# Longest sequence with only moves to draw without a repetition

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.

• I truly wish (but doubt) that this is true of the starting position. 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

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 *
``````
• already pretty good! 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. May 29 at 15:44

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
``````

do you mean this position?

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