position the first 6 moves for each side are forced in order not to lose. (If 7.h8=B weren't available and 7.h8=Q needed to be played, then the forced follow-ups 7...h1=Q+ 8.Qxa1+ Kxa1 would extend it to 8, but no cigar.)

[FEN "K5R1/8/p7/8/8/7P/8/1q1k4 w - - 0 1"]

1.Rg1+ $1 Kc2 $1 2.Rxb1 $1 Kxb1 $1 3.h4 $1 a5 $1 4.h5 $1 a4 $1 5.h6 $1 a3 
$1 6.h7 $1 a2 $1 7.h8=Q 
    ( 7.h8=B )
7...a1=Q+ $1 8.Qxa1+ $1 Kxa1 $1 *
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  • 2
    already pretty good!
    – Peter
    Mar 11, 2015 at 23:17
  • Don't you get half a cigar if you replace the BPa6 by a bPd6 ? Then 7.h8Q and 7...d1Q are forced too.
    – Evargalo
    May 29 at 15:44
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In the Matplus.net forums, Arpad Rusz shared the longest such sequence in a 6-piece position. The length of it is 19 plies.

You can check the uniqueness for yourself by using the Sygyzy tablebases..

[FEN "3k4/8/8/p4pP1/3K3P/8/8/8 w - - 0 1"]

1. h5 Ke7 2. h6 Kf7 3. Ke5 Kg6 4. Ke6 f4 5. h7 Kxh7 6. Kf7 f3 7. g6+ Kh6 8. g7 f2 9. g8=Q f1=Q+ 10. Ke7
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-1

do you mean this position? 

2Q5/8/8/8/3n4/8/1b6/k2K4 b - - 0 1
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  • 2
    No, BOTH sides must have only one move to draw.
    – Peter
    Mar 11, 2015 at 19:46

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